A new race of downy mildew threatens spinach

Downy mildew, or blue mold of spinach, caused by the fungal pathogen Peronospora farinosa f.sp. spinaciae (= Peronospora effusa ), was observed on several spinach cultivars in the spring, summer, and fall of 1989 in California. Field observations in January 1990 revealed downy mildew in many spinach fields near Oxnard, Ventura County. The disease was also observed near Santa Maria in Santa Barbara County and King City in Monterey County, California, and near Winter Garden, Texas. In the spring of 1990, downy mildew was observed at several locations in the San Joaquin Valley (Stanislaus and Tulare counties). Our results indicate that a new race of downy mildew, race 4, is occurring on spinach in California and Texas. All cultivars tested were susceptible to race 4, including cultivars resistant to races 1, 2, and 3.