Testing has shown that fungicide propiconazole is definitely effective in controlling a plant infection due to white canker fungus. But may raise another question as to exactly what happens just after an application of this fungicide, and how long it takes. Since application of this fungicide does not cure the infection, the question then arises as to how often this fungicide must be applied. The problem is that since white canker is a new fungal disease, there is no advice out there to go by.

The obvious measure of success of a treatment is simply to note the external improvement in the health of a plant. Typically, this is done by looking at the appearance of the leaves of the plant. As discussed in a previous section, treating white canker through use of fungicide propiconazole will usually show easily discernible leaf improvement in about 10 days. There may be increased branch growth after that.

While leaf health is a good indicator of plant health, it is more of a "good-bad" measure. Earlier in this website, it was shown that a white canker fungal infection really makes a mess of the interior of the plant. Specifically, the water, mineral, and nutrient transport tissues within the plant are blocked by the invading white canker fungus, choking the plant of the things it needs to survive. Hence, a better indicator of plant health is an examination of the interior of a plant. I've found that microscopic views of twig cross-sections to be an excellent indicator of plant health.

With all this in mind, I decided to closely monitor a single planting in my yard over time to see the effect of a propiconazole treatment. After some thought, I selected our andromeda shrub, for the following reasons:

• Because it was in my yard, it was easily accessible (no treks to a neighbor's yard)
• It had lots of branches to cut samples from
• It wasn't so tall that I couldn't reach the branches (like a tree)
• It wasn't so short that a few dozen sample cuttings would denude it
• It readily showed the effect of a white canker infection
• It was past flowering, so was definitely sprayed (plants in flower weren't sprayed due to concern for bees)
• It wasn't a highly prized planting, so if I accidentally killed it, it wouldn't be a huge loss

My treatment plan was to note its interior health before the first application of propiconazole, and then note its interior health for each day afterwards. My goals were as follows:

• Determine how a propiconazole treatment affects the interior of the plant
• Determine if the standard application of fungicide is adequate
• Determine how long the treatment is good for
• Determine when a successive treatment is definitely needed

To begin with, photo 1 shows a spring photo of the andromeda that I decided to use as a test plant. Photo 2 shows the blossom cluster from this plant.

Photo 1 - Andromeda bush used for fungicide testing		Photo 2 - Andromeda bush blossom cluster

Now that the overall appearance of the andromeda bush has been shown, we can begin to look at it in more detail. The next set of photos, taken on May 1st, can be thought of as an early reference, in the sense that they were taken about a month before the first propiconazole treatment of the year.

As discussed earlier, the white canker fungus usually invades all parts of a plant. Photo 3 was taken with a 400 power digital microscope, and shows a cross-section of an andromeda leaf. The interior should be a deep, solid green. That white material there is all fungus. Photo 4, also taken with a 400x digital microscope, is a view of the bark surface of this andromeda shrub. Those white objects are white canker fungus fruiting bodies. The third piece of white canker evidence on this plant is shown in photo 5. It is also a 400x view, but of a cross-section of a 1/8" andromeda twig. Actually, at a magnification of 400x, only a small part of the twig interior can be seen, so these twig cross-sections are in reality a composite of dozens of these microscopic photos (25 in this case).

Because of the large number of photos making up these twig cross-sections, they contain a lot of detail, so be sure to zoom into them (by clicking on them) to see all available details. Furthermore, clicking on a point within that zoomed photo will usually zoom in even further.

Photo 3 - Andromeda leaf cross-section		Photo 4 - Andromeda twig surface		Photo 5 - Andromeda twig cross-section

Before continuing, photo 5 should be carefully examined. That yellowish center with all the "holes" is the pith, or inner xylem of the twig. It should be frothy white, like soapy water. The area surrounding it is the xylem. It is composed of radiating white streaks here, but healthy xylem should be a solid light green. The phloem layer lies outside of this, and should be a deep green. Instead, it is a very white-green. Those swirls of white are actually white canker fungal growths. And on the very outside is the bark, which should be a nice brown color. But it's either not there or is there but infiltrated by white canker fungus. As the evidence shows, this twig is badly infected with white canker!

