White Canker Tree Diagnostic Photos

My neighbor has a 25' tall ash tree. Last year there were a few dead interior branches and the bark didn't look too good. But the leaves weren't in bad shape. This May the leaves look great, but there are significantly more dead branches, and the bark looks worse.

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I snipped off one totally dead branch at the 6' level. This dead quarter-inch branch was about 6' up. This piece was about 1' from the branch tip. Most of it was clean, but some areas, such as this leaf scar, had large spore counts. The spores overwhelmingly cluster on parts of the branch having a large amount of scar tissue. Typically, this is where one year's growth ends and another begins, with very few spores on the bark in-between.

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This is a picture of the same branch, except that it is 10" from the branch tip. It shows a high spore density at the branch junctions. Other parts of the branch had practically no spores.

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This branch is still alive and has healthy-looking leaves. It was taken from the same area of the tree and is also about a quarter-inch thick. Except for a very tiny patch of spores at the branch junction, no other spores are present on this branch. However, note the leaf scar at the top of the picture. Where we might expect to see spores, we instead see small brown dots of about the same size. Could these be spore incubation sites?

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While there are no spores on this living branch yet, here we see another typical branch junction characteristic - many have lichen growing where we would expect spores. The lichen doesn't grow on any other parts of the branch.

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This area is a few more inches toward the tip of the branch. The bark here is sickly yellow and split. Even the inner bark is split (exposing the green cortex layer) and a black substance is growing underneath the bark. So this branch, while appearing healthy at first glance, is actually dying.

While the earlier pictures were taken in late May, the following set of pictures were taken in late September. At this time the white canker had already reproduced by shedding it's spores. Hence, spores were hard to find.

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White canker is on the sapwood (white), blocking the vessels, and is also within the inner bark, leaving a void. (400x)

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White canker growth has overrun the sapwood (plugging its vessels) and inner bark. It has also destroyed part of the outer bark, leaving a void. (400x)

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Here is a severe white canker infection - almost all the tissue under the outer bark is white canker tissue.(400x)

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The bright area is white canker growth. Notice that it is growing into the vessels and into the nearby void. The void, in turn, was probably opened up by the growing of the canker in the outer bark. (400x)

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This is a relatively large chunk of white canker just under the outer bark. (400x)

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White canker spores appear within the leaf, and white canker material appears to be growing out of the top of the leaf. (400x)

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The hypha on the leaf bottom is attached to a white canker spore. Seeing these spores is unusual this time of year. (400x)

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The bottom of this leaf has a fair amount of white canker material, and a hypha is caught here running completely through the leaf. (400x)

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This part of the leaf has canker on the top, bottom, and within the leaf! (400x)

Like the vast majority of white birches in this area, this one of mine was dying two years ago - its leaves were turning yellow and dropping off. However, the tree miraculously recovered after a fungicide spraying. While the first half of all the branches died, the outer half was saved and now appears very healthy. The following pictures were taken in late May, about a week before a major spore release.

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The branch junction shown here is about a foot from the end of a healthy branch. Its bark appears healthy and very few spores are present at the junction.

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This leaf stalk is about a foot closer to the trunk, and still on new growth. There are very few spores present.

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In contrast, here we see a section of the branch about 4' from the branch tip. There were a few dead twigs coming off this branch a few inches further toward this branch's tip. After that, all the twigs were alive. So this wood was probably created just before the fungicide spraying about two years ago - hence the high spore density at the branch junction.

With all those spores present, one would think that this tree should have a severe infection of white canker. Of course, to confirm a white canker infection, one needs more than tan dots. The following pictures were taken in early October using a 400x digital microscope. At this time the leaves were beginning to turn color and fall from the trees. The first two pictures below were from the bark of a twig about 3/16 inch in diameter. The third picture was of a leaf bottom.

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The bark shows few typical white canker objects. However, there are these numerous erupting white oval objects covered in what looks like crystalized snow.

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The bark is scattered with these oval erruptions. Each consists of particles of white canker on top, with tan wound wood showing through underneath.

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Generally a very boring leaf bottom! The only thing of note is the light sprinkling of these amber circles.

Sometimes the top surface of a leaf can display white canker disease symptoms. The following three photos show the the leaf top, although there's not much to see!

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The leaf top is sprinkled with these brown to amber spots. These spots seem to prefer leaf veins, and usually have canker material growing around them, as shown here.

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As usual, this amber spot sits directly on a leaf vein. But while veins are normally green, this particular vein seems to have been taken over by white canker.

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The association between the amber spots on the leaf top and white canker is particularly strong here. The combination resembles a fried egg - sunnyside up.

If you can't see anything of interest on the surfaces of the leaf, a look inside the leaf often proves more helpful. The following three pictures show cross-sections of the leaf, made by slicing a leaf with a razor and then examining the edge with a digital microscope at 400x.

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It now becomes more evident that the amber leaf spots seen so frequently on the top and bottom surface of the leaf are strongly associated with white canker. Here the amber spot has canker on the left, right, and especially the bottom/leaf interior. There is also a transparent tube of canker on the left, running from the top to the bottom of the leaf.

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Here is another one of those amber spots on the leaf top (red arrow). It is raised above the surface, and seems to have an extensive canker root system. The razor making this cross-section went from right to left. Therefore, the gap to the right of the canker once again seems to indicate that the canker material is relatively firm - at least more cohesive than the surrounding leaf tissue.

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This (red arrow) appears to be an amber spot on the bottom surface that was was torn downward by the razor making the leaf cross-section. It looks like the amber spot was closely allied with the canker which enveloped the leaf cells on the bottom surface and killed them, turning them transparent (you could say they were turned into a ghost!). It also looks like the amber spot is surrounded by bubble-wrap! Note that the leaf bottom is free of this blubble-like material where it was torn off but adjacent areas still have it. Also, check out the amber spot on the left (blue arrow) - it is more like a raised dome rather than the surface of sphere.

It's puzzling as to why white canker would go through the trouble to create these amber spots on the leaves when the leaves are only days away from dying and dropping off the tree. An alternative explanation is that the leaf creates these spots in response to a strong infection, in an attempt to wall off the infection, much as wound wood is used to close up a breach of the bark. Maybe that's why these spots are the color of wound wood.

The final set of pictures shows cross-sections of a 3/16 inch twig. Even though this is a very small part of the tree, if white canker is present, it shows up well in twigs. A nice side benefit is that twigs of this size are very easy to obtain using just a pruning clippers. Once again, all pictures were taken with a digital microscope at 400x.

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This is a photomerge of 5 pictures to show internal fracturing. The canker growing in the phloem is causing it to expand, causing an air gap to form between the xylem and phloem, which is being bridged by a few rays. The side benefit for the tree is that the canker is having a more difficult time jumping to and infecting the xylem.

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This is the most "normal" view of the entire twig cross-section. Still, blobs of white canker can be seen growing in the phloem, and the bark is beginning to separate at the far left and far right. In addition, white canker can be seen growing on the outside of the bark.

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There is extensive white canker present in the phloem in this view. White canker sits on the bark surface, and the destruction of the dark green cortex has left a void under the bark.

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A good example of the destruction of the outer phloem (just under the dark-green cortex layer, which in turn sits under the bark) by white canker. But the especially interesting feature is a spore of white canker sitting on the outside of the bark (red arrow). Note that directly under this spore the outer bark (blue arrow) has been completely replaced with canker material. And, the white spore substance above and below it are both sitting above their own resevoir (green arrows) of gray canker material under the bark.

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A good example of a battle between the bark of a tree and the white canker trying to destroy it. The bark is trying to grow wound wood around the canker in an attempt to heal the infection. But it looks like the canker is fighting back, creating extensive canker material on both sides of the wound wood.

In summary, at this time of the year it was very difficult to diagnose white canker with the unaided eye. Using a 400x microscope, the bark was only a little helpful in diagnosis. Views of the upper and lower part of infected leaves likewise weren't too helpful. However, leaf cross-sections showed that a good amount of white canker was present. But the best evidence of all once again came from a twig cross-section, where there was clear evidence of widespread white canker growth under the bark, specifically at the junction between the cortex and phloem.

A 10' high river birch tree planted several years ago has shown disease symptoms. The leaves look a bit ragged, and about 20% of its leaves turned yellow and were shed a few weeks ago. A year or two ago it had even more severe problems and almost died. A fungicide spray helped revive it. The following set of leaf pictures were taken in early August, using a 400 power digital microscope.

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While the leaftop was mostly clear, there were numerous elongated white objects that appeared to be erupting from the surface, as shown above. It appears as if these objects are forcing their way out, splitting the leaf surface in the process.

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The leaf tops were peppered with what looked like yellow egg yolks. Usually they were clustered near a leaf vein and very often they had a waxy white substance around them, as shown above, giving them the appearance of a fried egg.

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The leaf bottom was similar in that these egg yolk objects were far more common, as shown above.

The next set of pictures shows microscopic views of the bottom of the leaf. They are only a little more useful than the top set of pictures.

But even more information was contained within a cross-section of a 1/8 inch twig from the tree. These three pictures show that the green growth (cortex) and nourishment area (phloem) directly under the bark is riddled with white waxy growths (black arrows).

Note the blue 50μm scale bars in all the pictures. The purple arrow points to the white plastic vise grip used to hold the sample.

It seems likely that these white, waxy, cankerous growth areas are the probable cause of this tree's problems.

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Some parts of the leaf bottom also had lots of associated hair-like structures, as the above picture shows.

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The leaf vein accentuated this pattern, having far more "hair" on it, as well as a concentration of light orange globules. Several of the white spores seen on other plants were also present.

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The leaf stem was even more colorful, containing the same light-orange globules, light-yellow globules, white waxy objects, and translucent hairs.

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Our city park has a very large eastern red cedar tree whose leaves were looking a bit on the brown side. I also noticed other eastern red cedar trees in a similar condition, so I took a sample branch from the park tree for analysis. The branch is shown below, scanned at 300dpi, and sampled in late October.

Note: Commonly called Red Cedar, this tree is really a juniper, not a true cedar.

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Note that the leaves on the left-most twig seem a bit browner, or a less healthy green. On some trees, these twigs would turn totally brown and very easily break off.

One of the simplest analysis tasks is a microscopic look at the surface of a leaf. The following picture shows a leaf surface. Only one picture is shown, because, while many were taken, they all showed little evidence of any disease.

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The surface of all the leaves was generally the same as shown here - seemingly disease free. Here, however, a small exception is shown - a single white canker spore.

Photos of the cross-section of a leaf are more difficult to obtain, but potentially show more. That's the case here, as these 400x photos of a tiny leaf show.

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Note that there is lots of white canker present, but it's all buried within the leaf! That's why it's presence is not noticed when looking at the surface of the leaf. Hyphae are also present.

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This is the middle of the leaf - again some canker, but it's buried deeply within the leaf. The bright central spot is not white canker, but the leaf's main vein.

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Once again, there is substantial white canker present, but it's all deep within the leaf. There is also a blob at the right edge.

The examination of twig cross-sections usually gives better evidence of white canker than leaf cross-sections. The following twig cross-sections were made with a 400x microscope. The twig was about 3/16 inch in diameter - a convenient size for analysis.

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The outer edge of the phloem is almost all white canker (red arrow). The cortex (blue arrow)seems pink for some reason. But especially note the large amount of tan canker in the outer bark (yellow arrow).

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While the outer phloem here has quite a bit of white canker material present, it is more diffuse, as in other conifers, rather than globular. With the unaided eye, the twig cross-section looked like it had light brown areas where it should have been white with a shade of green, indicating infection was present. As this picture shows, the brown discoloration is strongest near the canker. Also, the normally green cortex is red here. This may or may not be normal. But note the more contained nature of the white canker in the outer bark.

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A few things to note here: 1) The most heavily infected phloem area appears to be surrounded by brown, diseased tissue. 2) There is no red cortex tissue here. 3) It looks like an old fragment of bark has old white spores under it (yellow arrows).

Examination of the bark of a twig can either be helpful or a waste of time. Often, the crucial factor is knowing exactly where on the bark to look. In the photos below, a random location was selected along with an area that past experience has show to be reliable as hosting numerous white canker spores.

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Much of the twig surface had a rough glassy look. But spore patches were also sometimes present (red arrow), as shown in this patch of bark.

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Another patch of spores. It appears as if these spores had landed and then sent out hyphae to infect the tree through its bark.

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This large patch of spores was located about a foot from the branch end, at a branch junction, which is the usual area for large bodies of spores to be found. These spores appear to be old.

In summary, while this eastern red cedar tree has a strong white canker infection, it is very difficult to determine this by a visual examination of the tree. Even though the canker is present within the leaves, it cannot be seen visually or with a microscopic surface inspection since it is buried deeply within the leaf. As in other infected conifers, leaf and twig cross-sections show diffuse patches of white canker infection. Twig cross-sections show white canker growths within the outer phloem, the cortex, and within the outer bark. It's the phloem disrupution that chokes off nutrients to the tree.

But really strong evidence of white canker infection comes from a 400x microscopic inspection of key areas of the branch's bark. Here we see many areas having a high population of white canker spores.

After seeing so many diseased leaves, I decided to check out an apparently disease-free Kwanzan Cherry. It was about 12' high and appeared to be about 10 years old. There were no apparent bark or leaf problems. The pictures below were taken in early August, using a 400x microscope. The blue lines are 50 micrometer scale bars. This is about the diameter of a white canker spore.

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This leaf top, near the vicinity of a stem, is virtually blemish-free. There is only the slightest evidence of a spore. The remainder of the leaf had no evidence of any disease.

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Leaf stems can be badly infected, but, as this picture shows, this leaf stem is in excellent shape, with no signs of disease.

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Even the leaf bottom shown here is problem-free.

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The first hint of a problem came when I ripped a leaf off of a branch and examined the leaf scar. Here you can see what appear to be very young spores just inside the leaf's green cortex layer. While very hard to see, they appear to have that characteristic cleft in them.

