Sensitivity of Sclerotinia homoeocarpa isolates from Georgia to propiconazole and other DMI fungicides

Abstract

Four hundred and forty-one isolates from six populations of Sclerotinia homoeocarpa were collected from creeping bentgrass golf greens in Georgia, and tested for sensitivity to the demethylation inhibitor (DMI) fungicide, propiconazole. Mean ED50 values for an unexposed population (baseline) and an exposed population were 0.0049 and 0.0283 µg ml-1propiconazole, respectively. Mean relative mycelial growth on two discriminatory concentrations was significantly (P=0.05) greater for isolates from the populations that had been exposed repeatedly to propiconazole than for isolates from the four unexposed populations. The effective period of control decreased linearly with increasing log ED50 value, ranging from a mean of 12.2 days for an isolate with an ED50 value of 0.075 µg propiconazole ml-1 to 28.2 days for an isolate with an ED50 value of 0.005 µg propiconazole ml-1. Based on this study, decreased in vitro sensitivity to propiconazole resulted in reduced dollar spot control.