The antibiotic streptomycin is used in commercial agriculture, but is not available to the homeowner. Leaf spots are characterized by brown or black spots randomly scattered across the leaf. The spots may or may not have the appearance of concentric rings. The margins of the spot may be a different color than the center of the spot. Leaf spots are caused by many different fungi that attack landscape ornamentals.
Rainy periods favor their sporulation and spread to unaffected foliage.
Infection may occur at any time, but the disease is usually most severe on new, emerging foliage during rainy periods. The new spring infections are commonly caused by spores from last fall's leaves. Therefore, rake and burn or compost last season's leaves before buds break in the spring. Help foliage dry quickly after rain, heavy dew, or sprinkler watering. In the case of deciduous trees and shrubs, prune out overthick growth for better penetration of solar radiation and better air circulation to aid in drying foliage.