The Q&A Archives: strange new growth on oaks

Question: Happy spring! In Nov. we had our two oaks (we live in Woodland hills and I think they are coastal oaks?, the ones that constently lose and grow new leaves), and when the new growth came in, it was covered in white powder, and looking stunted and like powdery mildew covering all the new leaves and new wood. Any ideas? should I be alarmed? Maybe I had the trees trimmed at the wrong time? The other oaks in the neighborhood don't have this . I appreciate you guys being there and any advise will be greatly appreciated! Tanks so much, nanc

Answer: What you describe does sound like powdery mildew. Oaks are more susceptible to this disease while new shoots are developing and leaves expanding; mature leaves become more resistant. Unfortunately, cultural practices, such as trimming, and fertilizing that stimulate and prolong succulent plant growth encourage powdery mildew.

Powdery mildew may be treated with commercially produced fungicides. These products may include sulfur, fenarimol, dinocap, triadimifon or benomyl. Refer to the instructions on the package to determine method and timing of application. Weather conditions such as temperature and humidity are important factors when determining when to apply fungicides.

Hope your oaks regain their health!

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