I receive a lot of questions this time of year about plant fungal diseases. That's because our rainy season is about over and folks have begun using their irrigation systems in earnest. Usually, these questions center around roses, but fungal diseases occur on a variety of plants. This time of year, they most commonly appear on roses and rose-related plants like photinias, fruit trees and pyracantha. Non-rose family trees and shrubs to commonly get fungal diseases are magnolia, holly and viburnum.
Many gardeners discover black or brown spots on the plant's leaves.
Although this is a specific pathogen to the Rose Family, the term and its identification can be equally applied to other trees and shrubs, as well. In coastal areas like the Pacific Northwest and southeast Atlantic states, Rose Rust is also common. This disease appears as tiny rust-colored dots and splotches along stems and the underside of leaves. And reports of Downy Mildew along the Gulf Coast have indicated this fungal pest may be destroying many gardens. Downy Mildew appears similar to blackspot, but infected leaves develop irregular purplish-red spots.