Halo blight identification & organic treatment
Pseudomonas savastanoi pv. phaseolicola
How to identify halo blight
A bean-specific bacterium that produces small angular spots ringed by a wide, pale-green-to-yellow halo, often larger than the spot itself.
Symptoms
- Small, angular, water-soaked spots on leaves surrounded by a broad yellow-green halo
- Spots can merge, and the halo effect can make whole leaf areas look chlorotic
- Water-soaked, greasy spots on pods that may ooze a cream-colored bacterial residue
- Systemic infection can cause stunted, yellowed new growth
Host crops
Bush bean, Pole bean.
How it spreads
Seedborne, spreads via cool rain and splashing water, and moves on hands and tools when foliage is wet.
Favorable conditions
Cool, wet weather (60-75°F); unlike many bacterial diseases, halo blight favors cooler temperatures than common blight.
Progression
- Leaf spotting (Cool, wet weeks) — Angular spots with wide yellow halos appear.
- Systemic spread (As infection advances) — New growth may yellow and stunt from systemic infection.
- Pod infection (Wet conditions at pod set) — Greasy spots with bacterial ooze on pods.
Organic treatment for halo blight
- 1. Copper bactericide · medium effort
Apply an OMRI-listed copper spray at first sign and repeat every 7-10 days in cool, wet weather.
When: Onset through pod set
- 2. Avoid handling wet plants · low effort
Stay out of the bean patch when foliage is wet with dew or rain.
When: All season
Prevention
- Use certified disease-free bean seed; do not save seed from an infected planting.
- Rotate beans out of a bed for 2 years.
- Choose halo-blight-resistant varieties where available.
Easy to confuse with
Common blight of beans (narrower yellow margin, warmer weather), Bacterial brown spot.