Common blight of beans identification & organic treatment
Xanthomonas axonopodis pv. phaseoli
How to identify common blight of beans
A warm-weather bean bacterium producing large, irregular brown leaf blotches with a narrow yellow border, distinct from halo blight's cooler-weather, wide-halo look.
Symptoms
- Large, irregular, water-soaked brown blotches on leaves with a thin yellow border
- Blotches often start at the leaf margin and spread inward
- Water-soaked, sunken spots on pods that can turn brown and crusty
- Heavily infected leaves shrivel and drop
Host crops
Bush bean, Pole bean.
How it spreads
Seedborne, spreads via warm rain and splashing water and on hands/tools when plants are wet.
Favorable conditions
Warm, humid weather (80-90°F) with frequent rain, warmer than halo blight's preferred range.
Progression
- Marginal leaf blotching (Warm, wet weeks) — Large brown blotches start at leaf edges.
- Leaf collapse (Following days) — Leaves shrivel and drop under heavy infection.
- Pod lesions (Wet weather during pod fill) — Sunken brown spots reduce pod marketability.
Organic treatment for common blight of beans
- 1. Copper bactericide · medium effort
Apply an OMRI-listed copper spray every 7-10 days starting at first symptom during warm, wet weather.
When: Onset through pod fill
- 2. Avoid wet-plant handling · low effort
Stay out of the bean rows when foliage is wet.
When: All season
Prevention
- Use certified disease-free seed.
- Rotate beans out of a bed for 2 years.
- Choose resistant varieties where available.
Easy to confuse with
- Halo blight (wide pale halo, cooler weather)
- Anthracnose of beans (sunken lesions with pink spore masses)
Terms on this page
- Spores / sporulation
- Spores are a pathogen's seeds. Sporulation is when it starts producing them, often as fuzz or powder you can see.
Sources
New to a word on this page? See the plain-English glossary.