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While the bark of a twig infected with white canker will often be in poor shape with lots of spores, this twig's bark was unusually clean. I had to look hard to find the single infectious ribbon shown here (note that it appears to be emerging from a hole in the bark). Strangely, the color of the ribbon is pink. This ribbon went on for quite a bit and then entered the wood again.

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This might be a spore emerging from the wood (red arrow). Note that it seems to emerge at a bark split.

While the twig and bark pictures seem to show no white canker infection, the final "say" is usually determined by twig cross-section views, as shown in the following 400x microscope views taken of the cross-section of a 3/16 inch diameter twig. The bark is on the lower-left of each picture.

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The green cortex has no voids nor growths inside it, and has no gaps between it and the outer bark. However, the phloem tissue to the right contains some gaps which seem to host white hyphae. A red arrow shows the end of one such hypha, which is growing within a void it probably has eaten out as it was growing along the branch.

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This view more clearly shows evidence of a white canker infection. The green cortex is thin, contains white canker growths, and has separated from the bark. Furthermore, the adjacent phloem has several large clumps of white canker hyphae (red arrows).

In summary, this apparently healthy tree shows virtually no evidence of white canker when examining the leaf or twig surfaces. That correlates with the general appearance of the tree. Twig cross-sections, however, seem to tell a different story, since they expose the phloem and cortex - the focus of white canker. Here we see the very beginnings of a white canker infection. Consequently, we can expect this small tree to begin a steady decline in a year or two as the white canker slowly chokes off its nutrient supply.

While doing some heavy pruning of a Chokecherry tree, I uncovered more symptoms of white canker. This tree had become infected several years ago. One common symptom of white canker is fissures in the bark.

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This branch cross-section is about 2 inches thick and is about 7 years old. The saw blade cut very close to (but not through) one of these fissures. Note specifically that the fissure continues under the bark! The diseased wood at the center is dark in color, and shows that the disease came up through the core of the wood and spread outward. The disease expanded to the bark in the upper part of the picture, where it killed the inner bark. The holes in the wood, centered in the diseased area, were created where the saw blade pulled out wood weakened by disease.

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Here is a close-up of the area where the diseased area reached the bark.

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This is a high-resolution scanner picture looking directly at the bark fissure. Apparently the tree sensed that its inner bark was being killed and then initiated the growth of wound wood. However, unlike a physical injury, the outer bark was still intact. The pressure of the new wound wood growth then ruptured the bark, giving it the appearance of an explosion.

Look carefully at the bark around the fissure in the picture (click it to zoom in). You can just barely see that the bark surface is covered with a huge number of light yellow or tan spores. This tree disease is primed to spread itself via wind and rain to many other shrubs and trees!

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This is a sanded cross-section of another infected branch. The advancing black infection fronts are easily seen. Note that where these infection fronts hit the inner bark, that bark appears thicker. It really isn’t. Instead, the green and life sustaining phloem has been killed there (you can see it if you look carefully). This branch is about 40% dead based upon the size of the phloem thickness. Eventually, all the phloem will die and then the leaves will dry up and also die. As the leaves starve, opportunistic infections may move in.

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This is a microscopic view of the area shown in picture 4. If you look carefully, you can see the semi-transparent hyphae, and the damage they have done to the wood.

While the earlier pictures were taken in late May, the following set of twig and leaf pictures were taken in late September. At this time the white canker had already reproduced by shedding it's spores. Hence, spores were hard to find.

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Extensive white canker growth under and within the outer bark. (400x)

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Here there is extensive canker growth in the outer sapwood, under the bark. (400x)

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A large chunk of frothy white canker (red arrow). The frothy texture was probably caused by a razor cut through it. A hypha grows to the lower-left of it. Note that the green sapwood is splitting due to canker growth (blue arrow). (400x)

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A good example of a cut through a layer of ice-like white canker growing on the surface of the bark. There are also spores under the bark. (400x)

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A section of bark and sapwood under severe attack by white canker. (400x)

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This area was under such severe attack from canker particles that it caused a huge void between the sapwood and the bark. (400x)

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It appears that white canker engulfed the surface leaf cells and absorbed them. Possibly, as these leaf cells die, they turn brown, and then become transparent? (400x)

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This the upper leaf surface. It's a good view of how the white canker within the leaf is spreading out within the leaf interior. (400x)

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While examining the leaf surface, I found this hypha with an attached young spore. These two objects usually aren't so openly visible. (400x)

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This leaf didn't look too bad visually, but some parts seemed to contain a lot of canker, as shown here. (400x)

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This part of the leaf seemed to have a lot of canker near both surfaces. (400x)

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Some parts of the leaf, such as here, were really mangled with white canker. (400x)

Our yard contains a small "Stellar Pink" dogwood tree. This is a Rutger’s hybrid variety, and as such is claimed to be resistant to the anthracnose disease that is killing native dogwoods. While it appeared healthy during it's first year, it began a steady decline in the following years.

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Pictures 1 and 2 are of the same branch, scanned at 2400 dpi. While picture 1 shows the tip of a branch, picture 2 shows the bark further on down toward the trunk. The terminal growth shown in picture 1 is distorted, indicating an infection. Picture 2 shows that the slightly older growth contains an abundance of yellow spores. Extensive lichen growth is also present near the spores.

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Pictures 1 and 2 are of the same branch, scanned at 2400 dpi. While picture 1 shows the tip of a branch, picture 2 shows the bark further on down toward the trunk. The terminal growth shown in picture 1 is distorted, indicating an infection. Picture 2 shows that the slightly older growth contains an abundance of yellow spores. Extensive lichen growth is also present near the spores.

Suspecting the leaves might show some disease evidence, I placed a diseased leaf from this tree in a vise and used a razor to slice off the protruding piece. A 400x digital microscope was then used to photograph several leaf cross-sections, as shown below.

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The start of the leaf slice exposed buried white canker material (red arrow).

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White canker material on the lower leaf surface.

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A patch of extensive white canker growth at and near the lower leaf surface.

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White canker material near a leaf vein. A white canker spore also seems to be present.

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Another patch of white canker growth accompanied with hyphae growing through the lower leaf surface.

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More white canker on the lower leaf surface, along with its hyphae. Note that one patch of hyphae is also growing out of the top of the leaf, and may also extend out of the bottom of the leaf.

In general, most of the white canker is buried within the leaf, and tends to be milk-white in color. This color fades to a translucent light white (or gray) for canker material on or near the surface.

As informative as these leaf cross-sections are, twig cross-sections are often even more useful, as shown by the following 400x microscope pictures.

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The phloem here has a relatively large area of embedded white canker growing up through it. Notice that where the white canker density is highest, the bark next to it has lifted and turned a "peanut butter brown" color.

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The growth of the white canker under the bark has split the phloem layer, creating voids (red arrows), and cutting off the bark from nourishment. The bark here is bulging out, and white canker material is growing on that bulge. The dark brown bark will mix with the white of the white canker, giving an external visual appearance of light brown.

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Here again, the white canker growing under the bark is creating a void by splitting the phloem layer and causing the bark to bulge out. Notice that the canker material near the void is tending to form a spore-like object. Also notice the large blobs of white canker material growing on the surface of the bark.

In summary, the distorted new growth and the large number of tan spots on a new branch give strong hints of white canker. The leaf cross-sections reinforce this diagnosis. The strongest evidence comes from a twig cross-section, where the white canker can be seen growing in the nutrient-rich phloem, splitting the phloem, pushing the bark out, and causing white canker to grow on the bark's surface. Finally, internal white canker tends to be milk-white in color and opaque, while external white canker tends to be a translucent light-gray.

This is one of those relatively new "Dutch Elm disease-resistant" trees. It's a fairly young tree, only about 8' tall and was planted in an attempt to bring back the beautiful elms, which at one time were so abundant on our city streets.

About 20% of the leaves were suffering from insect damage, having holes eaten out of them. I wondered if that was because the tree was somewhat weakened. Except for this insect damage, the leaves didn't look bad at all. This data was gathered in early June, 2008.

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As you can see, this quarter-inch branch has relatively few spores present (the light-yellow dots), and they don't seem to be clustered at the branch junction.

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There seems to be a thin, transparent substance on the surface of the bark here. A single spore is also present.

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There are many young spores present here, and they seem to have created a tangled web of hyphae around them.

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More spores are present here. They all have basically the same shape and color. Quite a bit of translucent cankerous material is also present.

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Tangled leaf hyphae on the bottom of a leaf at 400x. It's said that the hyphae do the real damage to a plant. The bottom of this leaf contained a large number of these hyphae. On the other hand, these hyphae didn't resemble normal white canker hyphae.

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These pictures show more hyphae on the leaf bottom, along with some strange large dark globular objects. These objects are clearly connected to the hyphae, and could be what are called "resting structures", technically known as chlamydospores. These object's strong resemblance to chlamydospores increases the probability that white canker is a fungal disease. On the other hand, the hyphae associated with these objects doesn't look like typical white canker hyphae.

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These pictures show even more hyphae, but here they are associated with the bottom leaf vein. Some of the branching is clearly spider-like, which is termed a mycelium. However, once again, the shape of this hyphae (round) is not characteristic of white canker (ribbon-like), even though both are translucent in appearance.

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As this picture shows, the top of the leaf had only a few hyphae. One spore and hypha is shown here. You can just barely make out the hypha it has generated. The bottom of the leaf had almost no spores.

Since the evidence for a white canker infection didn't seem conclusive, I returned to examine this tree in early November. While no leaves were present, the bark seemed to be splitting in some areas, particularly around the branche junctions. I clipped off one branch for examination under a microscope. The results are shown below.

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The green cortex under the outer bark is barely present. The phloem under it is an unhealthy brown. Particles of white canker are present, as is a hypha.

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The green cortex under the outer bark is virtually gone. The phloem under it is an unhealthy brown. Particles of white canker are present at the cortex-phloem junction, soaking up any remaining nutrients. These particles have the size, shape, and color of white canker spores.

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The green cortex under the outer bark is totally gone. The phloem under it is an unhealthy brown, has a rough texture, and has hyphae embedded within it.

The above cross-section views of a 3/4 inch twig provide strong evidence of white canker. The bark of the twig was examined next. Few spores were found between branch nodes. In contrast, there was a large sprinkling of white canker spores at the branch nodes, as shown in the pictures below.

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In conclusion, it appears that this elm has been newly infected with white canker. However, the numerous hyphae and dark globular objects seem to hint that some other infection is also taking place. Nevertheless, the late fall twig cross-sections show that a white canker infection is taking place. The abundance of white canker spores at the branch junctions (nodes) provides the most convincing evidence of white canker. I expect to see a serious decline in the health of this young tree next summer.

This 12' tall Siberian elm belongs to my neighbor. It's not in bad shape, but there is clearly something wrong with it, since some of the leaves have spots and the tree seems to be thinning somewhat. The branch was cut in early June.

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This is a portion of a branch cut from the tree. It has a diameter of about 1/2 inch and was taken from a larger branch about 6' high. Close examination shows only a minimal number of spores at the branch junctions. Yet that is the exact location favored by white canker spores.

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A microscope view of a branch cross section shows several transparent spores just inside the bark (black arrows).

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There is a lot to see in this 400x microscope picture! The bark is in the lower-left corner (A). The green cortex lies under it(B). Under that is the phloem, which should be uniform in appearance. Instead, it contains numerous gelatinous blobs(C). The phloem, in turn, should meet the white xylem cleanly. It does that at one area (D). But note the blob of white canker material growing between the phloem and xylem (E)! This canker is separating the xylem from the phloem (F). This cankerous blob is connected to a hypha that runs down a conducting vessel of the xylem(G).

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This picture shows a large amorphous white structure that doesn't appear at all like wood. While it may be white canker, it could also be a dislodged piece of xylem.

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This growth is just under the bark. The phloem appears to have been replaced with a pinkish canker material that has blobs of white canker growing through it.

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This is what the pith at the center of the branch looks like - a white frothy substance. It should be surrounded by wood (xylem) resembling normal tree rings. But note the areas of white cankerous material just outside the pith (black arrows).

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The brown substance running from the lower-left to the upper-right is the bark. Note that there is no underlying cortex - the bark has separated from it! The milk-white substance appears to be white canker. The semi-transparent hyphae are also a form of white canker.

Unlike other trees, this Siberian elm is not a host to extensive spore patches on its bark or leaves. Instead, the evidence of white canker infection can be seen when viewing twig cross-sections with a microscope. As in other trees, the nutrient transporting phloem layer is attacked and consumed. But unlike other trees, there is also evidence that xylem tissue is also attacked.

On a recent (July 2008) trip to the south shore of Lake Superior (Upper Michigan peninsula), I noticed that a lot of the fir trees there were dead. They were a bright orange-brown in color. I searched for one that was about 5' tall and that was only half-dead, and snipped a half-dead branch from it. Upon returning home, I examined a cross-section of a 3/16" branch and examined it with a 400 power microscope. The results are shown below.

1

This picture shows normal, healthy tissue - evenly layered with a clean junction between the xylem and phloem.

2

In contrast, the remainder of the bark around the twig was in far worse shape. In this view, the xylem-phloem junction is still clean, but further out there appears to be some hyphae infesting the bark.

3

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The segment of the cross-section shown above is so disturbed that it no longer even looks like bark. Note the white spore near the large waxy blob (blue arrow). Note the blue 50μm scale bar below the spore.

4

This picture shows strong evidence of white canker infection. There is so much white canker growth at the phloem-cortex interface that the bark is bulging out. And right in the center of this bulge are two buried white canker spores (just above the blue 50μm scale bar). Follow this bulge inward, toward the twig center, and you can see the underlying phloem and xylem are tinged milk-white, a sign that they too are infested with white canker. Surprisingly, this hasn't affected their structure.

5

The white canker infection damage shown here is even larger than that shown in picture 5. The normally green cortex has turned blood-red. Underneath it, various shaped blobs of white canker are digesting and destroying the phloem, leaving voids in the process.

