Downy Mildew
Risk near you, next 48h
See whether your local forecast favours this disease right now.
When it strikes
About
Downy mildew (various Peronospora and Plasmopara species) attacks cucurbits, grapes, basil, lettuce and onions in cool, wet weather. Unlike powdery mildew it needs prolonged leaf wetness and spreads explosively in humid spells.
Symptoms
Angular yellow patches on the upper leaf bounded by veins, with grey-purple fuzzy growth on the underside. Leaves brown and die from the inside of the plant outward.
Organic Treatment
Remove infected leaves, improve airflow, and apply copper preventively. Avoid overhead watering and water early so foliage dries fast.
Chemical Treatment
Mandipropamid, mefenoxam, or fosetyl-aluminium during cool wet periods, rotated with protectant copper or mancozeb.
Prevention
Choose resistant varieties, space widely, orient rows to prevailing wind, and irrigate at the base in the morning.