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High fungicide insensitivity and reciprocity of iprodione sensitivity in Botrytis cinerea populations from berry crops in the Pacific Northwest
J. E. ADASKAVEG (1), H. Forster (1), C. Clemens (2), S. Midboe (3). (1) Univ of California, Riverside, CA, U.S.A.; (2) Syngenta Crop Protection, Richland, WA, U.S.A.; (3) Whatcom Farmers Coop, Bellingham, WA, U.S.A.

High losses due to gray mold in berry crops in the Pacific Northwest led to an evaluation of sensitivity to commonly used fungicides in <i>Botrytis cinerea</i> populations. Isolates from raspberry fruit in nine locations collected in summer 2012 were resistant to fenhexamid (EC50> 0.5 mg/L), cyprodinil (EC50 > 0.5 mg/L) and boscalid (EC50 > 8 mg/L) at 100%, 0 to 50%, and 0 to 44.4%, respectively. Resistance to iprodione was low (EC50 < 1) to moderate (EC50 1 to 2 mg/L) and occurred in 0 to 40% of the isolates. The distribution and incidence of resistance for all fungicides was similar in 2013 samplings of overwintering sclerotia of the pathogen in the same locations. In two fields where fenhexamid was not used previously, however, only 14.3 to 18.7% of the isolates were resistant to this fungicide. Iprodione was not used since 1997 due to high resistance and crop failures. The low to moderate levels of resistance indicated that iprodione could be used again in a rotation once per season. In 2013, incidence of moderate to high resistance at nine raspberry, blueberry, and strawberry fields ranged from 0 to 28.8%, 0 to 71.4%, and 16.7 to 71.4% for fenhexamid, cyprodinil, and boscalid, respectively. No resistance to fludioxonil and chlorothalonil was found in any of the samplings. These results demonstrate regional differences in fungicide sensitivity among <i>B. cinerea</i> populations that probably reflect differences in fungicide usage patterns among growers.

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