Black Spot (Roses) Description: Primarily affects roses. At first, lower leaves of susceptible plants become covered with brownish black spots; eventually they 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. Solution: Avoid wetting foliage. Prune plant to allow good air circulation among branches. At the first sign of disease, remove infected leaves and begin using Soap-Shieldฎ Fungicidal Soap, Liquid Sulfur or Micronized Sulfur on a regular basis for control. Clean up any dead leaves from the base of plants (don’t compost dead or diseased leaves), especially in fall.