The first propiconazole fungicide spraying of the year was done on May 28 by an agent from a local commercial tree and lawn care company. I had a contract with them to do my seasonal pesticide and fungicide tree and shrub treatment. So this became "day zero" of the treatment test. The mix that the agent applied contained the fungicide propiconazole along with an insecticide or two. 96 ounces of propiconazole (3/4 gallon) were applied to the trees (about 17) and shrubs (about 51) planted on my 1/4 acre property. Actually, not all were sprayed, since, out of consideration for harming the bees, only the non-flowering trees and shrubs were sprayed. By "spraying", I mean that the agent sprayed the foliage, and not the ground.

While I judged the health recovery progress of this andromeda bush mainly by taking twig clippings for cross-section analysis, it's important to keep in mind that cross-section analysis is a destructive process. Once that twig is cut, it can no longer be used for another cross-section analysis later on. That in turn means that every twig used for analysis comes from a different part of the bush. Since each of these twigs may have absorbed the fungicide a bit differently, and reacted to it a bit differently, cross-sections taken on successive days should not be strongly relied upon as reliable indicator of fungicide healing action on successive days. Instead, look for general trends over a several day period. Hopefully, at some point in the future, technology advances will enable us to continually monitor the interior of one or more bush twigs without damaging them!

Photos 6 and 7 show the cross-section fungicide treatment results during the first two days. Photo 6 was probably from a mostly dead twig, since the phloem layer is almost totally dead. (The "hole" in the middle is due to a software "stitching" error. Hence, the center photos were not included in the composite you see.) Photo 7 is more realistic of a live twig, as there is green tissue throughout. But note all the whitish swirls and rays - those are white canker fungal growths. The center xylem (pith) should be frothy white, like soap bubbles. But much of it is instead cankerous material.

Photo 6 - Day 1 - andromeda twig cross-section		Photo 7 - Day 2 - andromeda twig cross-section

Somewhat surprisingly, there is a definite improvement in the interior of the andromeda as early as the third day, as shown in photo 6. The xylem now has a definitely greenish look and the phloem has made the same improvement. Photo 7, taken on day 4, shows an even greener xylem, but the phloem is a mixed bag.

While not at all obvious, it's important to note that the white rays radiating out from the center xylem (the yellowish area) are rays of white canker fungus. Now, if you look carefully at that green outer xylem, you will see a halo of a slightly darker green surrounding the inner xylem. Note that the white fungal rays are reduced in intensity in this darker area. What this means is that the fungicide is radiating outward from the inner xylem, and killing the white canker fungus as it proceeds!

Photo 6 - Day 3 - andromeda twig cross-section		Photo 7 - Day 4 - andromeda twig cross-section

The day 5 photos illustrate some important information. The twig cross-section in photo 8 seems to indicate a severe return to a white canker infection. In fact, later testing has demonstrated that this is not the case. I've found that when a twig lies around for hours or days, the green chlorophyl remaining in the phloem and xylem tends to dry up and disappear, leaving only the white canker fungal material behind! That was the case with this twig

Photo 9 shows the partial cross-section of an andromeda leaf. As mentioned elsewhere on this website, white canker tends to invade all parts of a plant, even the leaves, where it will also try to reproduce by sometimes creating small (50 micron diameter) fruiting bodies on the surface of a leaf. These fruiting bodies are always white, close to the color of a tooth. But note that the fruiting body shown here is brown, which seems to indicate that this fruiting body was killed by the infusion of the propiconazole fungicide. If this object were a pollen object sitting on the surface, it would not have changed color. Also, note that underneath this "dead" fruiting body (within the body of the leaf) lies a reservoir of white canker.

Photo 8 - Day 5 - andromeda twig cross-section		Photo 9 - Day 5 - andromeda leaf cross-section

The day 7 photos illustrate some additional interesting information. All these cross-sections were of different twigs, but sampled on the same day. These photos illustrate how different the twig interiors can be, even though they were taken from the same shrub on the same day.

The twig shown in photo 10 is probably the "cleanest" of the lot, while the twig shown in photo 11 shows a huge amount of phloem and bark destruction due to white canker. The twig shown in photo 12 is somewhere between the two.

The twig shown in photo 13 is especially interesting. It is the first twig where I decided to make the cross-section at a leaf junction. Past experience has shown that white canker fruiting bodies tend to congregate at branch or leaf junctions. Here, the leaf junction is on the right. And, as expected, the area around this junction is riddled with white canker blobs. Furthermore, the white canker in this area appears to be getting killed off, due to its brown color. Equally interesting, once again, is that greenish halo around the center pith. It indicates that a wave of fungicide is radiating outward from the pith, killing the white canker fungus as it migrates outward. But probably the most interesting thing shown here can barely be seen. If you carefully examine the upper-left phloem layer, you will see part of it is starting to regain its dark green color, i.e., it is beginning to heal. Equally important, this healed healthy patch of phloem is just beginning to radiate the propiconazole fungicide inward! So, once the phloem layer is healed, the internal white canker fungus gets attacked from two sides. We'll see more of this in later photos.

