Poster Session: Fungicide Resistance

235-P

Sensitivity of Botrytis cinerea field isolates to the novel succinate dehydrogenase inhibitors fluopyram, penthiopyrad, and fluxapyroxad.
A. AMIRI (1), S. M. Heath (1), N. A. Peres (1)
(1) University of Florida, Wimauma, FL, U.S.A.

A recent monitoring of fungicide resistance in Florida revealed widespread resistance of Botrytis cinerea, the causal agent of Botrytis fruit rot (BFR) in strawberry, to almost all fungicides used for BFR control. If new alternatives are not implemented, growers may experience severe economic impacts. Fluopyram, penthiopyrad, and fluxapyroxad are three novel fungicides from the succinate dehydrogenase inhibitor (SdhI) group that are expected to be registered for BFR management. In this study, we determined the baseline sensitivity of 100 B. cinerea isolates to the three aforementioned fungicides and to the mixture of fluxapyroxad + pyraclostrobin (Merivon). EC₅₀ values based upon conidial germination ranged from 0.08 to 2.8, 0.67 to 9.03, <0.05 to 10.7 and 0.09 to 12.9 µg/ml, for fluopyram, penthiopyrad, fluxapyroxad and Merivon, respectively. Respective EC₅₀ values based on mycelial growth were 0.07 to 7.2, 0.09 to 6.8, 0.07 to 7.1 and 0.15 to 7.9 µg/ml. A positive cross-sensitivity was observed between the SdhI boscalid, to which resistance has been widely reported, and penthiopyrad (R² = 0.556) or fluxapyroxad (R² = 0.463) but not fluopyram (R² = 0.05). The three novel SdhIs sprayed preventively on strawberry fruits controlled all isolates regardless of their EC₅₀ values including those characterized previously as highly resistant to boscalid. Our findings show great potential for BFR control with the new SdhIs. However, as with all single-site fungicides, wise spray programs should be recommended when using these new molecules to avoid a rapid buildup of resistant populations.