IDENTIFICATION — In spring small black spots appear on the leaves, and occasionally the stems, of roses. The spots look like soot, but can’t be rubbed off.
DAMAGE — By summer the spots grow larger, the leaves turn yellow, fall off and are replaced by new leaves. Repeating this process weakens the plant, making it more susceptible to other diseases, insects and winter injury. Plus, it’s just plain unsightly.
Fungus spores overwinter on infected leaves and stems left lying on the ground. Splashing water transfers the fungus to young leaves from spring through fall.
CONTROL — Search out resistant cultivars and grow roses where air is not blocked by surrounding plants. Avoid wetting the leaves, especially late in the day, and remove infected leaves as you spot them. Fungicides from the garden center will help, but spray before you see symptoms.