Photo 10 - Day 7 - andromeda twig cross-section		Photo 11 - Day 7 - andromeda leaf cross-section		Photo 12 - Day 7 - andromeda leaf cross-section		Photo 13 - Day 7 - andromeda leaf cross-section

While all these changes are taking place inside the twig, it's also instructive to see what effect the fungicide is having inside the leaf. Photo 14 (top) shows a cross-section of the left half of a leaf (the midrib is on the right, and the leaf surface is facing up), while photo 15 (bottom) shows a cross-section of the right half of this leaf (midrib on the left, and the leaf surface is facing up).

Recall the white canker fungus is always white, regardless of the part of the plant it is in. Instead, here it is black! The reason is that the fungicide has killed it, and dead white canker is black. As you can see, there were numerous patches of white canker in the interior of this leaf. As before, click the photo to see more detail.

Photos 14 & 15 - Day 9 - andromeda leaf cross-section

Leaf junctions are especially fascinating to study. The reason is that white canker fruiting bodies and their supporting fungal hypha tend to grow densely there. Hence, when making a twig cross-section, I often gravitate toward making my cut at a leaf or branch junction. Photos 16, 17, and 18 were taken on successive days and show these junctions. Once again, the brown coloring indicates white canker that is dying due to the fungicide treatment.

Photo 16 - day 9 - Andromeda twig cross-section		Photo 17 - day 10 - Andromeda twig cross-section		Photo 18 - day 11 - Andromeda twig cross-section

Not a lot of change on this day. Photo 19 shows the cross-section of a small, new twig. Again, the brown coloring indicates the death of white canker taking place. Also visible is part of the twig surface on the upper-left, where you can see some of the whtie fruiting bodies. If a fruiting body has already developed, the fungicide doesn't seem to kill it. Photo 20 shows a badly infected larger twig. Its center pith is definitely not a healthy frothy white, and the xylem adjacent to it has a lot of white in it. But of most importance is the bad shape of the phloem. It has become so infiltrated and shrunken that it has actually pulled away from the adjacent xylem, leaving a gap between them.

Photo 19 - Day 14 - Andromeda twig cross-section		Photo 20 - Day 14 - Andromeda twig cross-section

On day 16 you can see a significant change taking place. Photo 19 shows a small, new twig. Note the difference in texture between the green phloem in the upper part of the twig and the lower part. The white canker has been eliminated from the upper part and replaced by rich, deep green tissue. In fact, it has a "wet" appearance. In contrast, the lower phloem is still infiltrated with dying brown white canker blobs.

Photo 20 shows a larger twig which is older. The bark is still infiltrated with white canker and the pith is still badly infected. But the phloem is regaining its nice healthy green color. Because the phloem is now much healthier, it can more easily do its normal transport job, and is now transporting fungicide inward toward the pith. Note the "green wave" moving inward, eliminating the white canker rays that used to radiate out from the pith. This twig is well along on its way to health!

Photo 21 - Day 16 - Andromeda twig cross-section		Photo 22 - Day 16 - Andromeda twig cross-section

At this point in time, it is becoming apparent that there is a difference in the rate of recovery of different twigs. At first, there doesn't seem to be any pattern, but as more twigs are sampled, there seems to be a general pattern emerging. It appears that newer growth is showing the fastest rate of recovery, while older, established growth is recovering very slowly. Fortunately for documentation purposes here, the age of a twig can easily be determined by the amount of bark it has: a new twig will have no bark and an older twig will have increasing amounts of bark.

Photos 23 and 24 illustrate this. Photo 23 shows a relatively new twig. Look at it closely and you may notice that a major battle is taking place within it. The phloem is a reasonably healthy green. While the newly forming bark tissue outside of it is riddled with canker, much of this canker is yellowish in color, meaning it is dying and being replaced with healthy green tissue. This is especially true at the top, just to the left of the leaf junction. The white canker there is virtually gone, and only a few diffuse yellow blobs of dying canker remain. Furthermore, this healthy new growth is infusing the xylem under it, killing the white canker there and turning the white-green coloring to a more normal greenish color.

