Agar Plate, Soil Plate, and Field Evaluation of Fluazinam and Other Fungicides for Control of Sclerotinia minor on Peanut. F. D. Smith, Research Associate, Tidewater Agricultural Experiment Station, Virginia Polytechnic Institute and State University, Suffolk 23437-0099. P. M. Phipps, and R. J. Stipes. Professor of Plant Pathology, Tidewater Agricultural Experiment Station, Virginia Polytechnic Institute and State University, Suffolk 23437-0099; and Professor of Plant Pathology, Department of Plant Pathology, Physiology, and Weed Science, Virginia Polytechnic Institute and State University, Blacksburg 24061-0331. Plant Dis. 75:1138-1143. Accepted for publication 7 May 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-1138.

The sensitivity of Sclerotinia minor to three dicarboximide fungicides (chlozolinate, iprodione, and vinclozolin), fluazinam (ASC-66825 and RH-3486), and MON-13108 was tested on fungicide-amended, glucose-yeast extract agar (GYEA). ED₅₀ values (dose for 50% inhibition of mycelial growth calculated from a dose-response line) for a field isolate (S-2) were 0.004, 0.004, 0.025, 0.08, 0.18, and 0.38 ?g/ml for ASC-66825, RH-3486, MON-13108, vinclozolin, iprodione, and chlozolinate, respectively. An in vivo, dicarboximide-resistant isolate (B-83-T2) exhibited enhanced mycelial growth on GYEA with either iprodione or vinclozolin at 1 ?g/ml or chlozolinate at 5 ?g/ml, but 1 ?g/ml of RH-3486, ASC-66825, or MON-13108 suppressed growth by 92, 90, and 54%, respectively. At 100 ?g/ml, vinclozolin, iprodione, and chlozolinate inhibited growth of isolate B-83-T2 by 93, 83, and 74%, respectively. When cultures of S. minor on a soil-cornmeal medium were sprayed with fungicides to simulate an application rate of 1.12 kg a.i./ha, MON-13108 was the only treatment that did not greatly inhibit mycelial growth of isolate S-2. ASC-66825 and RH-3486 significantly suppressed mycelial growth of isolate B-83-T2 in soil plate tests. In replicated field trials, ASC-66825 and RH-3486 limited disease incidence and increased yield of peanuts (Arachis hypogaea) more than other fungicides.