Divisi
Early blight
Alternaria solani · Fungal
Photo: Clemson University - USDA Cooperative Extension Slide Series · CC BY 3.0 us
Early blight is a fungus (Alternaria solani) of tomato and potato. It survives from season to season on old infected debris, self-sown volunteer plants and dirty seed, and spreads by wind and by rain- and dew-splash onto the leaves. It goes for the oldest, most tired leaves near the ground first, then climbs the plant. Warm weather that swings between wet and dry, with heavy night dew, drives it hardest, and plants that are underfed or carrying a heavy load of fruit are the first to fall.
Dwight Sipler · CC BY 2.0 
Michal Maňas · CC BY 4.0
Why it matters
Early blight can strip up to half your crop (50%) when it takes hold. It rots the plant from the bottom up, killing the lower leaves so the plant can no longer feed its fruit or tubers, and it also puts dark sunken spots on the tomatoes and potatoes themselves, so even the fruit you save may not sell. Once the spots are climbing the plant it is very hard to push back, because the fungus is already living inside the old leaves and in the soil debris around the plant. Your best win is stopping it early — the first spots, on the lowest leaves — before it ever reaches the fruit.
When to act
Begin protectant sprays at first target-spot lesions on lower leaves, especially once plants start to set fruit and canopies stay wet.
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 early blight field guide
- Identify it
- Scout for it
- Control it
15 field-guide sections in the app
The full guide to early 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 early blight?
The first thing you see: small dark brown to black spots on the OLDEST, lowest leaves — the tired leaves nearest the ground. They start about the size of a pinhead and grow to the size of a small coin.
When should I take action against early blight?
Begin protectant sprays at first target-spot lesions on lower leaves, especially once plants start to set fruit and canopies stay wet.
How do I control early blight?
PREVENT first — grow a tougher crop and a cleaner field: plant tomato or potato varieties that carry early-blight tolerance where you can get them, and rotate — do not plant tomato or potato on the same ground two seasons running; give it 2-3 seasons in a non-related crop (maize, beans, cabbage) so the fungus in the old debris starves out.
Which crops does early blight affect?
Among the crops covered here: African nightshade, Irish potato, 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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