US: Umass plant pathologists looking for downy mildew infected basil plants

Basil downy mildew was reported in Norfolk and Franklin Counties in MA this week. Although the downy mildew pathogen has been detected in basil seed, seed transmission is probably a rare event, and air-borne dissemination from infected plants is more likely. Infected leaves develop diffuse yellowing on the top of the leaf but distinctly veinbound patches on the bottom. When spores are produced, a characteristic gray, fuzzy growth on the underside of the leaves is evident. Control should focus on reducing humidity and leaf wetness period.

Few fungicides are labeled for herb plants and there are differences in registrations for field grown plants versus greenhouse plants. Copper products, phosphites, azoxystrobin, and mancozeb are labeled for use on basil. Plant pathologists at UMass are investigating methods to control this disease with biological control agents and are interested in collecting live, infected plants from residential gardens, greenhouses and field grown basil. If you think your basil plants are infected, please call or email Dr. Rob Wick at 413.545.1045, rwick@pltpath.umass.edu.