Control of downy mildew in seed onion

Abstract

Downy mildew, caused by Peronospora destructor (Berk.) Casp., is one of the limiting factors in the production of onion seed in Rio Grande do Sul. Experiments were conducted at Pelotas, RS, Brazil, from 1980 to 1982 to evaluate the efficiency of different fungicides and to determine the best program for controlling the disease. Among the fungicides tested, a commercial mixture of Metalaxyl 10% + Mancozeb 48% (Metalaxyl/Mz) at 121.8 g and Metalaxyl 25% at 21.3 g a.i./100 l of water gave the best results, with almost 100% disease control. With the incorporation of Metalaxyl/Mz in the spray program, it was possible to reduce the number of fungicide applications from eleven to six, with consistent results.