In contrast, photo 24 is an older twig, since it has bark. But this twig isn't doing quite as well. The phloem at the sides isn't too bad, but the phloem at the top has degraded so much that it has separated from the xylem. The healthiest phloem is at the very bottom of the photo, where it appears almost "wet". Inside the phloem, things are much worse. Specifically, the pith isn't frothy white. Its yellow color means that the white canker hypha infiltrating it is still dying off. Outside that, the xylem still contains lots of infiltrating white canker.

Photo 23 - Day 18 - Andromeda twig cross-section		Photo 24 - Day 18 - Andromeda twig cross-section

Photo 25 shows progress in the twig healing process of a new twig. Specifically, the pith has lost almost all of its yellow color. The newly forming bark tissue outside of the phloem seems to contain less and less white canker, and it also has more of that healthy "juicy" look (top and lower left). The way this twig was mounted shows a bit of the outside bark in the lower right side of the photo. Some of the white canker there has died and turned black. But the air gaps between the phloem and xylem means that much more healing will have to take place.

In contrast, photo 26 is of an older twig that is still in bad shape. The bark is distorted and filled with white canker. the normally green phloem is almost dead, and has separated from the xylem on the right. Moving inward, the xylem still contains lots of white canker. Finally, the pith is yellow, meaning the white canker is dying there. In summary, this twig has a long way to go before it is healthy.

Photo 25 - Day 21 - Andromeda twig cross-section		Photo 26 - Day 21 - Andromeda twig cross-section

Photo 27 shows a new twig with a cross-section made just at the base of a leaf (left side of photo). This is usually the location where white canker concentrates, and while its density is apparent here, you can also see that it is dying off. The green phloem, which was badly infiltrated with white canker, now is infiltrated by dead or dying white canker, and some of this canker is being replaced by healthy green tissue. Also, the pith is starting to regain some of its white frothy appearance.

In contrast, photo 25 shows an older twig which still has a long way to go to regain its health: the pith is still yellow, the xylem has lots of white canker "rays", the phloem is almost totally degraded and is also separated from its xylem.

Photo 27 - Day 25 - Andromeda twig cross-section		Photo 28 - Day 25 - Andromeda twig cross-section

Photo 29 shows a badly infected young twig. Once again, this cross-section was taken just at the point where a leaf was branching off, since that's where white canker concentrates. And, as you might expect, that also happens to be the location where major white canker death is also taking place. In certain parts there, the white canker was so dense that all the tissue died, leaving a black void. And in one of these large voids, the white canker grew fruiting bodies within this void! Apparently the genetic code of white canker said "if there is no live tissue around you, grow fruiting bodies"! Another mass of these fruiting bodies can be seen on the twig surface at the lower-right part of the photo.

Photo 29 - Day 27 - Andromeda twig cross-section		Photo 30 - Day 29 - Andromeda twig cross-section		Photo 31 - Day 29 - Andromeda twig cross-section

Photo 30 shows a young twig well along in the healing process. The white frothy pith is returning, and while there are some gaps in the phloem-xylem junction, the phloem seems to be closing the gap with new tissue! In particular, check out the lower-left phloem - the white canker has been almost totally dissolved and replaced by healthy green tissue (again, with a wet appearance).

Photo 31 is the first twig sample having bark that shows mostly healthy green xylem! Unfortunately, the white canker so severely damaged this twig that there are huge voids between the xylem and phloem, so this twig has a long way to go before it is completely healed.

Photo 32 shows a vigorous attack on a white canker infection by the fungicide. For reference, check out the lower-right phloem and surface tissue, which shows dead phloem and badly infiltrated surface tissue (with a few fruiting bodies on its surface). Now compare this to the lower-left phloem and surface. The difference amazing - the xylem-phloem junction is smooth and sharp, and the twig surface is smooth and round, with no white canker in it, and no white canker fruiting bodies on the surface.

But, as you move upward, the phloem was so infiltrated with white canker that the fungicide totally killed it off, leaving a black area where the phloem used to be. Since there is no healthy phloem there, it couldn't kill the white canker growing on the newly forming bark. Likewise, the white canker was protected from destruction by the dead/weakened phloem on the upper and right side of the photo. And, as seen before, note the white canker fruiting bodies growing in a dead section of tissue (right of photo). And note the abundance of fruiting bodies on the twig surface at the upper-right.

