The wet, blistering hot weather that we all suffered through this Memorial Day weekend has hurt the Maples this spring. Several foliar diseases have developed which cause black spots on leaves and leaf fall. Anthracnose and Maple Leaf Blister are the most common causes and usually do not warrant control. The weather has changed to cooler, drier conditions and these cosmetic diseases should be arrested as the season progresses.
Although startling, I seldom recommend fungicide treatments unless the trees are in prime landscape locations or are important or sentimental to a client.
I have seen a much more rare disease in Dane and the west side of Madison. Bacterial Leaf Scorch affects the entire crown of the tree at once as it is a Vascular Bacteria rather than a Foliar Fungus. This disease re-occurs year after year until successive defoliation weaken the tree and eventually the trees die back. This disease can be controlled with injections of Antibiotics.