Cercospora leaf spot caused by Cercospora violae, can damage the overall appearance of pansies and reduce their marketability and value. The disease is favored by extended periods of high humidity with nighttime leaf-wetting and daytime drying. The disease can come in through infected seed or weeds of the Viola family. The fungus overwinters in seed, infected crop residues, or in weeds of viola family. A few infected plants can produce large amounts of inoculum causing a lot of plants in the house to be infected. Small black, circular spots form on the lower leaves under moist conditions. Remove severely spotted plants or leaves and avoid overhead watering late in the date so that foliage does not remain wet for prolonged periods. Remove weeds and crop debris that may harbor the disease. Apply a fungicide registered for use on pansies such as thiophanate methyl & chlorothalonil (Spectro 90 WDG), chlorothalonil (Daconil Weather Stik), triadimefon (Strike 50WDG) or Bacillus subtilis QST713 (Cease)
Geoffrey Njue, UMass Extension
