Divisi
Bacterial blight
Xanthomonas spp. · Bacterial
Photo: Howard F. Schwartz, Colorado State University, Bugwood.org · CC BY 3.0
Bacterial blight is a disease caused by Xanthomonas bacteria that attacks the leaves, stems and pods of beans, cowpea, cassava, rice and cotton. The germs ride inside the seed and splash from plant to plant in rain and irrigation water, slipping in through tiny wounds and the leaf's natural pores. In warm, wet, humid weather they multiply fast — and once they are inside a plant there is no cure, so the whole fight is about keeping the clean plants clean.
Donald Groth, Louisiana State University AgCenter, Bugwood.org · CC BY 3.0 us 
Scot Nelson · CC0
Why it matters
Bacterial blight can strip up to 70% — more than half your crop — in a warm, wet season, killing the leaves so the plant can no longer fill its pods or grain. The hard part is that once the germ is inside a plant, no spray can cure it — everything you do is to protect the healthy plants that are left. Worse, the germ travels inside the seed, so grain saved from a sick crop plants the disease straight back into next season. Catching the very first greasy spots early, and keeping your seed and field clean, is the whole game.
When to act
Act at the first water-soaked lesions during warm wet weather, as no cure exists once the bacterium is established; focus on protection and sanitation.
This guidance is general, compiled from published agronomic references including FAO and CABI. Thresholds and timing shift with your crop, your variety and the season.
In much of the region a spray is simply called mushonga — medicine. But a chemical group you cannot name is one you cannot rotate, and a product you did not write down has no pre-harvest interval you can observe. Mushonga, and other farming words →
The full bacterial blight field guide
- Identify it
- Scout for it
- Control it
14 field-guide sections in the app
The full guide to bacterial blight — every symptom to check, how and when to walk your field looking for it, and the controls that actually work, ranked. Built into your crop plan, so you are told to look before it costs you a harvest.
Crops it affects
Frequently asked questions
How do I identify bacterial blight?
The first sign: small water-soaked spots on the leaves — patches that look wet, greasy and see-through, as if a drop of oil or water is sitting under the skin of the leaf. Hold the leaf up to the sun: these spots glow translucent (light passes through them) with a greasy edge — that shine is the tell-tale of bacterial blight.
When should I take action against bacterial blight?
Act at the first water-soaked lesions during warm wet weather, as no cure exists once the bacterium is established; focus on protection and sanitation.
How do I control bacterial blight?
Prevent it first — plant clean, plant resistant: where a resistant or tolerant variety exists for your crop, grow it — this is your strongest and cheapest protection. Always plant certified disease-free seed, and never save seed from a field that had blight — the germ travels inside the grain and re-plants the disease straight into next season.
Which crops does bacterial blight affect?
Among the crops covered here: Cassava, Common bean, Cotton, Cowpea, Rice.
Catch it before it costs you a harvest
Divisi builds scouting into your crop plan — it tells you when to walk your field, what to look for at that stage, and what to do when you find it. Free for farmers, works offline.
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