Hello, we met some of your folks at the CNE and they recommended we email you our question. We have a red maple in our back yard and this year it has a white powdery looking fungus on it. You can see what it looks like from the picture attached. Is this something we need to treat or will it go away when the leaves fall and if we rack them up well it shouldt appear next year?
The leaves of your red maple tree appear to be infected with powdery mildew. Powdery mildew is a common fungal disease characterized by a white, powdery coating on leaves and petioles (leaf stems). The leaves may turn yellow, drop early, or become twisted. The white patches may also develop black spots as the fungus prepares to overwinter. Powdery mildew arises late in the season during warm, humid weather and cool nights. Although the mildew is unsightly, the damage caused by the disease to the maple tree is minimal.
The powdery mildew fungus overwinters in leaf debris, and to manage the disease be sure to gather up and remove from the property all fallen leaves in autumn. Fungicides purchased from your local garden center can be applied during the growing season as soon as you notice white patches on the maple leaves. Once the fungus has been spoted during the growing season avoid applying nitrogen fertilizers to the tree. Nitrogen increases the production of foliage and provides more material for the fungus. Avoid late evening and overhead watering, this will help reduce the dampness and humidity.