Effect of biocontrol and chemical strategies against lettuce drop caused by Sclerotinia sclerotiorum and S. minor in desert agroecosystems

• Published in: Phytopathology Vol. 98; no. 6; p. S38
• Main Authors: Chitrampalam, P, Turini, T A, Pryor, B M
• Format: Journal Article
• Language: English
• Published: 01.06.2008
• Subjects: Coniothyrium minitans; Paenibacillus polymyxa; Sclerotinia; Sclerotinia sclerotiorum
• ISSN: 0031-949X

Lettuce drop caused by both Sclerotinia sclerotiorum and S. minor is one of the most destructive diseases affecting lettuce in Arizona and California. Previous studies have shown that standard application rates (2-4 lbs/A) of the biocontrol product Contans (Coniothyrium minitans) was effective in controlling S. sclerotiorum, but not S. minor. In this study, high application rates of Contans and two isolates of the bacterium Paenibacillus polymyxa (strains 095 and 011) were tested for efficacy against Sclerotinia spp. and compared with the fungicide Endura. Field experiments were conducted at University research stations in both Yuma, AZ, and Holtville, CA. For Contans, product rates of 2 and 10 lbs/A were each applied twice. For P. polymyxa, suspensions of each strain of bacteria (10 super(9) cfu/ml) at a rate of 1 gal/A were each applied three times. Endura was applied at manufacture's rates. Results revealed that in trials against S. minor, two applications of high rates of Contans (10 lb/acre) and three applications of P. polymyxa-011 resulted in a statistically significant increase in the number of healthy heads and yields compared to control under high disease pressure. Other biocontrol treatments (P. polymyxa-095, Contans 2 lb) and chemical treatment (Endura) did not provide significant disease control. In trials against S. sclerotiorum, both rates of Contans, P. polymyxa-011, and Endura resulted in a statistically significant increase in the number of healthy heads compared to control under high disease pressure. In plots containing no disease inoculum, only P. polymyxa-011 resulted in a statistically significant increase in yield compare to control suggests growth enhancing aspects of P. polymyxa on lettuce.