In the southeastern USA, bedding plant production and landscape installation in the fall is dominated by pansies and violas. Plant diseases can greatly affect the quality and longevity of these beautiful bedding plants. Pansies and violas are affected by numerous plant diseases including black root rot, Pythium root rot, powdery mildew, Botrytis blight, and Cercospora leaf spot. During the winter and spring of 2020, there was also a major problem with Myrothecium crown rot. Pansy is also affected by downy mildew. However, the disease occurs sporadically.
The most common leaf spot disease on pansy is Cercospora leaf spot, caused by the fungus, Cercospora violae. Symptoms of Cercospora leaf spot begin as small, purplish spots with a fringed margin. Leaf spots enlarge and may develop a tan center. Cercospora spores are produced within the center of each spot and may be seen on their sporebearing stalks with a hand lens. Prolonged periods of leaf wetness, high humidity, poor air circulation, and moderately cool temperatures favor infection and disease development.
Cercospora leaf spot is a constant problem in both pansy production and landscape installations. The fungal pathogen is specific to pansy and viola. Contaminated seed and infected plant debris may be sources of initial infection. Once present, the spores are easily spread by watersplash, air currents, and worker activity touching wet plants. Within plug trays, the disease can spread quickly and even kill plants. Remove severely infected plants to reduce disease spread. All plant debris should be discarded or destroyed at the end of the production cycle to reduce pathogen survival. Reducing leaf wetness periods by changing irrigation pattern, timing, and type so that plant foliage will dry quickly can reduce disease development. Spray applications of fungicides containing azoxystrobin, chlorothalonil, copper hydroxide, mancozeb, myclobutanil, potassium bicarbonate, propiconazole, pyraclostrobin, tebuconazole, trifloxystrobin, and triflumizole can reduce Cercospora leaf spot infection.
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