Sensitivity of Brazilian Botrytis cinereaisolates from strawberry to pyrimethanil and its control efficacy

Due to the significant losses caused by the pathogen Botrytis cinereain strawberry, the use of effective management is highly needed but can be difficult to achieve. Chemical control is the main method used against B. cinerea, but the pathogen has shown resistance to several fungicides worldwide. The fungicide pyrimethanil is registered for strawberry in Brazil, but it is still not widely used by growers in Paraná state. The objectives of this study were to evaluate the sensitivity of B. cinereaisolates to pyrimethanil, to verify possible cross-resistance between pyrimethanil and cyprodinil, and to evaluate the efficacy of pyrimethanil in controlling gray mold. The sensitivity of B. cinereaisolates to pyrimethanil was established based on the EC50of 100 isolates collected in the state of Paraná in 2017. EC50values of B. cinereafor pyrimethanil ranged from 0.0052 to 94.07 µg/ml with a mean EC50value of 6.53 ± 15.17 µg/ml. There was a positive correlation between pyrimethanil and cyprodinil EC50values (r= 0.83). The efficacy of preventive and curative applications of pyrimethanil, cyprodinil and fludioxonil was evaluated in detached strawberry fruit assays with sensitive and resistant isolates to pyrimethanil. Fludioxonil was the most effective in controlling the disease both isolates and application types. Pyrimethanil and cyprodinil showed greater efficacy when applied using sensitive isolate preventively, with control efficacy of 84.61 and 87.17%, respectively. Overall, pyrimethanil showed good efficacy in the control of gray mold of strawberry and can be recommended for managing the disease, but its use requires monitoring to avoid the selection of resistant isolates in the short term.