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POSTERS: Chemical control

Sensitivity of Sclerotinia sclerotiorum collected from the Mid-Atlantic region of the United States to six fungicide active ingredients
Habtamu Demissie - PhD candidate at the University of Maryland. Kathryne Everts- University of Maryland, College Park

Sclerotinia sclerotiorum causes white mold that can lead to high yield loss on lima bean in the Mid-Atlantic region. Control of the disease largely relies on use of fungicides. However, no studies have examined the regional population of S. sclerotiorum for sensitivity to labeled active ingredients (a.i.’s). In-vitro bioassays were conducted to determine the sensitivity of 40 S. sclerotiorum isolates to the a.i.’s boscalid, fludioxonil, cyprodinil, thiophanate-methyl, prothioconazole, and fluazinam. Each fungicide was diluted in dimethyl sulfoxide (DMSO) and amended to potato dextrose agar (PDA) at two concentrations. Three, 5-mm diameter plugs of S. sclerotiorum were transferred to 9-cm diameter plates amended with fungicide. The diameter of the radial growth was measured daily for 3 days. Data from each assay was analyzed separately. All fungicides significantly affected (P<0.0001) the radial growth of the isolates compared to DMSO+PDA control. The most effective a.i.’s in inhibiting mycelial growth were fludioxonil, which inhibited growth by 97% and 99% at 0.5 and 1.0 ?g a.i./ml, and thiophanate-methyl, which inhibited growth by 88% and 94% at 5.0 and 10.0 ?g a.i./ml, respectively, when compared to the control. Thiophanate-methyl (P=0.0122), but not other fungicide a.i.’s, inhibited radial growth differently among isolates, indicating that resistance to thiophanate-methyl may exist in the Mid-Atlantic S. sclerotiorum population.