Divisi
Bacterial spot
Xanthomonas spp. · Bacterial
Photo: Scot Nelson · CC0
Bacterial spot is a warm-weather bacterial disease of tomato, pepper and chili. The germ rides in on infected seed and seedlings, then splashes from plant to plant in rain and overhead watering, thriving in warm, wet, humid weather. It shows as small dark greasy spots on the leaves and rough, scabby spots on the fruit — and once it is in your field it cannot be cured, only slowed.
Scot Nelson · CC0 
Scot Nelson · CC0
Why it matters
Bacterial spot can take up to half your crop. It scabs the fruit so you can't sell it, and strips the leaves so the sun scorches whatever fruit is left. The hardest part: once it is in your field there is no cure — copper and clean habits only protect the leaves and fruit that are still healthy, so stopping it early is everything.
When to act
Start copper protection when small dark water-soaked spots first appear on leaves or fruit in warm wet weather, since the disease cannot be cured once established.
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 spot field guide
- Identify it
- Scout for it
- Control it
13 field-guide sections in the app
The full guide to bacterial spot — 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 spot?
The first thing you see — leaf spots: tiny dark spots on the leaves, smaller than a match-head, that look wet and greasy. Hold a spotted leaf up to the light and the spot looks see-through — this greasy, water-soaked look is the giveaway. Each spot is dark brown to black with a yellow ring (halo) around it. Look first on the lower and inner leaves, and in the early morning when there is dew, when the spots stand out most.
When should I take action against bacterial spot?
Start copper protection when small dark water-soaked spots first appear on leaves or fruit in warm wet weather, since the disease cannot be cured once established.
How do I control bacterial spot?
Prevent it — resistant variety + a clean start: grow a resistant or tolerant variety if you can get one matched to your area (this is one of your strongest tools). Start with certified clean seed and healthy transplants — the disease comes in on infected seed and seedlings, so clean planting material is how you keep it out of the field in the first place.
Which crops does bacterial spot affect?
Among the crops covered here: Sweet pepper, Tomato.
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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