The twig cross-section views shown above reflect the tree's health very well. Some cross-section pictures show healthy tissue, while others show severe infection. Pictures 4 and 5 are especially convincing evidence that this tree is dying due a white canker infection.

Ginkgo trees go back about 150 million years, so they've probably survived more diseases than any other tree. This particular tree is relatively small - about 10' tall. It was planted only a year or two ago. Yet, it is showing signs of stress. Many of its leaves look stunted while some are almost full size. But virtually no other leaf damage is apparent. The branches are also surprisingly clean, and host almost no spores. This tree was sampled in early June.

1

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I cut off most of the leaves at this leaf node in order to be able to scan this branch, and also to highlight the diseased leaves. The leaf on the left appears shriveled, as if badly diseased. Two other leaves were so diseased that they didn't develop at all (black arrows). The base of the leaves at this node contain a lot of "hair". This hair is associated with some tree diseases.

2

This is a particularly good shot of the "hair" at the leaf junction area. Two new leaves that died during development are also shown.

3

4

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A 400x microscope view of this "hair" shows that it is really a tangled mass of hyphae. More important, this hyphae contains both an immature spore (red arrow) and two mature spores of white canker (black arrows).

5

6

This 400x set of pictures, taken at a hyphae cluster near the leaf surface, shows numerous white canker spores. These pictures were taken in early June, within a day or two of a major white canker spore release. Note that these spores have a yellow tinge to them, which is characteristic of very new spores. Some are so new, that if you look very closely, you can even see a touch of yellow embryonic tissue between the spore lobes (click the picture to zoom in).

Unlike other trees, the Ginkgo seems to be trying to prevent white canker spores from emerging through its bark and propagating. In turn, white canker spores have found that they can grow out of the leaf junction area, where there is no bark. As a last line of defense, the Ginkgo seems to be throwing up a tangle of hyphae to trap the emerging spores so that they have trouble propagating. The destructive part of the white canker infection is lurking under the bark, within the tree tissue, slowly destroying it.

I have more than an average interest in Ginkgo trees, partly because their leaf shape is so distinctive and partly because they have been around so long its like looking at a living fossil. Although ginkgo trees are attractive (not the female trees, since their fruit is foul smelling), they are not widely planted. But I found a group of about 7 young trees in Evergreen cemetery up in Portland Maine. I've been following their health for several years, and noted a progressive decline, with the symptom being leaf spots. So early this October I clipped a twig whose leaves showed such spots and brought it home for analysis. The results are shown below.

1

Of all the diseased branches on this group of ginkgo trees, this branch seemed to be the most diseased. But they all shared the same leaf spot infection symptom. Interestingly, the vast majority of trees in this cemetery are maples, and maple trees seem very susceptible to getting and spreading white canker.

2

A sample leaf showing lots of disease symptoms. Spores can be seen in the dead areas. This is the leaf used in the leaf surface and cross-section views below. (The circular arc impressions were from my examinations with a digital microscope.) (1200 dpi)

The next set of pictures shows the top of the leaf. The numerous dead and discolored areas hint at severe leaf damage, and the following microscopic pictures detail exactly what this damage is.

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3

Notice the dead white area and the white canker at the edge. One hypha is poking through a hole (red arrow). Most of the normal green leaf looked like the surface in the upper right corner. (400x)

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4

A clean area is surrounded by a branching white canker infection. There are two white spores (red arrows) adjacent to this "river of canker". (400x)

5

This picture reminds one of an explosion in a liquid, with the hyphae of white canker representing liquid streams splashing from the center finger-shaped dead leaf area. (400x)

The leaf bottom can also give some insight as to what is going on. The next two pictures show the leaf bottom. In particular, the contrast between the live and dead areas is of interest.

6

The edge of a dead area. The white blobs seem to be either particles of white canker or leaf cells that have been overrun with white canker. Notice that the white canker infects the leaf vein as well as the leaf cells. In fact, you can see the canker tentacles spreading out from each tubule in the leaf vein if you look closely. (400x)

7

An advancing front of dead leaf tissue. The ghostly white blobs in this dead area may be leaf breathing holes (stomata) that were infected and killed. (400x)

Somewhat surprisingly, leaf cross-sections seem to provide some of the most informative data regarding white canker infection. Specifically, it is the area between relatively healthy leaf tissue and diseased dead tissue that shows us detailed white canker information, as shown below.

8

An infected and torn leaf vein appears on the left. To its right are two canker particles on small stalks, and immediately to their right is a area being killed by white canker. Killed leaf material is shown to the right of that. (400x)

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9

Relatively healthy green leaf tissue on the right. Dead, shrunken leaf tissue on the far left. The battle line is in between, which is swollen with white canker material. Notice where the razor cut off a white canker white hypha (red arrow). (400x)

10

Another leaf infection boundary where the white canker growth is consuming the healthy leaf tissue. The leaf cells seem to turn transparent in the initial infection stage, then tan, and then black. (400x)

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11

A good title for this picture might be "white canker gone wild", since it seems to have completely destroyed this part of the leaf with various forms of canker material. Note also the hypha snaking through the dead leaf tissue (red arrow). (400x)

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12

Another white canker infection front. A big hypha can be seen on the edge of the green tissue on the left (red arrow). Numerous smaller white canker growths can be seen on the right. The most vigorous white canker growth is seen where the green leaf tissue ends. After the white canker has killed the leaf tissue, it seems to start sending out transparent hyphae to find other tissue to infect. (400x)

The most consistantly reliable way of detecting white canker appears to be the microscopic examination of a twig cross-section. This can show the presence of white canker even if there is no evidence of it when looking at the bark or leaves. So while the preceeding pictures give strong confidence of the presence of white canker, the following twig cross-section pictures pile on even more evidence of its presence.

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13

Lots of canker here. In fact, you can see one plume of it rising up and through the bark and giving rise to a spore (which appears to be ruptured) (red arrows). Another plume is trying to break through the bark. And the brilliant white area indicates that there is lots of canker growth in the phloem, the energy-rich part of the wood. (400x)

14

There are huge billows of canker growth in the phloem. Also, a large body of canker is pushing its way up through the bark. The bark appears to be about 80% destroyed in this area. (400x)

15

The beige colored area on the far left is the xylem, and, like other trees, it is virtually unaffected by canker growth. But to the right is the phloem, and the brilliant white blobs show that white canker is rampant throughout it, so much so that the phloem is separating from itself and from the xylem. Except for the extreme outer surface, the outer bark has been almost totally infected with canker. (400x)

16

This is what lichen looks like. Notice that the appearance is different from canker. Lichen has a blue-green tinge to it, while white canker is white or light gray. (400x)

17

Lichen roots can be seen digging into the bark. The lichen surface also seems to have a lot more debris on it than a canker would. (400x)

18

A tip of blue-green lichen on a quarter-inch thick branch. (400x)

Recall from the first picture that there was some lichen on the branch. For comparison purposes, here are some pictures of that blue-green lichen using a digital microscope set to 400x magnification.

I spotted a large sick looking Honey Locust tree about a mile from my house. Its foliage was somewhat thinner than normal and many of the lower branches were dead. In early June I removed the tip of one of these dead branches. It was about a quarter inch thick and is shown in the first picture below.

1

The tan discoloraton almost appears as if it were spray painted on. In fact, this discoloration is due to a large number of tiny spores. They were found almost exclusively on one side of the branch.

2

3

The above two pictures are 400x digital microscope views of the tan area at the branch junction shown in picture 1. The white objects look exactly like the white canker spores seen on other trees and shrubs.

In early October, hoping to gather more conclusive evidence of white canker infection, I returned to this tree to obtain a branch that I could examine with a digital microscope. The following set of pictures confirm the white canker infection. The first three pictures are of leaf tops.

4

There wasn't much evidence of infection on the leaf's top, as shown here. Only occasional white areas like this gave a hint of the canker within.

5

These two areas show a bit more evidence of white canker infection. The canker on the left is probably below the surface, but the one on the right is on the surface - you can just make out the stalk where it connects to a leaf vein. The brown stick-like object is probably another infection.

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6

This isn't a leaf top, but the torn end of the leaf stem. The crystal clear tissue on the right (red arrows) probably indicates that white canker destroyed all the chlorophyll.

Usually leaf bottoms are an even better indicator of white canker infections that leaf tops. That's not quite true here, as shown in these microscope leaf bottom pictures.

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7

Surprisingly, the leaf bottom was fairly clean. Only near the stem were there any hints of infection. Here there is a blob of canker material on the stem. There is also what appears to be a dead white canker spore (red arrow).

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8

The leaf stem with lots of hyphae growing from it. But note the yellow sphere. It appears to be connected to the stem with a barely discernable hypha (red arrow), so it probably isn't an insect egg. In addition, if you look closely, the stem hypha in the upper left (blue arrow) appears to be developing a yellow swelling at its base.

9

As we get close to stem at the base of the leaf, the number of hyphae proliferate like grass. But the white blobs under the leaf surface make one wonder if the blobs aren't canker responsible for this hyphae growth.

↑ ↑ ←

10

There are a lot of hyphae on a leaf vein, particularly near the base. So here I did a cross-section of a leaf base where there were lots of hyphae. This shows there is a difference between a normal leaf hair (red arrow) and a white canker hyphae (blue arrow). Both are semi-transparent. Leaf hair has a round cross-section, a smooth surface, and gradually tapers to a point. Canker hypha, in contrast, is more like a ribbon. It has a 1:4 cross-section aspect ratio, twists, is lumpy, and tends to run for a relatively long distance. They also tend to have an occasional black spot and occasional tiny protrusions (yellow arrow - small root-like structures).

Leaf cross-section views with a microscope will often give a good indication as to whether white canker exists, and how pervasive it is. However, in the case of honey locust trees, these views aren't that useful, as the following three pictures show.

11

The leaf cross-sections actually show little of interest. Here is an exception where canker extends both below and above the leaf surface.

12

In the middle of this leaf cross-section, you can see a blob of canker. However, its shape appears as if it might be a leaf vein that was consumed by white canker.

13

Here the leaf's cross-section is hidden. White canker will sometimes cover the leaf's surface and infect and kill the surface cells. Then, when a razor tries to slice through this tougher material, it instead lifts it up as a sheet and drops it elsewhere, as was done here. This action seems similar to a bad sunburn, where the surface skin cells die and then later peel off in small sheets.

The most reliable white canker diagnostic views are twig cross-section views. They have an added advantage in that they don't degrade over the course of a few days or weeks, as leaves do. This reliable disgnostic evidence is confirmed by the 6 twig cross-section pictures below, taken with a 400x digital microscope.

14

Extensive canker damage. The phloem has a void in the middle of it and the dark green cortex is virtually gone. Even the outer xylem has a large void! Most telling of all, the top bark has such a significant canker growth that it is bursting out of the bark and looks like a volcano.

15

Reasonably healthy area area with intact outer bark. But there is beginning to be a large amount of canker growth between the dark green cortex and the phloem - lots of tan canker particles are building up there.

Pith Xylem

16

This is the junction of the pith (twig center) and the xylem (area with all the vessels). I usually ignore this area since there's not much of interest there, but in this case the canker has grown here too.

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17

There is an extensive area of snow-white canker tubule growth here just under the bark. But notice also the several areas where the canker is growing on the bark - it is eating away the bark, blackening and destroying the surrounding area as it does so (blue arrows).

18

White canker appears to be tougher than regular wood, so when a cut is made through the wood, it will sometimes dislodge a solid chunk of this canker. Apparently that is what happened here, giving us a good view of pure white canker.

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19

Lots of information in this view. On the far right is a major battle between the white canker and the tree's bark, causing an eruption through the bark, with clear white canker bubbling out the top (red arrow). In the middle of this picture is an infected area of white canker, indicated by the white particles (blue arrow). Interestingly, underneath it we can see that it has also infected the rays, which look like white nails (green arrow). And above it, the canker appears to be pushing the bark out a bit. White canker has even broken through on the outer bark, as seen by the out-of-focus white particles on the bark's surface (yellow arrow).

Several years ago, when this disease was at it's worst and affecting all of my trees and shrubs, this tree appeared to be the least affected. So, when I first started to scan a branch of this tree, I assumed I wouldn't find many spores. I was wrong - there was an abundance of spores, leading me to conclude that while it too was heavily infected, it didn't show its infection as readily through distorted leaf growth as did other trees and shrubs.

One of the attractions of a Japanese Stewartia is its unusual characteristic of having naturally exfoliating (peeling) bark. However, a major characteristic of white canker is split and peeling bark. Therefore, it's particularly hard to diagnose this disease on a Japanese Stewartia by its lack of intact bark or distorted leaves. The tree may look healthy, but be badly diseased, as the following pictures show.

This particular Japanese Stewartia tree is about 10' high.

1

This branch section was about 8" from the branch tip, and about 4' off the ground. It has a relatively small spore density - all spores are concentrated at the branch junction. There are also dark brown spots in close proximity to the spores.

2

This branch segment, about 2' in from the branch tip, also shows an abundance of spores at the branch junction. Nearby junctions also have a high spore density.

3

While not as numerous, the bark between junctions also has a significant spore density, as this picture shows. Strangely, when I flipped this branch over to scan the top side, I saw virtually no spores at all! But I did see a few bark splits and dark spots. The dark brown spots were mainly at the branch junction, hinting that they are associated with infected areas.

4

This is a cross-section of the 1/4" branch shown in picture 3. Visually, it appears healthy. That's because the damage is mainly microscopic, as the next pictures show.

The above pictures were taken in early May, 2008, using a scanner. The following pictures were taken two months later, in early August, using a 400 power microscope. The short blue lines in all the pictures are 50μm scale bars. This is the approximate diameter of a white canker spore.

5

This is an area around the stem on the bottom of the leaf. The vein hairs are normal. There is only a single spore showing - its above the 50μ blue leaf scale bar. The remainder of the leaf bottom is free of any sign of disease.

