Suppression of gummy stem blight on watermelon and cantaloupe transplants with seed-applied fungicides

• Published in: Phytopathology Vol. 94; no. 6
• Main Author: Seebold, K W
• Format: Journal Article
• Language: English
• Published: 01.06.2004
• Subjects: Citrullus lanatus; Cucumis melo cantalupensis; Didymella bryoniae
• ISSN: 0031-949X

Gummy stem blight (GSB), caused by Didymella bryoniae, is the most destructive disease of watermelon and cantaloupe in the southeastern U.S. Epidemics of GSB in transplant production houses have become severe in recent years. Inoculum may be seedborne, or can enter transplant houses from external sources. Boscalid and tebuconazole were applied to untreated seed of watermelon (diploid and triploid) and cantaloupe at rates of 25 and 2.5 g of active ingredient per 100 kg of seed, respectively, to determine effects on the development of GSB on transplants. Seedlings were inoculated with a mycelial suspension of D. bryoniae (50,000 CFU per ml) at the appearance of the first true leaf; trays were covered with a plastic-tarped frame to maintain high humidity. At 2 weeks after inoculation, boscalid reduced the severity of GSB on inoculated plants by 60% and secondary spread was reduced by 80% compared to the untreated control. Tebuconazole did not affect GSB on inoculated plants; however, secondary spread was cut by 27%. Seed treatment may be an effective way to manage outbreaks of GSB on watermelon and cantaloupe transplants.