AGAR PLATE, SOIL PLATE, AND FIELD-EVALUATION OF FLUAZINAM AND OTHER FUNGICIDES FOR CONTROL OF SCLEROTINIA-MINOR ON PEANUT

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-mu-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-mu-g/ml or chlozolinate at 5-mu-g/ml, but 1-mu-g/ml of RH-3486, ASC-66825, or MON-13108 suppressed growth by 92, 90, and 54%, respectively. At 100-mu-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.