Q: We have a number of magnolia trees in our yard. On some of them the leaves are heavily infested with circular brown spots, about a quarter of an inch in diameter. Any thoughts?
A: It’s probably algal leaf spot. Holly Thornton, University of Georgia plant pathologist says this leaf disease usually follows rainy, wet weather in the fall or spring. Management can be achieved primarily by sanitation. Remove infected attached and fallen leaves and destroy them. Increasing air circulation around the trees and improving soil drainage will help prevent future infections. Copper sprays, such as Kocide 101 (click for sources), can be used preventively but are usually unnecessary.