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Poster: Biology & Disease Mgmt: Chemical Control


Resistance of Botrytis cinerea to fungicides in California strawberries
S. COSSEBOOM (1), G. Schnabel (2), K. Ivors (1), G. Holmes (1) (1) Cal Poly State University, U.S.A.; (2) Clemson University, U.S.A.

Botrytis gray mold, caused by Botrytis cinerea, is a very destructive pre- and post-harvest fruit rot of strawberry that affects production worldwide. Resistance to foliar applied fungicides has been reported in many regions, including California. The objective of this study is to characterize the fungicide resistance of B. cinerea isolates from California. Approximately 800 isolates of B. cinerea were collected from four strawberry fruit production regions of California (Oxnard, Santa Maria, Salinas, Watsonville) (10 isolates per ranch, 10 ranches per growing region). Isolates were collected early season (minimal selection pressure) and late season (maximum selection pressure) during the 2015-2016 growing season. Using a previously described technique, sensitivity of each isolate was determined with a discriminatory dosage of each active ingredient: boscalid, cyprodinil, fenhexamid, fludioxonil, fluopyram, iprodione, penthiopyrad, and thiophanate-methyl. Preliminary data show individual isolates with resistance to one or more active ingredients and modes of action. While previous work in California has documented resistance to a few active ingredients in a few fields, this is the first comprehensive study of B. cinerea resistance to commonly used fungicides and modes of action. Results of this study will help identify ineffective fungicides and improve gray mold management programs.