Hello, I have a dwarf red Japanese Maple tree that is losing beginning to bare leaves and those that remain have a white powdery substance on them. I've been told it is a type of fungus or mildew. Three questions - What may have caused this to happen? - How do I treat it? - How do I prevent it? The plant is on the west side of the building in a 36" bed that is covered with pine needles. We have had an incredibly hot summer in NC (2018) and then significant rain (five to eight inches) in a short period of time. This area does catch all of the overflow from the downspouts when the storm sewer cannot handle the volume of water. This maple was planted in 2012 but I'm not sure of the age at the time of planting
I think it is powdery mildew. It tends here (in my landscape) in August when we have overnight fogs. IIRC, you've recently had a lot of rain in the area and probably continue to have very high humidity. It isn't a serious worry because the leaves will be dropping soon anyway.
Yes, powdery mildew. Likes to happen when there's either too much or too little moisture. Not dangerous for the maple, so just clean up the leaves. If you want you can use a foliar fungicide next year, or a copper-based spray like phyton27. Try and avoid systemic fungicides with maples. But remember: once you see it, it's too late (though not really harmful). So if you have difficult conditions again, you may want to spray prophylactically.
