Powdery 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.
Wind-blown spores
Spores travel on air well beyond the affected bed, so a neighbouring garden can be the source. Spacing and airflow matter more than distance from your own infected plant.
It carries over to next season in soil, debris or seed — which is why rotation matters here, not just treatment.
Hot compost only
A heap that reaches and holds 55–65°C throughout will destroy it. A cool corner heap will not, and will return the problem to the beds with the finished compost.
When and where to look
Scout the planting while temperatures hold between 15°C and 28°C, with humidity above 60%. 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
Powdery mildew is a group of fungi affecting cucurbits, grapes, roses, squash and many ornamentals. Unusually, it thrives in warm, dry conditions with high humidity but does not need leaf wetness, making it common in late summer.
Symptoms
White to grey powdery coating on the upper surface of leaves and stems, later yellowing, curling and premature leaf drop. Fruit may be stunted or sun-scorched as the canopy thins.
Organic Treatment
Spray potassium bicarbonate, sulfur, or diluted milk solution at first signs; remove the worst leaves. Neem oil and Bacillus subtilis help slow spread. Improve airflow and sun exposure.
Chemical Treatment
Myclobutanil, tebuconazole, or trifloxystrobin on a 10–14 day schedule. Rotate chemistries and avoid sulfur in hot weather or on sensitive crops.
Prevention
Plant resistant varieties, space for airflow, prune dense growth, avoid excess nitrogen, and grow in full sun. Water at the base.
Crops at risk
Related problems
Powdery 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.