Question: Our cedar elm turns rusty brown in the summer each year. Why?
Answer: If you look closely at the backs of the leaves when you first see this happen you’ll normally see a dusting of powdery mildew fungus. The bottoms of the leaves will take on almost a silvery appearance. Next step: the russeting of the tops of the leaves. To control the problem, apply a fungicide labeled for powdery mildew. The problem isn’t life-threatening, however, and you may decide it’s too much trouble to try to spray for it, especially if your cedar elm has grown to any size. It’s primarily cosmetic.