Evaluation of the New Compound Oxathiapiprolin for Control of Downy Mildew in Basil

Patel, J. S., Costa de Novaes, M. I., and Zhang, S. 2015. Evaluation of the new compound oxathiapiprolin for control of downy mildew in basil. Plant Health Progress doi:10.1094/PHP-RS-15-0026. This study was conducted to evaluate a new chemical, oxathiapiprolin, as a seed treatment and foliar application for control of downy mildew of basil, caused by Peronospora belbahrii, and to assess the in vitro sensitivity of P. belbahrii to oxathiapiprolin. In the greenhouse, both foliar application and seed treatment with oxathiapiprolin significantly (P < 0.05) reduced downy mildew severity on basil and increased width of cotyledons compared to the non-treated control. In field experiments, foliar applications of oxathiapiprolin alone, as a tank mixture, or in alternation with azoxystrobin, potassium phosphite, or tea tree oil significantly reduced downy mildew severity and increased the basil yield compared to the non-treated control. In the laboratory test, EC50 values of sensitive P. belbahrii isolates ranged from 0.00033 μg/ml to 0.00040 μg/ml oxathiapiprolin, providing important information on baseline sensitivity of P. belbahrii to oxathiapiprolin. The results indicate that oxathiapiprolin can be applied as foliar applications in combination or in alternation with azoxystrobin or potassium phosphite to control the disease effectively.