6

These two leaftop pictures show almost a complete absence of any disease symptoms. The faint white spots in picture 6 are likely white canker blobs within the leaf interior. There appears to be a buried hypha and spore in picture 7 (black arrow). The brown spherical object in picture 7 is unknown.

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7

8

Looking over the bark of a twig microscopically, there was again little evidence of infection. While this is at odds with pictures 1, 2, and 3, those pictures were taken in late May, about a week before a major spore release. These microscope pictures were taken in early August, two months after the spore release. In spite of this, I did find one pocket of spores (shown here) located at the junction of a twig and its parent branch. This junction is where white canker spores usually are found. Note, however, that the spores are now milk white, and have lost their youthful yellow tinge.

9

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A microscopically examined twig cross-section turned out to be the best indicator of white canker. Here you can see that the normally green phloem is almost half-consumed with white canker material. There is also a layer of white canker material within the outer bark (blue arrow), and some on the surface of the outer bark (red arrow).

10

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In this cross-section segment, white canker has consumed almost all of the green phloem, about half the outer bark, and is starting to consume the xylem (sapwood). Note that the white canker substance is all a uniform gray in color, while the xylem is milk white. The black arrow shows where the canker found a void and grew into it.

11

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White canker growth is often diffuse. The exception is where it is forming a spore. It tends to form spores in an internal void (a pretty useless strategy), in the outer bark (also useless), or on the surface of the outer bark (far more productive). Here we see a spore growing within the outer bark (black arrow). There was so much canker growth in the phloem under it that the outer bark was pushed out.

In summary, a visual check of deformed leaves or separating bark will not be helpful in diagnosing white canker. Instead, examination with a microscope is needed. The best place to check for white canker spores is on the underside of branch junctions, a foot or two from the branch tip. Another good way to diagnose white canker is to examine a twig (e.g., 3/16" diameter) cross-section and check for patches of a gray-white substance within the phloem and within the bark. If there is a void between the phloem and the outer bark, or if the white canker has invaded the xylem, then the infection is particularly severe.

There is a nearby Linden tree which was in a bit of decline last year. This spring it was slow to leaf out. When it did, there were fewer leaves than last year.

1

One classic symptom of this disease is that all the leaves die on a branch except those at the tip of the branch. This picture shows such a branch taken from this linden tree.

2

Further away from the tip, as the twig coloration turns from green to a normal bark-brown, what looks like cobwebs start appearing first. Shortly thereafter, it looks like some clumps of brown dirt are mixed in with the cobwebs. A bit further on and spores begin to appear.

3

As on other trees and shrubs, the spores seem to appear more often near a branch junction or on a leaf stem. On the other hand, they often appear only on one side of the stem and tend to cluster there. This picture shows a cluster of spores on and near a leaf scar.

While the earlier pictures were taken in late May, the following set of pictures were taken in late September. At this time the white canker had already reproduced by shedding it's spores. Hence, spores were hard to find in the following branch and leaf cross-section microscopic views.

4

The inner bark is pretty much corrupted by white canker. (400x)

5

Large chunks of canker are errupting from the vessels. (400x)

6

Ice-white white canker hyphae are heavily colonizing the bark. (400x)

7

Parts of the inner conducting sapwood are also being blocked due to canker growth. (400x)

↓ →

8

Lots of canker and tissue corruption. Also, note the white hypha coming up through a vessel, exiting the bark, and generating a blob of white canker outside the bark (red arrows). (400x)

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9

Here, as in several other areas, the canker seems to follow rays leading to the branch center. Also, note that canker growth has separated the bark here (red arrows). (400x)

10

Here is good evidence here for distinguishing white canker from a leaf vein, which also tends to be white. The canker tends to run from the top to the bottom of a leaf. A vein is round, white, and frothy, and the leaf tends to bulge around it. (400x)

11

Two definite white canker blobs on the bottom of the leaf. (400x)

12

More instances of white canker extending from the bottom to the top of a leaf. (400x)

13

White canker runs from the top to the bottom of the leaf here, and some pieces of it are being shed from the top of the leaf. (400x)

There is a 12' Japanese Maple tree in our neighborhood. Several years ago I noticed the bark was beginning to split along some branches that were several inches thick. Yet the foliage looked fine, and most people would have said it was a beautiful, healthy tree. Last year the bark splitting was worse, and about 20% of the tree was dead. Strangely, it retained many of its dead leaves over the winter, something it had never done before. I figured that was not a good sign. Sure enough, this spring (2008) the tree is now about 80% dead.

1

There is a heavy concentration of spores on the scars at the branch junctions, as shown in this view. Strangely, spores are not present on the surrounding bark, as on other trees.

2

There were also spores at the leaf scars, as shown here. The remainder of the branches had very few spores on them.

While the earlier pictures were taken in late May, the following set of twig and leaf cross-section microscopic pictures were taken in late September. At this time the white canker had already reproduced by shedding it's spores. Hence, spores were hard to find.

3

Here is a section of sapwood riddled with canker particles. They are also present on the inner bark, and some can be seen on the outer bark. (400x)

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4

The inner bark has been greatly mangled by canker growth. In particular, note the blob of gray canker material near the bottom of this view (red arrow). It has that typical foamy look. (400x)

5

An unusually insightful view showing a number of growth rings, each infected with white canker. It shows this twig was infected with white canker about three years ago, which is about when the tree's decline started. Also notice the patches of white canker infection in the outer bark. (400x)

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6

The item of interest here is that gray-white blob at the end of the void under the bark (red arrow). Is it a canker eating the sapwood or an insect eating it? (400x)

7

In this leaf cross-section, we see a typical example of a white canker growth extending completely through the leaf, and the the canker on each side of the leaf is starting to bud off hypha. (400x)

8

The interesting part of this picture is that there is a large spore collection on the left which is bulging out of the leaf, and it seems to be connected within the leaf to the parallel set of white tubes emerging upward on the right. (400x)

9

A hypha runs through the leaf from the upper-left to a canker blob at the lower right. This blob is emitting a hypha from its tip. The hypha in turn has turned upward to touch the leaf surface, and has begun to infect it with what looks like a spore. (400x)

10

Great example of two white canker blobs, each connected to a hypha. The blob's granular appearance hints that it envelops the leaf cells, digesting them in order to get energy to send out hyphae, which in turn spreads the infection. (400x)

A neighbor of mine had a Norway Maple that looked sick, and asked me to take a look at it. In spite of the grass being lush and green, showing there was sufficient water and nutrients available, the leaves were drooping. This was at the end of May, when growth should have been vigorous. Pictures of some leaves taken from this tree are shown below.

1

In addition to the wrinkled and limp appearance of this leaf, there are also red blotches present.

2

A 2400 dpi close-up of one of these red areas shows that it is due to eriophyid mites, which don't cause serious tree injury.

3

Another leaf was also wrinkled. But it had finger-like protrusions instead.

4

This is a 2400dpi close-up of those protrusions (nipple gall?)

5

Picture 5 shows a close-up of a branch junction. Click on the picture to zoom in, and you will see numerous tan particles right at the junction area. Inset pictures 6 and 7 were obtained using a 400x digital microscope and shows that these particles are actually spores of white canker that are sapping the tree of energy. The weakened tree probably makes the tree susceptible to other attacks, such as mite infestations.

6

7

Having gained more experience in analysis, I returned to this tree in mid-October to again gather some branch and leaf samples. However, during the summer this tree had been sprayed with a fungicide to ward off disease. The following pictures were obtained using a 400x digital microscope.

8

This leaf top is unusually clean - there are just two small traces of canker here (two white streaks).

9

This top view is the edge of a leaf tear, due to mechanical damage or disease. It looks like canker has taken over the dead part.

10

While the leaf top is unusually clean, there is a hint that some canker lies just below the surface.

11

The leaf bottom is also unusually clean. Here is the edge of a tear. There is also a hypha to the right of it. The white material looks like, but may not be, white canker.

The following five pictures are all leaf cross-section views, obtained using a 400 power digital microscope.

12

There is a pillar of white canker running from to the of the leaf to the bottom. Two pieces of canker are also hanging off the bottom of the leaf.

13

A tangled hypha on the top of this leaf indicates the probable presence of white canker. A few pieces also hang off the bottom of the leaf.

14

This picture shows that much of the white canker that is present lies within the leaf rather than at or on the surface of it.

15

There is a high density of white canker just to the left of center, both on the leaf surfaces and within the leaf.

16

This is a leaf vein. The pith is in the center. But it appears as if the top of this vein has been infected with white canker.

The next three pictures are twig cross-section views, obtained using a 400x digital microscope.

17

It appears the fungicide spraying helped, as this area of the bark is relatively clean and healthy - the bark and phloem are intact, with only traces of white canker.

18

The phloem is distorted here, with white canker growing in its outer part and within the bark. It looks like some hyphae are also pushing through the bark. Note the slight bulge in the bark developing at this point.

19

Another area where white canker is developing in the outer phloem and the inner bark, pushing a piece of outer bark out.

In summary, while white canker is present in this tree, the summer fungicide spraying has reduced the infection significantly - to the point where only microscopic views provide useful diagnostic evidence. The bottoms and tops of the leaves give only a hint of infection. The leaf cross-sections more clearly show signs of infection. But once again, the clearest sign of white canker infection is seen in twig cross-sections, where the white canker is concentrated at the outer phloem and the inside of the bark. This is the area high in nutrients.

My next-door neighbor has a 25' tall Norway maple tree that had started to decline about 5 years ago. Three years ago, and again 2 years ago, it had been sprayed with a fungicide, and made a miraculous recovery, meaning that all leaf drop stopped and the leaves returned to a healthy rich deep green color. This year it had not been sprayed, but appeared reasonably healthy until several weeks ago (the start of August). Since then the leaves have been falling at a relatively high rate. Picture 1 shows a typical leaf. The leaves have a dry, wrinkled look, as if they lack water. Yet, the past several months have been exceptionally wet due to a persistent rainy weather system.

1

This leaf appears to have anthracnose, but other evidence hints that anthracnose is likely a secondary disease.

Suspecting that there may be an underlying cause to this tree's problems, I used a 400x digital microscope to examine other parts of the tree. Three leaf and twig pictures are shown below. The blue lines are 50 micrometer scale bars.

2

The leaf top surface is generally clean, with only a hint of white canker.

3

Likewise, the leaf bottom only shows hints of a white canker infection.

4

This twig shaving view shows hints of trouble: there are numerous spores on the bark's surface, and underneath the bark there is a white substance above the green cortex.

I used the same 400x microscope to examine some 3/16" twig cross-cut views next, with the results shown below.

5

This picture shows a healthy area - the white xylem joins the green phloem with no air gaps to be seen. Look closely, however, and there are signs of white canker just beginning to infect the phloem.

6

Far more common is the disorganized growth shown here, where the rich green of the phloem is being replaced with white canker material that ranges from gray to yellow. In fact, the yellow-gray canker has started to invade the snow-white sapwood.

7

This is an excellent view of how the canker formed layers of waxy material. The bark on the right of this diseased area is growing spores.

The next pictures show several other areas under the bark. The green phloem layer has pretty much been destroyed, being replaced with a variety of cankerous material. Compare these pictures to the relatively healthy tissue shown in picture 5.

8

This picture shows that the canker has almost completely destroyed the phloem, replacing it with a waxy material and air gaps. Furthermore, the canker is now growing into the xylem and is growing particles on the surface of the bark.

9

An area of mass destruction caused by white canker. The phloem layer is virtually unrecognizable, having been almost totally consumed by white canker, which here appears as light gray in color.

In Summary, while the leaves on this tree may indicate an anthracnose infection, the tree in fact has a much more severe white canker infection at its root. The evidence of this is only barely hinted at by the dryness and curling of the leaves. Even a microscopic leaf surface examination shows little evidence. A leaf cross-section gives stronger evidence of white canker. But by far the best evidence of white canker is a 400x microscopic twig cross-section, where the ongoing destruction of the tree's phloem tissue is plainly evident. Since the phloem layer carries the nourishment for the tree, the white canker is effectively choking the tree of the food needed to live and fight off disease.

This is one of my neighbor's trees. It became diseased about 4 or 5 years ago and was quickly going downhill. For the pior two years it was treated with a fungicide and recovered nicely. At this point in time (early June), no fungicide treatment had been applied, and the tree was again in decline.

1

The lack of a fungicide treatment during the first part of this summer has caused many of the leaves to turn color and fall off. This picture shows one of these leaves. A microscopic look at the leaf showed some white and yellow spores, but not many of them. It's possible that this tree is suffering from white canker and anthracnose.

2

This picture shows a small diseased branch that was near death. It's easy to see why this branch is sick - the bark is loaded with pale yellow white canker spores.

3

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This is a microscopic close-up of one of these spore patches. Several white spores at the top of the picture still have their embryonic white tissue between their lobes, indicating that the spores are under construction (blue arrows).

4

→ ↓ →

Since the branch shown in picture 2 was only about 3/4 " thick, I used a side cutter to clip off a clean end, and then scanned it at 2400 dpi, as shown here. At first glance, there is nothing unusual here. But look closely (click on the picture) at the upper-right junction of the xylem and phloem (blue arrow). The tissue layer there has thickened and turned into a waxy-looking substance. The same thing has happened to the bottom (blue arrow). Furthermore, the phloem under the bark in these two areas has developed voids, with a void also forming between the phloem and the outer bark. Continuing on, the bark between these two areas is so badly diseased that it has decayed and turned a dark brown. In the middle of this decayed area the bark has split, turning the xylem underneath it brown in color (red arrow). This cross-section is an excellent tutorial on the damage done by white canker.

5

This is a microscopic view of the pith at the center of the branch. It has a frothy, bubbly look. This is normal. So far, I've never seen white canker infect the pith.

6

When I examined some "good" surface bark with a microscope, I saw what appeared to be white spores just under the surface, along with a few hypha, as shown above.

