Downy Mildew
Risk near you, next 48h
See whether your local forecast favours this disease right now.
When it strikes
Treat, then re-check in 5–7 days
Pick off the worst material, apply the organic option below, and look again after five to seven days. If the spread continued, escalate rather than repeating the same treatment.
Rain and irrigation splash
Water splashing off soil and infected leaves carries it upward and along the row. Watering at the base and mulching the soil surface break the route.
It carries over to next season in soil, debris or seed — which is why rotation matters here, not just treatment.
Keep out of the compost
This survives a garden heap. Bag it for municipal green waste, which is composted industrially at temperatures a garden heap cannot reach, or burn it where that is permitted.
When and where to look
Scout the planting while temperatures hold between 10°C and 23°C, with humidity above 85%, after rain or heavy dew, while the leaves are still wet. Risk builds after roughly 6 unbroken hours of those conditions, so the morning after such a night is the moment to look.
Rule these out first
Same category, and at least one host crop in common — so they are genuinely confusable in the same part of the garden.
The signs that lead here
Full problem lists for these crops
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.
Crops at risk
Related problems
Downy Mildew risk by location
Each location has a month-by-month profile computed from the weather archive: how many hours a year actually meet this disease’s thresholds.