Have you noticed lots of leaves falling from your ash trees this past week (week of May 17th)? Do the leaves look like this?
These trees will recover within the next couple of weeks, and will look fine for the rest of the season, with no permanent harm. The culprit is a fungus disease called ash anthracnose, and the reason it is so noticeable this year is because we had a week of rainy weather just as the leaves were in their most vulnerable stage -partially expanded. Once the leaves are fully formed, they will no longer be susceptible to the ash anthracnose pathogen, even if the spores are present and climatic conditions favor the disease. Don’t let anyone talk you into treating this disease – sprays, injections or any other treatments will do absolutely no good. In order to effectively treat this disease, the fungicide must be applied BEFORE the symptoms reach this point. Because we can’t predict the weather in any given year, to treat a tree for ash anthracnose involves a fungicide application PREVENTIVELY, whether it will make a difference (wet spring) or not (dry weather at leaf expansion time). Ash anthracnose poses very little impact on the health of a healthy ash tree. It is mostly a nuisance (and perhaps a surprise) to the tree owner. I do not recommend bothering with preventive sprays, unless the tree is already in precarious health or the tree is located where the leaf-drop nuisance is actually a real problem.