Sensitivity to Metalaxyl and Screening of the Effective Fungicides of Phytophthora infestans in Hainan Province

PurposesTo clarify the sensitivity to metalaxyl of Phytophthora infestans isolates collected from Hainan Province and screen fungicides which have highly inhibitory activities and have high efficacy against P. infestans.

MethodsThe sensitivity of 132 isolates to metalaxyl was determined by leaf disc floating test, the inhibitory activity of 10 originals and 16 formulations of fungicides against P. infestans was determined on the detached leaves, and the efficacy of 9 fungicide formulations in controlling tomato late blight was determined in the field.

ResultsThe metalaxyl-resistant, intermediate and sensitivity isolates were 0, 95.5% and 4.5%, respectively.Metalaxyl, azoxystrobin, dimethomorph and metalaxyl-M·chlorothalonil 440 g/L SC, oxadixyl·mancozeb 64% WP, mandipropamid 23.4% SC had good inhibitory activity against P. infestans on the detached leaves of tomato. Metalaxyl-M·chlorothalonil 440 g/L SC and oxadixyl·mancozeb 64% WP had better control effect to tomato late blight in the field.

ConclusionsIntermediate isolates prevailed in the 132 isolates from Hainan Province, metalaxyl, dimethomorph and azoxystrobin have high inhibitory activity against P. infestans on detached tomato leaves. Formulations of metalaxyl, oxadixyl, mandipropamid and dimethomorph can be used to control tomato late blight.