What's new that is being demonstrated in the set of photos taken at this time period is the fact that once the fungicide gets the phloem sufficiently healed, the phloem then radiates the fungicide both inward and outward. This greatly accelerates the healing process. Photo 33 dramatically illustrates this. At this point in time, much of the phloem has healed, and it is radiating healing both inward and outward, wiping out the white canker in the process. To fully appreciate this, check out the areas where the phloem is pretty much dead (brown) - the new bark area there is still riddled with white canker. And that area on the right will have to heal the void before the bark area behind it can be healed.

Photo 32 - Day 31 - Andromeda twig cross-section		Photo 33 - Day 36 - Andromeda twig cross-section		Photo 34 - Day 37 - Andromeda twig cross-section

Photo 34 shows another twig in the healing process. Like we've seen in prior photos, not all internal parts heal equally. Here the lower-left has begun the healing process first, once again generating a very smooth looking surface with no white canker present in the new bark or phloem underneath it. And once again, the infected areas contain white canker both internally and on the surface in the form of fruiting bodies. Apparently, when the healing process kills the internal white canker, it also causes the white canker fruiting bodies to be shed.

While the fungicide is working to destroy white canker on the internal tissue of the twig, it is also working to destroy white canker on the surface of the twig. This surface white canker consists mostly of these off-white colored globular fruiting bodies along with their supporting fungal tissue.

As many other photos of white canker on leaf surfaces have shown, white canker fruiting bodies tend to congregate around a relatively abundant food source - the leaf veins. Photos 35, 36, and 37 illustrate this clustering. Except for the whitish fruiting bodies, all other supporting white canker tissue has been killed. Other photos show that these fruiting bodies are attached to plant tissue by a very small stalk. Apparently, when this stalk is killed, it is greatly weakened, and the fruiting body is then shed, which is probably why we don't see any dead fruiting bodies.

Photo 35 - Day 39 - Andromeda leaf surface 1		Photo 36 - Day 39 - Andromeda leaf surface 2		Photo 37 - Day 39 - Andromeda leaf surface 3

At this point in time, we may be seeing the peak of healing for andromeda twigs having some bark, as photo 38 shows. Here the phloem seems to sparkle a bit with health, and has no embedded white canker. While there is a significant void on the right, zooming in to the area just above that void will show that it is very wet due to the bush trying to heal that void. The bark is also relatively free of white canker.

Photo 39 shows another young twig that appears to be well on its way to healing. The entire lower left phloem and new bark seems to pretty much canker free, and the rest of the phloem has a lot of brown in it, indicating dying canker. On the other hand, the xylem is more white than it probably should be, and the center pith is only partly frothy.

Photo 38 - Day 39 - Andromeda twig cross-section		Photo 39 - Day 41 - Andromeda twig cross-section		Photo 40 - Day 45 - Andromeda twig cross-section

Photo 40 shows a young twig where the cross-section cut was made slightly above the point where the leaf jointed its supporting twig. This particular cut enables us to see the inside surface of the twig-leaf junction, and area where white canker fruiting bodies normally congregate. And that's the case here, where you can see a number of these white fruiting bodies. Of interest, however, are the numerous small black dots scattered there. These are most likely the fungal attachment points of former fruiting bodies.

Looking at the supporting twig cross-section, we can see lots of brown tissue external to the pith, indicating that the fungicide is still locked in a battle with the white canker. But, this being a young twig, I would have expected more progress in clearing the white canker. Again, there is the distinct possibility that the fungicide has reached its peak effectiveness, with white canker beginning to increase.

At first glance, photo 41 has an overall green tinge, so looks healthy. On the other hand, there is very little brown coloration within the white canker outside of the phloem. The phloem also doesn't have a deep green healthy appearance. And the xylem is also getting more white in color. The evidence seems strong that the fungicide has lost its effectiveness. (Due to a scanning error, only about half of this twig is shown.)

The twig with bark shown in photo 42 somewhat supports this conclusion. The phloem is fairly well-formed and shows signs of healing. However, this healing is not progressing inward, as it should do when the phloem is healthy. Instead, the xylem is white with canker. Also, the center pith is a brownish-orange, and not at all close to frothy white.

Photo 41 - Day 49 - Andromeda twig cross-section		Photo 42 - Day 49 - Andromeda twig cross-section

As discussed earlier on, it's unfortunate, but every twig sample shown here means we can never look at that twig again. And while this test andromeda bush has lots of twigs available for sampling, different twigs respond a bit differently to the fungicide. Consequently, we have to look for general trends instead of basing a conclusion on one or two sampled twigs.

