Black Spot (Roses)
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.
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 18°C and 27°C, with humidity above 85%, after rain or heavy dew, while the leaves are still wet. Risk builds after roughly 7 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
Black spot (Diplocarpon rosae) is the most common and serious disease of roses worldwide, defoliating bushes through warm, wet summers and weakening them before winter.
Symptoms
Rounded black spots with feathery, fringed margins on leaves, surrounded by yellowing; affected leaves drop early, leaving bare canes.
Organic Treatment
Remove infected leaves and prunings, spray sulfur, copper or a baking-soda solution weekly in wet weather, and mulch to reduce splash.
Chemical Treatment
Myclobutanil, tebuconazole or chlorothalonil every 7–14 days during the infection season.
Prevention
Grow resistant varieties, space bushes, prune for an open centre, water at the base early in the day, and clear fallen leaves.
Crops at risk
Related problems
Black Spot (Roses) 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.