Question From: Alamosa, Colorado, United States
Q: I have a white powder on my crab apple tree where the branches have been trimmed in the past and it has spread to our neighbors tree also. It is spreading rapidly.
A: The white powder is powdery mildew. Here's a link to information about the disease and control: http://extension.psu.edu/plants/tree-fruit/diseases/apple-diseases/powdery-mildew . Best And Happy Yardening, Nancy
