Efficacy of Coniothyrium minitans on lettuce drop caused by Sclerotinia minor in desert agroecosystem

Field experiments were conducted over 2 years in Yuma County, Arizona and Imperial County, California, to evaluate if increased application rates of a commercial formulation of Coniothyrium minitans (Contans) were effective against lettuce drop caused by Sclerotinia minor. The efficacy of C. minitans at varied application rates were compared to two field isolates of Paenibacillus polymyxa and the chemical fungicide Boscolid (Endura). Two applications of manufacture recommended rate of Contans (2.2 kg/ha) did not significantly reduce the incidence of lettuce drop caused by S. minor, even though applications at this rate have been shown to be very effective in controlling lettuce drop caused by Sclerotinia sclerotiorum. However, two applications of high rates of Contans (6.6, 8.8, or 11 kg/ha), one at planting and one at post-thinning, significantly reduced the incidence of lettuce drop in most trials. Two isolates of P. polymyxa each applied at a rate of 9.4 L/ha (109 cfu/ml) were not effective in reducing the incidence of lettuce drop. Two applications of Endura, one at thinning and one at 4 weeks post-thinning, significantly reduced the incidence of lettuce drop in Yuma County, AZ, but not in Imperial County, CA. In summary, successful management of lettuce drop caused by S. minor in desert ecosystem could best be achieved with high application rates of C. minitans.