Diseases in Trees: How Much Can Trees Tolerate?
As summer wears on, we see more and more damage from diseases accumulating on landscape trees. How much is too much? It depends on the tree, the diseases that it has, the time of season. Although we do not have frequent disease problems in trees in Montana, there are many diseases that can attack trees, and they can be difficult to diagnose. Some common symptoms that can probably be ignored are the powdery, white accumulations on foliage caused by powdery mildew; the small, round spots of orange powder caused by rust fungi, usually found on the undersides of leaves and causing a corresponding yellow or pale spot on top of the leaf. Sooty mold, which is a fungus that forms in association with aphids is usually not a serious problem either. Most of the pathogens that cause brown or black spots on tree leaves are not serious; if the levels are very high, they can sometimes cause twig dieback. In those instances, prune and dispose of the heavily infected branches. Generally speaking, by Se