Like photo 41, photo 43, taken 4 days later, also shows a twig containing a lot of white canker, with very little of it brown in color. The lower phloem is nice an green, so we know the fungicide worked. But it doesn't seem to be working any more.

Photo 44 shows a twig with bark 20 days later. While the cracked bark and big voids show that this twig was in terrible shape due to white canker, the xylem is pretty much a healthy green color. And the phloem at the bottom seems to be healing by again joining with the adjacent xylem.

Of particular interest here is that my tree and shrub care company sprayed our yard with the fungicide propiconazole on July 28, which was 12 days before photo 44 was taken. That is a good amount of time for the effect of a fungicide to be seen. Sure enough, when you click on photo 44 and examine it closely (especially the top and top-right), you'll see a fairly well defined ring in the xylem around the center pith. Inside this ring, the xylem is a bit more yellow in color (dying canker). This inner area also contains less white canker. Assuming this ring continues to radiate outward at the same rate, it would cover the entire xylem in about 24 more days. At that point it would probably infuse the adjacent phloem and help to heal it. If we assume that, too, would take about 12 days, then the full effect of the fungicide treatment would be complete in about 48 days, or about 7 weeks.

Photo 43 - Day 53 - Andromeda twig cross-section		Photo 44 - Day 73 - Andromeda twig cross-section

At this point in time, this test andromeda bush has had 3 treatments of the fungicide propiconazole: 83 days ago, 22 days ago, and about 6 days ago. The first two were by a commercial tree and shrub care company (foliage spray), and the last was by me (ground spray).

Photo 45 shows a cross-section of a new twig, and was taken about 8" from a branch tip. Again, in order to get a better picture of what was going on, I made the cross-section cut so that it also included a leaf stem cut (right side of photo). As has been seen previously, there is a healing halo around the pith and within the xylem. The outer part of the halo is yellow, while the inside is greener, meaning that the white canker density is decreased as this fungicide healing wave moves outward. The pith is white, but still isn't the nice soap-bubble frothy white. But the phloem is mostly a nice rich green, and has a well-defined edge. The surface between the twig and leaf stem is clear of all white canker fruiting bodies, with only a few remaining dead black spots. Unfortunately, the newly forming bark outside the phloem still contains a fair amount of white canker, especially in the upper-left, which is the base of another leaf.

Photo 46 was taken a few inches inward from where the cross-section shown in photo 45 was taken. Once again, the older twigs, such as this one, are relatively slow to heal. In particular, the pith is yellow, the xylem is still pretty infused with white canker, the phloem is thin and generally unhealthy , and the bark looks pretty bad. The only good news here is in the lower-right area of the photo where healthy phloem is beginning to infuse into the adjacent xylem and totally clear it of white canker. It appears that healthy phloem tissue is of major importance in clearing a white canker infection.

Photo 45 - Day 83 - Andromeda twig cross-section		Photo 46 - Day 83 - Andromeda twig cross-section

No doubt you've noticed many gaps in the preceding period of sampling. I had made many more cross-sections, but the ones I left out were very similar to those shown above, so offered no new information.

A review of all the twig cross-sections shown above yields the following set of conclusions:

• The white canker infection pattern of the andromeda bush is similar to that in other trees and bushes
• White canker is present in all plant tissue
• Healthy phloem tissue will appear dark green and "juicy" in a twig cross-section
• Even internally, white canker growth tends to congregate between a twig and its leaf stem

• The plant interior and its health will begin to improve after 3 or 4 days
• Significant interior healing will take place in about 10 days
• The fungicide treatment is good for about 7 weeks - after that, white canker slowly returns
• Multiple periodic applications are required to control white canker
• New growth benefits from a fungicide treatment far more than older growth

• Slowly dying white canker is brown in color
• Surface white canker killed by fungicide propiconazole will turn coal black
• Interior heavily infected white canker killed by fungicide propiconazole will also turn black
• Fungicide killing action proceeds both outward from the outer pith, and inward from the phloem
• Fungicide kills the fruiting body's support structure, causing the fruiting bodies to fall off

• Fungicide propiconazole will kill white canker, not just inhibit its growth
• Killed white canker in the xylem and phloem is replaced initially by dark green tissue
• To heal the bark, the phloem must be in contact with it