Differences in Epidemiology and Control of Lettuce Drop Caused by Sclerotinia minor and S. sclerotiorum. C. L. Patterson, Department of Plant Pathology, University of California, Davis 95616. R. G. Grogan, Department of Plant Pathology, University of California, Davis 95616. Plant Dis. 69:766-770. Accepted for publication 9 April 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-766.

Sclerotial inoculum was decreased and lettuce drop was eliminated after three consecutive years of roguing lettuce plants infected by Sclerotinia minor. Significant reduction of drop caused by S. minor was achieved by one application of DCNA, iprodione, or vinclozolin immediately after thinning. Apothecia of S. sclerotiorum were found in the late fall, winter, and spring in the San Joaquin Valley during prolonged wet periods. Effective control of S. sclerotiorum, therefore, is influenced by the timing of fungicide applications and the source of apothecia and ascospore inoculum. Because of the endemic occurrence of S. sclerotiorum in the San Joaquin Valley, two fungicide applications may be required for efficient disease control.