In Vitro and Field Comparison of Six New Fungicides with Iprodione and Vinclozolin for Control of Leaf Drop of Lettuce Caused by Sclerotinia sclerotiorum. M. E. Matheron, Extension Plant Pathologist, University of Arizona, Yuma Agricultural Center, Yuma 85364. J. C. Matejka, Research Assistant, University of Arizona, Yuma Agricultural Center, Yuma 85364. Plant Dis. 73:727-730. Accepted for publication 16 March 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0727.

In vitro and field studies were initiated to identify compounds having fungicidal activity against Sclerotinia sclerotiorum and potential for improving control of lettuce leaf drop. At a concentration of 0.5 ?g/ml, radial growth of the pathogen was significantly reduced by bitertanol, chlozolinate, diniconazole, iprodione, terbutrazole, vinclozolin, and CGA-449. At the ED₅₀ concentration of tested compounds, sclerotia production was reduced in the presence of diniconazole or SC-0858 and was increased in the presence of chlozolinate or iprodione. In field tests, levels of disease control equivalent to those provided by iprodione and vinclozolin were observed for at least 2 yr with diniconazole, CGA-449, and SC-0858. Potential new fungicides apparently exist for control of Sclerotinia leaf drop of lettuce, should iprodione and vinclozolin become ineffective in the future.