Halo Blight (Beans)
Risk near you, next 48h
See whether your local forecast favours this disease right now.
When it strikes
Remove affected material now
Take out the affected leaves, shoots or whole plants before the next wet spell, bag them as you cut, and wash your hands and tools before touching healthy plants.
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 16°C and 23°C, with humidity above 90%, after rain or heavy dew, while the leaves are still wet. Risk builds after roughly 8 unbroken hours of those conditions, so the morning after such a night is the moment to look.
The signs that lead here
Full problem lists for these crops
About
Halo blight (Pseudomonas savastanoi pv. phaseolicola) is a seed-borne bacterial disease of French and runner beans. It favours cool wet weather — unusually for a bacterial disease — and spreads explosively through a row when the foliage is worked while wet.
Symptoms
Small water-soaked spots on the leaf underside, each surrounded by a wide, pale yellow-green halo. Pods carry greasy, water-soaked patches that later ooze a cream-coloured bacterial slime. Badly infected young plants are stunted with distorted, yellowed growth.
Organic Treatment
Pull and destroy infected plants as soon as the halos are recognised, and never save seed from an affected row. Keep off the bean rows entirely while the leaves are wet.
Chemical Treatment
Copper sprays give partial protection to healthy foliage but will not cure infected plants. Commercial seed is treated with streptomycin in some countries; this is not available or permitted for garden use in the EU.
Prevention
Buy certified seed rather than saving your own, rotate beans on a three-year cycle, water at the base, space rows for airflow, and clear all bean debris after harvest.
Crops at risk
Related problems
Halo Blight (Beans) 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.