7

Picture 4 seems to show that the outer tree rings have been replaced by a waxy substance. This picture shows what this substance looks like when viewed with a 400x microscope. It appears as if white canker material is replacing the original woody tissue.

The wrinkled leaf gave a hint of white canker infection, while its discoloration hinted at anthracnose. The abundance of light yellow spores on the bark was a strong piece of evidence, confirmed by the microscope picture of the spores themselves, which were identical in shape and size to white canker spores. Finally, a 2400 dpi scan of a branch cross-section showed how this branch died: the white canker consumed the phloem layer, preventing nutrient transport. The voids created under the bark cut off nutrients to the bark, causing it to decay and split.

This Red Maple tree in my back yard had been sick with white canker and in decline for several years. At this point (mid May) it was 80% dead.

1

This picture was taken about 20 inches from the tip of the branch, and shows the spores clustering at the branch junction and at the leaf scars, with very few spores in-between.

2

This area, about 3' from the branch tip, shows a large spore population. At this location the spores are more diffuse along the branch. But the total population of spores is larger, making this maple an efficient transmitter of white canker.

Notice also the new leaves sprouting near the heavy spore infestation. The leaves are already misshapen and dying at the edges. One is turning red, as if it were fall! (This picture was taken in mid-May, 2008)

3

Here is a cross-section of this branch, showing the disease infection channels.

The following set of pictures were taken in late September, after the spores had dispersed.

4

It's obvious when looking at this leaf that it is in very bad shape.It's parent tree is already about 95% dead. The straight edge was made with a razor blade for the purpose of making the cross-section views shown below.

5

Here there is white canker on the outer bark, although in this case the white canker is actually transparent and looks like ice. (400x)

6

Here there is white canker under the bark and on the bark. Some is milk white and some is transparent. The tubular form is almost always transparent. (400x)

7

The inner bark is almost completely destroyed by canker. The gray blur in the lower right is out of focus since it's too close to the camera. (400x)

8

The gray blur in the prior picture is in focus here, and is shown to be composed of transparent white canker hyphae. (400x)

9

Here the white canker has eaten away all the inner bark, leaving a void. Note where it is working away at the top of the picture. Also, the outer bark is riddled with canker. (400x)

10

White canker hyphae are under and on the bark, sprouting white canker growths along the hyphae. (400x)

↓ ↓ ↓

11

Here is a long white canker hypha growing on the bark. It at first appears like an icicle in the shape of a ribbon. If you look carefully, where the big bend takes place, there is a small spore branching off (yellow arrow), and another long growth (blue arrow) snakes over the bark to the canker just to the right (red arrow). (400x)

12

White canker under the leaf and in the leaf. (400x)

13

The canker infection has made a real mess of this leaf. The red color is emerging fall maple leaf color. (400x)

↓

14

A dead portion of th leaf that has a large blob of white canker material on the bottom. This canker is spawning a hypha that starts off white and then turns transparent. This hypha is budding off a young spore (red arrow) (400x)

15

This piece of tissue torn from the leaf contains both white and gray canker material. (400x)

16

There is a white canker blob on the left, which looks kind of foamy. The pink surface canker may be due to the leaf changing color in its stressed areas first. (400x)

These pictures are of a 30' red maple tree in my back yard, and are cuttings less than an hour old. I happened to be doing some pruning on this tree and my eye caught these tan discolorations on the branches that were about one-fourth to one-half inch in diameter. All these branch discolorations covered only about 20 degrees of the trunk circumference, and were at the bottom (ground facing) part of the branch. Since this was late May, insect and other disease damage was almost non-existent.

1

One branch had a twig sprouting from it, and that twig had about 5 leaves. One of these leaves (shown here) had the typical white canker characteristics I'd seen in prior years - puckering. The puckered half of the leaf also had yellow spots.

2

This picture, taken with a 2400 dpi scanner at the end of May, shows the junction of this leaf's twig to its branch. The yellow substance is actually a massive quantity of tiny light yellow spores. Even though the twig bark under the spores is very young, it is cracking.

3

As I continued to prune, I noticed many more of these yellow spore patches. As in this picture, these dense patches were consistently at branch junctions and on the side of the branch facing down. (While my unaided eye saw them as simply fuzzy patches, my 7 year old grandson said he could discern individual spores.)

Since I couldn't believe these were all spores, I brought in numerous samples and scanned them with a 400 power microscope. Sure enough - they were all spores, as the following pictures show.

4

These are pictures of the yellow spore patches taken with a microscope. At first glance, they may resemble a lot of teeth. Or, the cleft separating their two lobes may remind one of 3D "Pac-men". If you zoom in for a closer view, you'll see that each spore is milk-white in color, and often has a small yellow object between the two lobes. This yellow object is like an egg yolk, and seems to provide the food for the spore's growth. It shrinks in size as the spore matures.

The several large gelatinous spherical objects among the spores may be germinating spores from another host, since each seems to have a root-like appendage. They may be the "pearls" in the following pictures.

5

6

The pictures shown above are of the spores on the bark of trees. Here we use a 400x microscope to examine the upper and lower surface of the leaf shown in picture 1.

7

This is the top surface of the leaf. The entire leaf looks pretty much like this - nothing much of interest for diagnostic purposes. In fact, except for some yellow spots, you might think this was a healthy leaf.

8

This is healthy tissue on the bottom of the leaf. The white objects are stomata, through which the leaf breathes. Once again, there is nothing visible that gives a clue that this leaf or branch is diseased.

9

This picture shows the bottom of the leaf, near the stem. There are several "yellow blobs" and numerous semi-transparent ribbon-like filaments present.

10

Since the spore density at branch junctions is high, I wondered if the same would be true at leaf vein junctions on the bottom of the leaf. As this picture shows, that indeed is true. There are two types of hyphae present - normal leaf hyphae (round cross-section) and white canker hyphae (ribbon-like cross-section). The yellow objects are embryonic white canker spores.

11

This picture was also taken near a leaf vein. Some of the hypha are brown - possibly they are dying. In addition to the small embryonic light yellow spores, there is a much larger tan globular object present, which could be a germinating spore.

12

This picture too shows a leaf vein on the bottom of the leaf. Hyphae are emerging from the vein and growing embryonic canker spores on them. The two tan globular object may be germinating spores.

13

← →

I included this leaf bottom picture because it shows that these yellow embryonic spores seem to have a tiny attachment "tail" anchoring them to the tree tissue, and sometimes also have a tiny black "eye" at the tip (see the black arrows).

14

Another leaf bottom picture. Here again is one of those tan globular objects that looks like a pearl. Look closely, and you can see the base of the pearl has a hypha which dives into the leaf right next to an octopus-like hypha object. A embryonic yellow spore is also shown, and is connected to a hypha.

15

Another "pearl" object. This picture clearly shows that this object is very likely not an insect egg, since it has a hypha growing from its base, running along the leaf surface, and then diving in right next to one of these "octopus-like" objects.

16

There are two young embryonic spores here - one anchored to the leaf and the other anchored to a hypha.

17

↑ ↑ ← ↓

White canker hyphae tend to be transparent and ribbon-like in cross-section. The two here, growing from black areas of the leaf vein (red arrows), have that characteristic. The width to length ratio of these hyphae can be seen where a hypha twists (blue arrows). It's rare to see a yellow hypha, as in the lower left of the picture.

18

This part of the leaf vein seems to host a whole variety of white canker structures. The "pearls" are there, embryonic spores are present, mature spores are present live hyphae are present, and brown (probably dead) hyphae are also there. In fact, you could say almost all the action takes place on or very near the leaf veins!

After reviewing these pictures, some interesting conjectures can be made:

Except for leaf puckering, a microscopic examination of the top side of a leaf gives almost no clue as to the presence of this disease.
All the microscopic leaf evidence for this disease appears as light yellow spores on the leaf bottom, near the diseased (puckered) area.
The bark may contain a huge number of both white and light yellow small spores (leaf bottoms contain no white spores).
The yellow spores on the leaf seem to take root in it via a small "tail".
"Pearls" often have a hypha coming from them which terminates near a "spider-like" object.
Some filaments are brown in color rather than transparent. These may be filaments that have died.

Silver Maple trees seem to succumb to white canker by losing leaves on their branches from the branch base toward the branch tip. Then even the leaves at the branch tip die. But this seems to be a slow process, taking many years.

1

This part of the branch was about about 15' up a 50' tree whose top canopy was getting very sparse. This branch still had leaves at its tips, so was alive. There are spores present, but relatively few.

2

This branch was totally dead. Note that the spores seem to be present only on one side of the branch, along with some black and green substances.

3

The branch whose junction is shown here was totally dead. It has a large quantity of spores. Usually the spores form in quantities at branch junctions. This branch junction was far more decayed than the nearby bark. It seems as if the branches of silver maples do not produce spores in abundance until they are virtually dead.

While the earlier pictures were taken in late May, the following set of pictures were taken in late September. At this time the white canker had already reproduced by shedding it's spores. Hence, spores were hard to find.

4

This twig cross-section view shows an area that has only a sprinkling of white canker particles, all located between the cortex and the phloem. The bark and dark green cortex are uniform in thickness and neither contains voids. I'd call this a "moderate" white canker infection. It's interesting to note that the white canker particles are located within an area of maximum nutrients (sugars), which are coming from the leaves. (400x)

5

Contrast the relatively "clean" right side of this view against the left side, which contains many blobs of canker material, including a blob penetrating the bark.(400x)

6

White canker is consuming that piece of bark on the left, causing it to lose it adhesion to the twig.(400x)

7

The white canker damage has been so severe here that the entire band of phloem has been eaten away, leaving an air pocket along with tangles of canker mixed with a little of the remaining green cortex. Even the bark has separated from the cortex.(400x)

8

This is what the bottom of a silver maple leaf on this tree looks like. All that white background appears to be white canker on the surface. One long hypha is present (red arrow). Many small hyphae "spiders" are also present, but are difficult to see.(400x)

↓

9

And this is what the top of a silver maple leaf on this tree looks like. While the top of the leaf was generally blemish-free, the particular area shown in this picture shows an exception - a long hypha growing just under the surface.(400x)

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10

This collection of objects appears to be a leaf stem (red arrow) with numerous white canker particles and hyphae directly above it. The canker is probably seeking out the sugars being gathered by the leaf. (400x)

11

This section of leaf is in relatively good shape. The bulging area on the left is a leaf vein. A small piece of canker protrudes above the leaf, and the bottom layer of cells appears to be totally immersed in white canker. (400x)

↓

12

This cut went right through a leaf brown spot about 1/8 inch in diameter. The dark brown spot contained a lighter brown central spot. While "tar spot" disease is common on these silver maple leaves, this was not the typical dark black tar spot. Notice the numerous white canker particles within and on top of the dead spot. Also, note the big blob of canker material directly next to the deep crevice in the middle of this dead spot (red arrow). The circumstantial evidence is strong that this brown spot was caused by an especially strong white canker infection here. (400x)

13

This one of my favorite shots: since this leaf was first bent up, and then a piece was bent down, you can see the leaf's bottom, its inside, and its top - all in one picture. Many of the leaf's cells can be seen since they seem to be highlighted in white canker. It appears that the leaf is about 5 cells thick. (400x)

14

As seen in other leaf cross-sections, canker blobs tend to extend from the top surface of a leaf to its bottom. Here they not only do that, but in three spots they even grow out of the bottom of the leaf! Also, two long hypha can be seen growing near the top of the leaf, just under its surface. The one on the left is budding small canker blobs. (400x)

Variegated maple trees are uncommon but beautiful trees that have a white band around the edge of their leaves. They are a form of Norway maple. Unfortunately, the variegation is due to a virus, which can weaken the tree. The trees often revert back to their natural green color. This particular tree had declined a bit in past years, and this year had lost most of its leaves by the end of August. So it was under more stress than usual. I cut off the tip of a branch and checked it out, starting with the leaf top at 400x.

1

A dead area of the leaf. It looks like white canker may have killed it. It also appears like a tiny strand of white canker is in the upper-right.

2

The white spots here appear to be a white canker infection. Also, the leaf veins, which are mainly green, are starting to turn a bit white.

3

The vein seems infected here, since normally the vein is green in color.

While leaf tops often show a diffuse growth and hint at internal canker growth, leaf bottoms are generally a better indicator of white canker, as these 400x pictures show.

4

The leaf veins, which are normally green, are white here, indicating an infection. Many little white white canker blobs are also seen.

5

Here again, white leaf veins, and many white canker blobs, mainly close to the large leaf vein on the left.

6

No white canker blobs here, but notice that the diffuse white growth seems to be located next to the white leaf veins.

If white canker evidence is somewhat questionable when viewing the top or bottom of a leaf surface, a leaf cross-section can settle the issue since it gives a view into the leaf, as shown in the 400x pictures below.

7

White canker material is visible on the top and bottom of this leaf. White canker is also seen running from the top to bottom of the leaf on the left side of this picture.

b t i

8

A leaf tear and cut make for an unusual view here, showing the leaf bottom (b), the top (t), and the interior(i). White canker particles can be seen on the bottom, while the white canker growth on the top is more diffuse. There is little deep interior white canker growth - it all appears to be just touching the surface, much as an iceberg.

9

This part of the leaf is pretty torn up. But notice the white canker particles in the middle of this picture and the diffuse growths to the right.

The diagnosis of white canker is most easily done by viewing a cross-section of a twig, as shown in the 400x microscope pictures below.

10

Extensive white canker damage is apparent. Many white canker particles are present. The green phloem is almost totally gone, and has separated from the outer bark. The normally somewhat green phloem appears to have been totally killed off and is evolving to a white color. But the xylem still looks good, with open vessels, so the tree is getting water and minerals.

↓ ↓

11

Notice that the cortex here is TOTALLY missing, having been replaced by an air gap. The underlying phloem looks like it too will soon be gone. Note the white canker growth starting in the phloem, going through the missing cortex, and then penetrating the bark (red arrows).

