We are in Bracebridge. A large maple approximately 14 diameter at the base and 60 ft high is starting to drop some leaves. The ones down have a black spot on them. When I look up into the tree can see black spot on some of those as well. Any idea what it could be – what we should do? It is otherwise a healthy and growing with full foliage.
Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) has posted a notice about the high incidence of leaf spot and leaf blight on several native species of maple this year. They explain that unusually cold spring, which prolonged leaf emergence, and the near constant wet conditions were perfect for supporting several fungal and bacterial diseases.
However, they also explain that these symptoms do NOT require any treatment, as the new leaves now emerging will be fine.
For full details and images, visit the OMAFRA blog here.