Our beautiful red maples are dropping dead

[Don Peters]

Here in New England, one of the most beautiful times of the year is in the fall, when the leaves turn color. And many would say that the most colorful trees in the fall are the red maples, which often turn a bright red. But these maples have been declining the past few years. There was one in our housing development which my wife and I agree is the best of the best - it turns a bright crimson red in the fall. We check it out every year. It has always seemed to resist attack by white canker. But last year I noticed the leaves sagging a bit more than usual. I was hoping it was just my imagination. Unfortunately, this summer there are a lot of its leaves dropping. Numerous branches within the canopy are dead. But, true, we are having a very warm and dry summer.

But other red maples are also showing signs of severe stress. In fact, one of my neighbors has one, and within a week every single leaf on it died! I had been following this tree. Several years ago a windstorm broke the top off, and soonafter it seemed to acquire some symptoms of white canker. (I assume the white canker spores got in through the large wound.) But I never expected such a sudden dieoff. Here's a picture of the tree:

Of course, by simply looking at this tree you don't get much insight as to why it died. So I broke off a small 1/8" (3mm) diameter twig, cut it with a razor, and then looked down into its cross-section with a 400x digital microscope. I took 20 pictures all around the periphery of the twig, and then used Microsoft's ICE picture stitching software to combine them all into one picture, which I include here:

(The inner white xylem is not shown since its not diagnostic.) As you can see, there is only a trace of the green phloem left under the bark (lower-left). Almost all the phloem has been infiltrated by a white fungus, so the normally green phloem is now more white than green. You can see the fungus almost oozing out from under the bark on the left side (hair-like translucent strands). The right half of this twig has started to die, and is turning black.

I suspect the reason this tree died suddenly was that it was just barely hanging on because its nutrient carrying system in the phloem was almost totally clogged with fungus. The recent heatwave combined with a relative lack of water simply pushed it over the edge.

Will it come back? Often times when a tree is hit with a massive defoliation, as with insects, it will refoliate within weeks, although this takes a severe toll on the tree's energy supply. In fact, the branch I sampled does have very small green leaf buds. But the severe damage to the green phloem argues for no comeback, or a very weak comeback. Meanwhile, will the homeowners give up on the tree and cut it down? Stay tuned...  (this is the third week in July - the hottest time of the year)

[Don Peters]

I saw another red maple that looked in sad shape, and decided to take a much closer look at it. Here it is:

Although there is only a dead branch or two, as you can see, the foliage is very sparse, and many leaves have already fallen. Curiously, the right side of this tree is mainly south-facing, so gets most of the sun. Apparently the sun's energy is helping keep this tree going.

Except for the leaves drooping and being rather small, I saw no canker on the top or bottom surface of them.

But the bark was another matter. Actually, as is typical, most of the bark is clean. However, there were extensive patches of spores at the underside of branch junctions, as shown in the following branch surface microscope photo taken at 400x:

Once again, the white spores are about 50 microns in diameter and the smaller yellow spheres are about half that size.

If white canker is really present, some of the best evidence is a detailed view of the cross-section of a twig or small branch. This time I took a quarter-inch diameter branch as a sample. Using my digital microscope, I then carefully took about 60 overlapping photos at 400x around the edge of the cross-section so I could capture all of the area just under the bark. I then used Microsoft's ICE photo stitching program to compose one large image. A small view of it follows:



This photo shows of how badly this tree is diseased. Only a trace of the normally green phloem is present, having been replaced by white canker material. The bark is separating from the phloem, as if it is trying to get away from it. Only a very thin layer of phloem remains immediately under the bark, and even there it only extends about half-way around. I've also made the full-resolution photo available on this website - check it out by zooming into it, at: www.whitecanker.net/pictures/2010-07-24 Maple branch cross-section donut.jpg
(Right click the picture to save it to your PC or to print it.) As you zoom-in to examine the details, you'll gain a better appreciation of how devastating this disease is to the inner part of the tree. The chaos there reminds one of a war going on. And, in fact, there is.

You'll note that these photos don't include the central xylem, which is usually a boring white. You can see the edge of it in the above photos. However, white canker does infect this xylem. Apparently it has killed part of the xylem in the center of this branch, as the following stitched photomicrograph shows:
The reason I suspect white canker killed this tissue is that there appears to be white canker within and around this black tissue. Not only that, but to the lower-left of this dead area is a patch of white canker blobs. Apparently, when the white canker density gets high enough, it kills off the white xylem tissue. Furthermore, as the snow-white xylem begins to die, it seems to turn brown, further highlighting the infiltration of white canker blobs.