12

The good news is that the white xylem looks great! The bad news is that the green phloem outside of it is half eaten and mangled by white canker. Worse, the cortex is totally dead. Finally, white canker growth is seen on the outside of the bark.

Strong confirming evidence of white canker is the presence of white canker spores on the bark. But, you have to know where to look for them as they reside only in specific locations and are very difficult to spot visually.

13

Much of the twig's outer bark surface looked like this - a light coating of white cankerous material, much like a light snowfall.

14

The final evidence of white canker: the particles themselves on the twig surface, having their very characteristic spore shape. Their embryonic yellow centers are still there, but muted due to age (the color saturation was boosted a bit to more easily see them).

15

While 99% of the twig surface was free of spores, about 1% was loaded with them, and their location was exactly as expected for a white canker infection - at twig junctions. This is a view of one of those junctions. The spore's bleached white appearance and brown centers imply that these spores are old - probably 3 months old.

In conclusion, the shriveled, brown, and dry appearance to the leaves of this tree gave an indication that something serious was wrong. Other visual signs of white canker were not apparent. A microscopic examination of the top, bottom, and cross-section of the leaves gave some supporting evidence of white canker. Much stronger evidence came from a twig cross-section, which showed severe damage to the phloem and total destruction of the cortex. The final piece of strong confirming evidence of white canker came from a microscopic examination of the bark at a branch junction, where an abundance of white canker spores was seen.

With 35 years of growing experience, I've found that Mulberry trees seem resistant to almost any disease. Not to white canker, however. The leaves shrivel, develop black spots and die. Then the branches die.

1

The quarter-inch branch in these three pictures no leaves. Note the oval bark fissures in very close proximity to black bark. Pictures 1 and 2 show spores in the node (branch junction).

Picture 3 is of a leaf scar located about 15" from the branch tip. The area around the scar is filled with spores. Away from the leaf scar, the spores lie mainly on top of the black (and presumably diseased) bark.

2

3

4

5

6

Pictures 4 and 5 are of a branch that still has leaves and fruit. The branch shown in picture 4 is closer to the branch tip, and the one shown in picture 5 is about 15 inches from it. Newer growth appears more disease-free than older growth.

Picture 6 shows spores growing on the branch as well as at branch junctions. The spore cluster locations generally seem to be from 6 to 20 inches from the branch tip, which seems fairly typical for white canker spore production.

While the preceding pictures were taken in late May, the following set of twig surface pictures were taken in late September using a 400x digital microscope.

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7

This bark surface area near the branch junction contained a fair number of spores. Of interest here is the spore near the middle that seems to be exposing a yellow inside (red arrow). (400x)

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8

Here are two rare spherical orange objects (red arrow). They are probably associated with the adjacent white canker objects since they have hyphae growing through them. (400x)

9

This area near the twig junction (branch bottom) had a large number of spores. But these may be old spores. There is a lot of semi-transparent light brown hyphae mixed in with them. (400x)

Now that we've seen what the surface looks like, the following set of pictures shows what the twig interior looks like when making a cross-section of the twig using a 400x digital microscope.

→ →

10

There are two items of interest here. One is the spore in the bark cavity (red arrow). The other is the spore below it (blue arrow), which seems to have a light yellow shroud over it, indicating a yellow spore may be evolving into a mature white spore. That may be true of the spore in the cavity too, although the yellow material seems to have "spilled out" (a birth defect?).(400x)

11

There is a massive hyphae presence in this twig tissue. Plus, the green cortex is very fragmented.(400x)

←

12

Here there was a significant white canker infection, and the tree tried to react by building bark tissue around it, causing a growth consisting of of normal bark and white canker. The canker did manage to eat out a void, however. The void, along with a bark presence, apparently caused the canker to emit some spores within the void (red arrow).(400x)

13

More evidence of where a white canker infection tried to push through but the tree fought back trying to enclose it. (400x)

↓ ↓ ↑

14

There are three components of white canker present here: a light gray blob (red arrow), a yellow compact object (blue arrow), and a semi-transparent mass of spherical objects (green arrow). (400x)

→ ↓

15

When making this twig cross-section, the razor apparently cut through a blob of white canker (red arrow), showing a snow-white shell, a gray inner hollow, and some dark material spilling out. But look carefully around the outside of this white shell and you can see 4 or 5 budding yellow fingers (blue arrow). These buds may be an attempt to generate new spores, due to the presence of bark close by. (400x)

While the wood of the tree is an excellent diagnostic tool for detecting white canker, the leaves can also provide substantial supporting evidence. The following set of pictures deals only with the leaves. All pictures were taken using a 400x digital microscope.

16

The leaf top was littered with these strange circular objects. Curiously, the center of them was white surrounded by a ring of brown. One had two white dots in the center. They can't be stomata (breathing pores), since stomata are found on the bottom of a leaf. (400x)

↓

17

More of these mysterious round objects. But look carefully at the one near the center (red arrow) - it seems to be sprouting a new clear hypha near its top-center. One near the top seems to be doing the same thing. (400x)

18

More of those olive-green circular objects. But there is a fair amount of white canker also present, and, as I've seen before, it seems to like to congregate near leaf veins (where the nutrients are). (400x)

Not all the action takes place on the top of the leaf. Usually, the bottom of the leaf is more informative about white canker symptoms than the top, as shown in the following pictures, which were all taken using a 400x digital microscope.

19

There is a diffuse blob of canker in the middle of the picture, and a more concentrated area in the upper-right, over a leaf vein. Most of the leaf bottom was like this - not much canker visible. (400x)

20

At first, I wasn't going to include this, but decided to anyway because I now believe it says something significant. Canker hyphae and spore generation seem to be enhanced near the surface (epidermis) of a leaf vein or near the the surface of bark. (400x)

21

The leaf veins often had hyphae coming off of them. I suspect this was canker hyphae, but I'm not sure. The presence of these spores close to the vein and hyphae lend support to the belief that the hyphae are canker related. (400x)

22

The interesting thing about this rather poor image is that a "hair" coming out of a leaf vein has a yellow blob attached to its end. Hence, its probably not a normal leaf hair, but a hypha of white canker that may be giving birth to a new spore. (400x)

The analysis of the leaf wouldn't be complete unless we had a peek inside the leaf. The following pictures show this via a cross-section. Once again, these pictures were all taken using a 400x digital microscope.

23

The big blob of canker is growing among the leaf tissue cells, almost completely engulfing a part of it. (400x)

→ ↑ ↑ ←

24

The item of interest here is that dark sphere (red arrow) in the middle of that big blob of canker. There are also three other smaller yellow spheres (blue arrows)present. (400x)

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25

This is a torn leaf section. Are these dark circular objects (a red arrow points to one) stomata, the pores that a leaf breathes through? Some of them seem to have a significant amount of canker around them. (400x)

This Red oak sits on the corner of our lot and has been decline for several years. Two years ago a bark sample from this tree was sent to the Cornell plant pathology lab, and a diagnosis of a Phytophthora was returned (species unknown). The following pictures were taken in late May.

1

This live oak branch is also about 1/4" thick. The top branch junction was just 6" from the branch tip, with no spores between it and the tip. The spores are so thick at the branch junctions and leaf scars that the area appears almost crusty.

2

This cross-section of the branch shown in picture 2 was made with a 2400dpi scanner. The black spot appears to be a disease infection channel. The spot's location suggests that this tree became infected about 5 years ago (around 2003), which is about when I started noticing disease symptoms on almost all of my trees and shrubs.

3

This is a dead branch from the red oak tree in decline. Not only is there a high spore density at the branch junctions and leaf scars, but the spore density is moderately high between these points too, making this tree a prime transmitter of disease.

This branch segment was about 1/4" thick, and was located 12" from the branch tip. There were virtually no spores from this point to the branch tip.

The following set of pictures wase taken in early October, using a 400x digital microscope. Since I believe the spore release took place shortly after the above pictures were taken, I didn't really expect to see many spores left. The first two pictures are of the top of a leaf.

4

Adjacent live and dead spots on the leaf top. The dead spot looks like it could be made up of white canker particles.

5

In general, a pretty boring leaf top surface. As shown here, there were scattered small pieces of white canker, and a few of these spider-like objects.

Since it's just as easy to check the leaf bottom as the top, the following pictures show the bottom of the leaf at 400x.

← ←

6

The leaf bottom had numerous spider-like objects scattered about its surface. But perhaps of even more relevance was the presence of white canker spores (red arrows), along with their visual characteristics. The one at center-bottom appears halfway through its embryonic stage, since it's about half yellow in the center. The one on top is almost through its embryonic stage since there is only a bit of yellow showing through its two halves.

← ← ← ← ← ←

7

The spores and spider-like objects get more numerous the closer you get to the leaf's stem. This view is next to the stem. Of interest here is the variety of development stages of white canker spores. One (red arrow) is pure yellow and just starting to differentiate. Three more (blue arrows) are about half-yellow and hence half developed. Another one (yellow arrow) is almost totally developed, but still has a yellow stalk. Finally, one (green arrow) is fully developed and totally white.

←

8

This is another area of the leaf, close to the leaf vein (in the upper-left corner). Notice the group of developing spores (red arrow) right next to a "spider" object. Each spore is about half-way through its developing phase, still having a yellow globular mass within its two halves.

White canker often likes to hide within the body of a leaf. The following set of 6 pictures check out that possibility via leaf cross-section views at 400x.

↓ ↓ ↓ ↑

9

There are two patches of white canker near the center of this picture that run from the top to the bottom of the leaf (red arrows). But note the internal gray blob of canker that seems to be giving rise to the spore on the bottom of the leaf (blue arrow). There is also a trail of canker (yellow arrow) from this spore to the right and then up to the top surface of the leaf, where there is another particle of canker material.

↑ ↓ →

10

The left-center part of this leaf's cross-section is of the most interest, as there is a long "tail" of canker descending from the leaf's bottom (red arrow). But where this tail enters the leaf, it gives rise to two spores, one of which appears to be cut in half (blue arrow). The stream of canker then continues on left to the top of the leaf. Again, check the spores - it appears as if one has a white root which intersects with the gray canker blob. The intersection forms a tiny yellow spot (yellow arrow). The question is... did the canker give rise to the spore, or did the spore land on the leaf, infect it, and then give rise to the canker?

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11

This spider-object appears to have a root (red arrow) going directly into the leaf. The leaf tissue disturbance hints that the root goes all the way through to the top side, emitting a green blob (blue arrow) on that surface.

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12

There are internal blobs of white canker material on the right and left, that are connected by a tube of white canker (red arrow). A leaf bottom view wouldn't show this, and a leaf top view would only show two small disconnected white spots. This cross-section shows there is a lot of canker within the leaf that isn't visible.

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13

A side view of one of those spider-like objects. The twisted shape and aspect ratio of the top projection (red arrow) match those of the hyphae of white canker.

14

This is a cross-section of the area around a leaf vein. Going by past experience whereby light-gray-translucent and clear material is canker material, this leaf vein is about 80% consumed by white canker. It's not enough to kill the leaf, but it is enough to weaken it severely.

The above set of pictures make a strong case for a white canker infection. But experience has shown that twig cross-sections provide the best evidence for white canker infections. The next set of 7 pictures are all cross-section views made with a digital microscope at 400x.

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15

A good solid confirmation of white canker infection. Particles of white canker have invaded all of the phloem. A patch of canker has colonized the bark (red arrow), but the tree has grown wound wood around it, sealing it off. Two rays appear infected (blue arrows) too, transmitting the infection to the xylem in the center of the tree.

The above set of pictures make a strong case for a white canker infection. But experience has shown that twig cross-sections provide the best evidence for white canker infections. The next set of 7 pictures are all cross-section views of a 1/8 inch twig made with a digital microscope (400x).

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16

Once again, most of the phloem has been infected, and it has been so weakened that the bark is separating (red arrow) from it. The bark is also infected, so much so that it is turning white (blue arrow).

17

White canker has so infected the phloem that it is beginning to shrink and disappear. The canker is also now spreading into the xylem, destroying it too. And it has even managed to jump to the outer bark, replacing it with clear white canker.

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18

Very severe white canker damage is shown here. The green cortex is heavily infiltrated. The bark in the lower-left corner has been eaten away and replaced with canker (red arrow). The phloem, where it meets the xylem, as turned to a waxy light gray-green color (blue arrow). All this canker growth has caused expansion, separating the outer bark and causing the xylem and phloem to separate (green arrow). Lacking nourishment, the xylem will no doubt weaken and die. The branch will then become brittle and easily break off.

19

This really isn't a true cross-section, but about a 20 degree slice into the side of the twig in order to get a better idea of the true shape of this canker. As seen here, the canker appears as cloud puffs along a string (probably a hypha, actually) that runs mostly parallel to the twig axis. Each tiny puff is probably a killed tree cell.

20

This view is even further along the 20 degree razor cut. It's clear that the canker much prefers the green phloem layer, but also grows more weakly and diffusely in the yellow xylem wood.

21

This picture continues further down to the interior of the twig along the 20 degree (to the twig axis) cross-cut. Most of the center of the picture is the xylem, and the "puffs of white" have turned to mostly streaks of white. That's probably due to the infective hyphae being channeled along the vessels of the xylem, using them as a sort of "road" to infect other tree tissue.

In summary, while white canker is present in the oak leaves of this tree, the leaf surfaces were only marginally helpful in diagnosing this white canker infection since the vast majority of the canker lies within the leaf. Therefore, a microscopic view of a leaf cross-section more clearly shows the white canker infection. Nevertheless, the best diagnostic evidence is obtained by examining the cross-section of a small twig. There the infection is concentrated just under the bark, at the junction of the light green phloem layer and the dark green cortex layer. The white canker substance is easily seen there since it disturbs the natural growth so much.

This large red oak stands right in front of our house. It probably is 20 inches in diameter and is about 60 years old. Yet for the past 5 years it has been in decline. More branches die every year. The bark has developed fissures and cankerous material is pushing out of a large vertical split. These pictures were taken in early June.

