How to Identify Blight Cankers
On smooth-barked young trees, such as shown below at left and center, cankers typically are orange in colr,in comparison with the gun-metal gray to green color of the uncankered stem. This orange color is especially evident when the bark is wet. Cankers typically will also bear numerous orange fruiting pustules, or stromata, of the blight fungus. The orange color of individual stromata is not clearly depicted in the rough photographs below, but is easily visible to the naked eye in nature. Most of the orange color in the left-hand photograph is due to stromata, and most of the pimply-looking bumps on the canker in the center photograph are stromata.
On older, rough-barked trees, like that in the right-hand photograph, most of the canker will be hidden underneath the bark. Frequently, the only sign of the canker will be orange-colored longitudinal cracks in the bark, as at the arrows. Close examination fof those cracks frequently will reveal rows of orange stromata buried within. A flashlight can facilitate observation of the buried stromata.
Soil Compresses for Curing Individual Chestnut Blight Cankers
By Dr. Fred Hebard
The chestnut blight fungus usually cannot attack the roots of chestnut trees, because other microorganisms in the soil attack the blight fungus. One can take advantage of this phenomenon and cure individual blight cankers by moving soil up onto the trunk of chestnut trees. You do this by placing a soil compress (or mud pack) over the canker.
The blight fungus attacks chestnut trees by forming cankers on their stem. A canker is a region of dead bark on a tree. Chestnut trees are killed by blight when a canker completely encircles the stem, cutting off the flow of water up from the roots to the leaves and the flow of sugar down from the leaves to the roots. Trees can have multiple cankers, and each one is capable of encircling the stem. To protect trees from blight using soil compresses, it is necessary to treat each canker on the tree. Furthermore, continued vigilance is necessary to detect and treat new cankers on the tree. In general, soil compresses offer a means of prolonging the life of chestnut trees; they are not a general cure for the disease. As trees increase in size, it becomes increasingly difficult to treat all the cankers on the tree, especially higher in the tree, and it also becomes more difficult to detect cankers that need to be treated.
For a soil compress to work, the soil must be held in place over the entire canker and kept moist. You can do this by covering the compress with shrink wrap, sold at building supply stores. The 4″ rolls are easiest to handle.
The other important requirement is to have the compress extend at least 1 foot beyond the top and bottom edges of the canker, so that the canker doesn’t expand beyond the edge of the compress before the soil microorganisms have a chance to attack the blight fungus.
The easiest way to apply a compress is to make gooey mud from soil around 10 feet from the tree and stick it to the cankered area, completely encircling the stem. Sometimes you can stick the mud to the tree by forcefully throwing handfuls at the stem. Be sure to completely cover the stem. Then wrap the mud firmly with the shrink wrap and completely seal.
Every month, check the top and bottom edges of the compress to make sure the canker has not expanded beyond the edges. Remove and reapply the compress after 1 year.