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Poster: Biology & Disease Mgmt: Chemical Control


Increased frequency of multifungicide resistance in Botrytis cinerea
M. HU (1), G. Schnabel (1) (1) Clemson University, U.S.A.; (2) Clemson University, U.S.A.

Over four consecutive strawberry production seasons, resistance to 7 chemical classes of fungicides was determined for 2130 isolates from commercial strawberry fields located in South Carolina and 10 other states of the eastern United States. The overall frequencies of isolates resistant to thiophanate-methyl, pyraclostrobin, fenhexamid, boscalid, cyprodinil, iprodione, and fludioxonil increased over the four seasons to 84.7, 73.0, 32.2, 29.9, 29.7, 12.6, and 11.3%, respectively. Resistance to thiophanate-methyl was found virtually in every location. Resistance to fludioxonil was rarely found during the first three seasons, but increased to 11.3% in 2014-15. Our latest data from the 2015-16 season shows the frequency of resistance to fludioxonil has increased to 12.3%, indicating a strong selection for fludioxonil resistance in strawberry fields in the eastern United States. We hypothesize that the more FRAC codes are rotated into the spray program, the more we will select for isolates with increasing numbers of resistance determinants.