1

The branch junction shown here is from a quarter-inch diameter live branch, but one in decline. This junction was the first branch junction from the tip of a branch (18" in) and was about 10' high. The entire branch was completely clear of all signs of infection except for the center of the branch junction facing the ground, where there was a high spore population, as seen here.

3

This is a 400x picture of that area in picture 1 having a high spore density. At this magnification it is evident that the light yellow coloring of the spore patch is due to many milk-white mature spores sprinkled with yellow embryonic spore tissue. (Note: a major white canker spore release took place a day or two later.)

4

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Here's another picture taken within that same spore patch. The blue arrow points to what may be an embryonic spore evolving into a mature white spore (the black spot on it may be indicative of the transformation taking place). The picture also shows something very common on infected leaves - a white spider-like object that appears translucent. This spider object appears to have a some spores associated with it (green arrows).

5

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Here is another interesting picture from that same spore patch. The green arrows appear to show two places where embryonic yellow spores are currently transforming into mature white spores. Note the black spot on the side of one of the white spore hemispheres.

2

This 3/4 inch diameter branch segment was about 6' from the Branch Tip. While this segment hosts an enormous number of spores (click the picture to get a close-up view), these spores seem to be concentrated at the branch junctions on one side of the branch.

6

When oaks are badly infected with white canker, they will often develop a vertical protruding canker that runs from a foot or two above the ground to about the 6 or 7 foot level. This oak had such a canker. Using a chisel, I chipped off a piece of it measuring about 1/2 by 3/4 inch. Physically, the canker piece seemed to have the texture of weak particle board. This is what it looked like when placed on a scanner and scanned at 2400 dpi.

7

This is what the surface of that chunk of canker material looks like under a 400 power microscope. Note the big white blob of cankerous material under the bark.

8

This is what the interior of that chunk of canker material looks like under a 400 power microscope. It is a waxy, translucent material, and seems to be a mixture of wound wood and white cankerous substance.

This neighborhood White Oak didn't look healthy at all. So I clipped a branch from it and decided to check it out microscopically. The branch sample was obtained in late September. The results are shown below.

1

This tangled mass of canker material is pushing out the outer bark, which is also riddled with canker. The canker material ranges in color from tan to white. (400x)

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2

Note the "D" shaped void (red arrow) - probably caused by the pressure of the surrounding canker growth. The canker outside the void is thicker than the inside, which probably pushed it out further than the inside could push in. Plus, the green sapwood appears riddled with white canker particles. (400x)

3

The mangled sapwood tissue in this view contains canker material plus lots of hyphae. Even bark surface canker can be seen. (400x)

4

There isn't much left of the green sapwood. Two thick bands of canker growth have expanded to the point where they both left "D" shaped voids in the wood. And one bundle of crystal-clear hyphae reaches up through a void and spreads out. (400x)

5

The canker growth here is a mixture of solid canker and hyphae. (400x)

6

When doing a twig cross-section, I had always wondered if the small white circular blobs were really spherical or the ends of a circular tube. This view was taken with a razor cut of about 10 degrees from the twig axis. If the blobs were really tubes, we would see many long ovals. Instead we still see circles, meaning that the small white blobs are really pretty spherical in shape. (400x)

7

A good leaf cross-section view that shows two different kinds of canker material. The large blob at the top is mostly filmy and transparent, while the blob at the bottom is more gray in color. Canker that is separated from leaf material tends to be snow white or transparent. (400x)

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8

A good view of a leaf cross-section showing both the inner chlorophyl (blue arrow) and the leaf bottom that is covered with this white canker material. The surface rip in the leaf bottom (red arrow) shows how dense this canker material is, and how completely it covers the leaf bottom, probably choking off the leaf. (400x)

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9

This leaf cross-section view also shows us some of the top of the leaf. The two blobs of canker on the top resemble bubble-wrap (blue arrows). Click the picture to examine the left one in detail - a hypha came up through the leaf and its tendrils engulfed some leaf cells, digesting them. A chunk of gray canker (red arrow) material sits on the leaf at the left of the picture. (400x)

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10

Here again the leaf bottom is covered with a dense coating of white material, and the top is also covered. But the shapes and transparency of the canker differs. A leaf vein (red arrow) is on the left. (400x)

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11

The bottom of this leaf is totally covered with what looks like white canker. A vein is on the left. The leaf top supports numerous clear canker material (the red arrows points to one blob). (400x)

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12

I'd always wanted to cut a leaf through its inside so I could see between the sides, as in removing the slices of bread making up a sandwich. By luck, the razor I used to make this cross-section tore open the leaf for me here! A long canker hypha can be seen (red arrow) running along the leaf, and then continuing on out of the leaf. Apparently it is more cohensive than the leaf cells. The bottom of this view is the leaf bottom (400x)

As the pictures show, there is no question that this white oak is severely infected with white canker. The extent of this infection makes one realize how tough trees are. And, this severe infection did illustrate several additional details about the white canker disease.

While there are a variety of flowering trees in our neighborhood, in my opinion the most beautiful one is a flowering peach on a nearby street. Every year its a joy to look at when in full bloom. But the tree seems to be in decline. The peaches it products are small and stunted. Curious as to why, I snipped off a branch for analysis. The sample was taken in mid October. The pictures below were all taken with a 400x digital microscope. We begin with pictures of leaf tops.

1

The faint white spots hint at the particles of white canker present within the leaf. But there appears to be no white canker material on the leaf surface itself.

2

The white spots hint at the particles of white canker present within the leaf. These spots don't seem to break the leaf surface, and they seem to cluster near the leaf veins.

White canker often shows a preference for leaf bottoms, which are shown in the following set of pictures, again at a 400x magnification.

3

Once again, the white spots hint at the presence of white canker particles within the leaf.

4

More white spots hinting that there are white canker particles within the leaf. There seem to be more of them on the right side, which appears a bit less healthy.

5

Look carefully at these white spots, and you will see that they have the general appearance of white canker spores. The red bar is 50 micrometers long, about the diameter of a white canker spore.

Fortunately we have a means to lift the veil and take a peek inside the leaf: mount the leaf in a vise, slice it along the vise top, and examine this top with a 400x microscope.

6

There is a solid vertical band of canker running through the leaf here, and on the left there are some buried canker spores that were exposed by the cut. The red bar is 50 micrometers long, indicating that the spores are about 30 micrometers in diameter.

7

By good fortune, the razor partially tore off a small piece of leaf surface and bent it up, showing us that there is indeed a thin layer of extensive canker growth just under the leaftop surface. The cross-sections hint that there is a thin band of canker, but this picture actually shows it. Notice that the bottom leaf surface also shows some canker patches. Perhaps bottom surface views don't show it due to its thinness and transparency. Only edge views like this bring it out.

8

There is a band of canker running from the top of the leaf to its bottom in the center of the picture. More important, though, is that this picture shows that the canker generally forms a thin layer just below the top surface of the leaf, and also a slightly more diffuse layer just above the bottom surface of the leaf. Together they show why, while white canker is extensively present, viewing the top or bottom of a leaf may not show much of it.

In general, the best means to determine the presence of white canker is examine the cross-section of a twig at 400x, as is done in the following set of pictures.

9

White canker is killing this area. Note that the split in the green cortex begins at a particle of white canker. A blob of white canker is growing just to the left of it, blocking a vessel.

10

This picture shows a heavy white canker infection just below the surface of the bark. But the green phloem so far doesn't seem to be infected badly.

11

The extensive growth of white canker just under the outer bark is consuming it and killing the outer surface, turning it black. The green cortex under it is starting to get attacked and is developing some voids. Under that is the nutrient transporting phloem layer. Its spongy yellow appearance seems to indicate it is dying. The only thing in good shape is the snow-white xylem in the lower-right part of the picture. So the tree can still transport water and minerals up from the roots, but nutrients generated by the leaves are having a hard time getting around. That would explain why the peaches produced were stunted in their growth.

Now that we've seen inside the bark, let's look on the outside. The first view, like the others above, is at 400x. Typically, top-of-the branch bark views such as this show little of interest.

12

Note the lack of spores on the upper surface of the twig. But it does appear that there is a thin layer of canker there that has split, possibly due to underlying canker growth.

In contrast, if a tree is infected with white canker, the bottom of branch junction near the branch tip is often a hotbed of spores. To the naked eye, such an area looks like gray dust. This junction was located 12 inches from the branch tip. These are 400x views of the bottom of this junction.

12

Note the lack of spores on the upper surface of the twig. But it does appear that there is a thin layer of canker there that has split, possibly due to underlying canker growth.

In contrast, if a tree is infected with white canker, the bottom of branch junction near the branch tip is often a hotbed of spores. Unfortunately, these spores are barely visible to the naked eye. This junction was located 12 inches from the branch tip. These are 400x views of the junction bottom.

13

This is a view of the bark on the bottom of a twig, about 1 foot from the twig tip. This is the usual spot where spores form. Note that there isn't a single yellow embryonic spore present here, indicating that these are old spores. This wood was created two years ago. The red scale bar is 50 microns long, so these spores are about 40 by 50 microns in size - identical to those on other trees affected by white canker.

14

Another view of spores on the bottom of a twig node (branch junction), where they seem to gather. To the eye, these spots appear as a barely visible gray patch, almost like fine dust or dirt. It's sooo easy to pass them off as that!

15

One of the densest patches of white canker spores I found at the twig bottom node. Of particular interest here is the gray-brown stuff oozing from the "mouth" of many of the spores. For some reason these spores did not release, and are sending out hyphae to infect itself! (The roundness of the twig makes it difficult to focus on all parts of the field of view here due to limits on the depth of focus of the microscope.)

In summary, this beautiful flowering peach is moderately infected with white canker. Except for general tree decline and mild bark fissures, all the strong evidence for white canker comes from the 400x microscopic views described next. Although the leaf bottoms and tops show only faint white particles, a leaf cross-section view shows internal canker growth, mainly in thin sheets near the leaf surface. As usual, stronger evidence comes from the examination of twig cross-sections. There we see strong white canker growth consuming the inside of the outer bark. The phloem is also taking a beating. Further strong evidence comes from the bark surface, at branch junctions. As in other infected trees, there are no white canker spores on the top (upside) of the branch, while there are abundant spore patches on the bottom (downside) of the branch. Their pure white color seems to indicate they have been there for some time (they lack the young embryonic yellow tinge).

White pines are one of the most numerous native trees in this area. Yet, it's sometimes difficult to determine whether or not they have white canker infections. Since I've noticed a number of white pines whose needles are turning brown and dropping off, I decided to check a few out. The following white pine was in decline, and probably dying. This sample branch was taken and analyzed in early June.

1

As you can see here, there are some green needles, and some that have turned yellow and died. But unlike other tree species, there are very few spores along the branch or at the branch junction.

2

The telltale spores and hyphae are actually there, but difficult to see. As shown in this 400x microscopic view, the hyphae appear as "cotton-like" tiny areas at the point where the 5-needle packets erupt from the bark. The spores are scattered throughout the hyphae.

3

These spores were on the base of a needle. (400x)

I returned to this tree in early November, after the old needles were shed and the new needles were created. I snipped a branch and put it under the microscope. The needles visually looked fine and there was no evidence of white canker when looking at their cross-sections. Likewise, very few spores were found on the surface of the twig bark. Finally, I examined the cross-section of a twig. The results are shown below.

4

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Look closely and you can see a diffuse blob of white canker in the upper-left corner. Also, the lower-right corner shows another more concentrated blob of white canker that is shooting a runner toward the bark, then under it, then breaking the surface, then creating a blob above the surface.

5

A small side branch was pruned off, and the scar on the larger host branch was examined in this picture. Note the canker's preference for rich green tissue, and the diffuse nature of the white canker growth.

6

Two things of note here: 1) The white canker grows near but avoids the large vessels. 2) The blob of white canker between the vessels is very likely the source of the white canker area on the bark near it.

7

White canker in the outer cortex, and at the xylem-phloem junction. The proximity is probably more than a coincidence.

8

Once again, the canker growth is near a conducting vessel, but does not enter it. And this canker area has spawned some translucent canker on the bark surface.

White canker appears to have a difficult time infecting white pine trees. The needles and bark show little or no evidence of an infected state. While microscope views at 400x of twig cross-sections will reveal the white canker, its appearance is often diffuse, and it clusters near the sap transporting vessels. But something in these vessels or sap keeps the white canker from attacking them. This is very different from deciduous trees, where white canker seems to know no bounds. Hence, it appears that white pines will stand up to a white canker infection longer than deciduous trees

I located another nearby large white pine whose needles were also half gone due to disease, and obtained a sample branch from it. These pictures were taken in early June, just about the time of a major spore release. The analysis results are shown below.

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1

This is a branch from that diseased tree. It fits the typical profile of white canker: moderate spore density scattered on the branch bark with a high concentration at branch and leaf junctions that are on the bottom of the branch (red arrow).

2

3

Here are two pictures of the yellow spore area pointed at by the red arrow in picture 1. They were made using a 400x digital microscope.

4

This is a single spore and its likely associated hypha just under the Bark. This picture was also taken at 400x.

5

Here is another 400x view of an area of the bark that contains both spores and hyphae.

6

This appears to be a massive hyphae tangle along with a number of spores in the background. This is a 400x view.

I went back to this same tree in early October to get another branch for testing, with the intent of doing a more in-depth analysis using needle and twig cross-sections using a digital microscope. We begin by looking at the surface of a needle from a 1/8 inch twig.

7

Here is a plain, generic needle surface. Only tiny pieces of white canker evidence are present, like at the center-left, and they would probably be easy to overlook.

8

This needle surface shows more white streaks of material that is probably white canker. Interestingly, near the top it almost looks like overexposed words!

9

This is probably a white canker infection on the needle surface, but it almost resembles snow because of its diffuse pattern.

10

The stomata on the surface of a needle. It's unclear if the white stomata and the white surround are actually due a white canker infection, since I haven't found any closeup views of healthy white pine needles to compare against.

