Chocolate Spot (Broad Bean)
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 15°C and 22°C, with humidity above 90%, after rain or heavy dew, while the leaves are still wet. Risk builds after roughly 10 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
Chocolate spot (Botrytis fabae) is the main disease of broad beans in a wet spring. Overwintered crops in a still, damp, crowded row are the classic case: the mild form is cosmetic, but the aggressive form can kill a whole stand.
Symptoms
Small round chocolate-brown spots scattered over leaves, stems and pods. In the aggressive phase the spots merge into large black blotches, the stems blacken, flowers drop without setting and plants collapse.
Organic Treatment
Thin crowded rows and remove the worst-affected lower leaves to open the canopy. Keep the plants growing strongly — potassium-deficient and waterlogged plants are hit hardest — and clear all debris after harvest.
Chemical Treatment
A protectant fungicide such as chlorothalonil or tebuconazole at first symptoms, repeated in prolonged wet weather. Spraying after the aggressive phase has started rarely saves the crop.
Prevention
Sow thinly in well-drained, limed soil with good potassium, space rows for airflow, avoid sheltered damp corners for overwintered sowings, and rotate away from beans for three years.
Crops at risk
Related problems
Chocolate Spot (Broad Bean) 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.