Primarily affects roses. At first, lower leaves of susceptible plants become covered with brownish-black spots; eventually the leaves yellow and drop off. A severe infestation can completely defoliate a plant over a period of weeks. Disease spores are spread by rain and irrigation. Black spot spreads quickly in wet or humid, warm weather.
Avoid wetting foliage. Prune plants to allow good air circulation among branches. At the first sign of disease, remove infected leaves and begin spraying a sulfur-based fungicide or a soil inoculant every 5-7 days for control. Clean up any dead leaves from the base of plants (don't compost dead or diseased leaves), especially in fall. We recommend Plant Guardian™ Biofungicide Liquid Concentrate or Rose & Ornamental Plant Spray.