11

These stripes seem to be common on many needles. But they aren't always as uniformly spaced as shown here.

12

Prior pictures have shown these stomata in separate rows. Here two rows are grouped together. That may be just a chance occurrance. But I'm guessing that the white stomata and the white surround are due to white canker, although the evidence isn't as strong as I haven't seen this infection pattern on other needles or leaves.

The following set of 400x microscopic pictures shows cross-section views of several needles. Like the prior surface pictures, there is some evidence for white canker, but it isn't strong.

13

Not much canker infection shown here. What little there is seems to be on the outside of the needle and within the vacuoles at the needle center.

14

This picture shows a bit more canker infection at the needle's surface and a bit more within the center of the needle. But the needle doesn't otherwise appear badly infected. This agrees with the outward appearance of the needle, which was normal in appearance. Part of another needle is shown in the upper left.

15

Of the needle cross-sections shown, this may be the one showing the worst infection. But once again, the infection sites are the same - the needle surface and the pith at the center of the needle. And once again, big blobs of white canker seem to be absent - all the infection seems to be diffuse.

When needle and leaf surface views and cross-sections aren't very helpful for providing good evidence for white canker, twig cross-sections can be very informative, as shown in the following microscopic views at 400x.

16

Lots of dispursed white canker growth in the phloem, and a big bundle around the conducting vessel. The bark seems to be riddled with diffuse canker. Interestingly, the sap in the vessel seems to ward off the white canker.

17

More evidence of white canker. Also, again note the tendency of the canker to congregate at the outer phloem and near the conducting vessel, where the energy supply is richest, i.e., food is plentyful.

18

Not all white canker is located near the vessels, as this picture shows. Also evident is that the dark green cortex is hard to find - there is so much white canker mixed in with it.

19

There is so much diffuse cloud-like white canker in this area that it almost looks like a work of art. In fact, this may be the prettiest white canker picture of all the trees and shrubs I've examined!

20

This is a great example illustrating that white canker tends to seek out areas under the bark where the food supply is at its maximum - within the phloem and near the vessels (but not too close to the sap, which it seems to avoid).

21

Another area of intense white canker growth, again next to a vessel. Missing is the appearance of more distinct blobs of white canker. The closest we come to blobs seems to be shown here, in or on the bark surface, where grayish blobs are seen.

In summary, it appears as if white pines definitely can be infected with white canker. However, evidence for this infection is difficult to see when examining either the surface or cross-section of a needle. (White highlighting of needle stomata lines may also be an indicator.)

The best evidence for white canker is available in May and early June, when white canker spores are present at certain locations on the branches, and can be examined microscopically. The most reliable year-around evidence is obtained by examining the cross-section of a twig microscopically using a 400 power microscope, where the white canker shows itself as diffuse white patches in the outer phloem, adjacent to the conducting vessels.

This blue spruce was found on the lot of a neighborhood tree several blocks from my home. The tree was about 30' tall and had seemed healthy for the past 35 years. Yet, a year or two ago, the branches on the lower part of the tree began sagging and losing needles, which was typical of other blue spruces in the area. These samples were taken in late May.

1

This picture shows a generally healthy branch tip with green needles and almost no spores. (400x).

2

Progressing toward the base of this branch about 8", more needles are starting to lose their color in spots, and the fungal-like growth and spore density increases. (400x).

3

Here, about two feet from the branch tip, the side branches have lost about half of their needles, and the spores have significantly increased in density. (400x)

While the earlier pictures were taken in late May, the following set of pictures were taken in late September. At this time the white canker had already reproduced by shedding it's spores. Hence, there were few spores to be found.

4

Generally, as shown here, the bark surface contained only scattered light patches of white canker. (400x)

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5

Here is one piece of the bark that actually contains white canker spores, something rarely seen this time of year. However, these look like old spores, as some seem to have ruptured (yellowish stuff on them). The interesting part, however, is the hard-to-see full spore structure. It seems to begin as a yellow oval, change to a white stalk, and then to a brownish-gray tangle which gives rise to a white spore at the tip. See the red arrows. (400x)

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6

The outer bark here is heavily infested with white canker, which has probably replaced 75% of it. The phloem is also almost totally consumed by white canker. This canker has invaded a vessel (red arrow), and two fingers of canker have eaten away an area under the bark at the bottom (blue arrows). (400x)

7

While the outer bark isn't in too bad a shape here, the phloem under it has so much white canker in it that the chlorophyll is almost all gone. Of even more interest is the collection of white canker spores just outside the bark. (400x)

8

This picture could be titled "Canker Galore!", since there is so much white canker and such a variety of its forms. Most white canker seems to take the shape of a foam, reminiscent of bubble-wrap. This may be due to the canker enveloping the plant cells, digesting them, and manufacturing canker food. When the digestion process starts, the canker is gray. When it is complete it turns white to transparent. (400x)

9

This white canker has lodged itself in the bark, making it bulge out. The phloem underneath it is also riddled with white canker particles. (400x)

10

This is a photo merge of 5 needle cross-section photos taken at 400x. White canker infection is evident both near the surface of the needle and around the core of the needle. Hyphae are also present. Click the picture for a big view. (400x)

11

This is a photo merge of 6 needle cross-section photos taken at 400x. White canker infection is evident both near the surface of the needle and around the core of the needle. Hyphae are also present. Click the picture for a big view. (400x)

This blue spruce sits on a corner, with another blue spruce on either side of it. It has been in decline for the past two years, with most of the decline happening within the past year. The branch in the following two pictures has lost about half of its needles. The pictures were taken in late May.

1

If you look closely, you can see some spores, although the density is low.

2

The three needles shown above are diseased and losing color. Again, a careful examination shows some spores. There are also cobweb-like things and some brown spots on the branches.

One reason for taking these needle close-ups was to see if this (and other area) blue spruces were suffering from "needle cast" disease. If they had this disease, the needles should have had black spots along them in late winter or early spring. Earlier checks showed these spots weren't present, and there is no trace of them here. Therefore, its unlikely that needle cast is the cause of this tree decline.

This blue spruce is about a hundred feet from blue spruce #1. Over the past year or two, I had been noticing a severe decline in the health of all the blue spruce trees here in southern New Hampshire. But this one seemed immune to the decline - there were no dead needles and its branches were always held out erect. That was until mid-summer 2008, when I started noticing a sudden and dramatic decline in the health of this tree. It now resembles the others - drooping branches and dying needles. I clipped off a dying branch and put it under the microscope, with the results below.

1

Here is a picture of the lower branches of this tree where the branches are dying. The needles seemed to be exceptionally dry. The pictures below show the likely reason. (The sun was low, and at my back, so you can see my shadow as I took the picture.)

2

As you can see, the phloem and cortex are drowning in white canker. Its in the bark too. (400x).

3

It appears as if the canker growth was so extensive within the phloem that it burst through the bark. (400x).

4

The green cortex is virtually gone, and the outer phloem has lots of canker. But the interesting item here is the presence of the white canker spore on the bark. (400x).

5

The predominant brown color of the inside of this pine needle reflects the fact that it is almost dead. The outer surface is riddled with white canker and the core is half-eaten away. In the upper left corner, where the razor tore off the last bit of needle surface, the ribbon-like material is very canker-like. This is a composite picture. (400x).

6

This is a composite view of another needle only about a quarter-inch from the needle shown in the prior picture. The overall shape differs, and the center is still intact, but the outer surface is almost totally consumed with white canker. Its no wonder that this tree is undergoing serious decline. (400x).

This neighborhood tree has an interesting story associated with it. I was driving by a home and noticed a tree with only half its normal foliage. Since it was a Sycamore, and I hadn't checked these trees, I stopped. The homeowner happened to be in the yard. I'd known him from years ago. I explained what I was doing and he said I could take whatever branch sample I wanted. A few minutes later, a tree service truck drove up. Turns out the homeowner was waiting for him. The homeowner explained that several trees were sick, dropping branches, and wanted them cut down. The tree service guy happened to look at the sycamore, suggested it was in very bad shape, and should be cut down! That sure validated my belief that these trees were sick.

1

Picture S1-1 shows the tip of a branch from this tree. There is little of interest.

2a

2b

2c

2d

These views show the spores that were on that branch. Since this was new wood, I wanted to see what very newly implanted spores looked like. Generally, they were yellowish in color, as in the top picture of the set. The computer's color correction software tried to make them white in the remaining pictures. Their yellow color seems to indicate the yellow spores settled in, and then later converted to white spores. (400x)

3

Unlike other trees, this sycamore tree doesn't seem to have its spores gather around branch or leaf junctions. Instead, the spores congregate on wounds, as shown here.

4a

4b

4c

Here are several close-ups of the spores within that wound. (400x)

5

But the big surprise was a sick looking terminal leaf, a portion of which is shown here. It had a dull look. In fact, it looked hairy. The sickest parts of the leaf had the most hair. (400x)

6a

6b

6c

Here we see that this isn't hair at all, but hyphae, a key sign of infection. This leaf bottom was loaded with it! (400x)

7

The top of the leaf also was filled with these hyphae. But, as this picture shows, nowhere were they thicker than at the stem. (400x)

8

This is a close-up of this stem area. It looks like a tangled jungle of hyphae. (400x)

The super abundance of these hyphae leaves little doubt that this tree is in serious decline, and why the owner may cut it down.

While the earlier pictures were taken in late May, the following set of pictures were taken in late September. At this time the white canker had already reproduced by shedding it's spores. Hence, spores were hard to find.

9

I doubt this this is white canker since this sheet-like covering isn't typical of it. I'm guessing it's some other disease. (400x)

10

Here that bark material resembles a light frost, or thin ice. (400x)

11

This was the best-looking twig cross-section. Note the rich green inner bark and sapwood. There are only a few indications of canker.(400x)

12

Lots of evidence of white canker here: it's growing on the outer bark, a hypha ribbon is present, a white strand is in the green sapwood, and there are voids within the sapwood.(400x)

13

A large blob of white canker has invaded the green sapwood, where it has created a void. A hypha is taking advantage of this void to spread the disease. Even the outer bark has been mostly replaced with canker material.(400x)

14

The blob of white canker has grown so vigorously that it has erupted through the bark. White canker is now even growing in that wound. (400x)

15

The line of tan white canker has so destroyed the integrity of the adjacent bark that the outer bark has lost its adhesion. Without nourishment, it will eventually rot and fall off. (400x)

16

Sycamore leaves seem to have numerous spider-like objects on their surface. This leaf cross-section shows those objects from th side. It also looks like there is white canker material present on the bottom of the leaf. (400x)

17

Seen edge-on, those spider-like objects look like leafless, transparent trees. There are also several white canker blobs showing. (400x)

18

The big white blob is a leaf vein. The tree-like hyphae seem to like being near the vein, probably because its a source of nourishment. (400x)

19

This part of the leaf seems to be heavily invested with white canker. (400x)

20

Top of the leaf. Looks like an infection within the leaf here. (400x)

21

These spider-like objects were scattered all over the leaf top. Yet, they weren't like the kind usually associated with white canker. (400x)

22

The surface of the leaf top looked lightly mottled with a tan color. Examining such an area at 400x showed this view. That color seems to be due partly to these spider objects, but mostly to some infection internal to the leaf. (400x)

This Tulip tree in our front yard was incredibly healthy until a few years ago when white canker hit. This is a dead branch from that tree - one that probably died a year or two ago.

1

The bottom of a branch junction, about 8" from the branch tip. Note the profusion of spores at the branch junction. They apparently killed off the smaller branch, destroying its bark. The spores only seem congregated on the diseased wood - there are no spores on the nearby "clean" wood.

2

In contrast to the bottom of the branch junction, the top of this junction has no spores! For some reason the spores seem to prefer to populate the underside of branch junctions.

3

A close-up of the spores present at the bottom of the branch junction. They are white with a fat clamshell appearance. There are also some young yellow spores interspersed with them. (400x)

4

Another close-up of the spores present at the bottom of the branch junction. (400x)

5

This branch junction is several feet further in. The spores still congregate at the branch junction, but are more widespread on the main branch.

6

This branch Scar from a live branch was about 5' in from the branch tip. There are abundant spores present, but again, in close proximity to the leaf or branch junctions.

7

The center branch is live, but the two side twigs are dead. There are lots of spores around the junctions, and the bark between them is almost solid with spores.

While the above set of pictures was taken in late May, the following set was taken in late September. At this time the white canker had already reproduced by shedding it's spores. Hence, spores were hard to find.

8

While the outer bark was generally free of indications of white canker, this area was like an island of them. (400x)

9

A small area of the bark surface showing some disease symptoms. (400x)

10

This twig cross-section shows canker present both in the bark (yellow) and in the sapwood (white). (400x)

11

This twig cross-section shows canker particles in the inner bark along with a hypha. (400x)

12

The white blob on top is white canker growing in the sapwood, while the light yellow blobs on the left are white canker growing in the inner bark. (400x)

13

The canker in the bark and sapwood have combined and destroyed so much wood that air pockets are actually created under the bark. (400x)

14

It appears that this is a prime example of all the components of white canker: a shapeless white growth, a spore about to emerge, and a hypha connecting the two. It's rare to see all three of these objects together. (400x)

15

Good example of white canker blobs in the leaf (although they look gray). There appears to be an area on the leaf bottom connecting them. Also, it looks as if the razor cut through the canker blob on the left, seeming to show that the canker material engulfs the green leaf cells. (400x)

16

Note the gray hypha with gray canker blobs along it, running along the bottom of the leaf, although rising in the middle of the picture. (400x)

17

The entire bottom of this leaf section looks like it is infected with white canker, and right in the middle is a hypha shooting up through the leaf, creating a spore on the top, and then continuing on the top to generate yet another blob of canker a short distance away. (400x)

18

There appears to be white canker all along the bottom of this leaf. Furthermore, there are canker blobs growing in the middle to the extent that they are pushing the top of the leaf out. (400x)