Divisi
Frogeye leaf spot
Cercospora sojina · Fungal
Photo: Maggilautaro · Public domain
Frogeye leaf spot is a fungal disease (Cercospora sojina) that is most damaging on soybean (and also spots tobacco). The fungus over-winters in old soybean stalks left in the field and hides inside the seed. In warm, wet weather it throws spores onto the leaves, where each spot makes more spores that rain and wind carry up onto the fresh top leaves. Cycle after cycle, the spots eat away the green, healthy leaf the plant needs to fill its pods, and can even blotch the pods and the seed you keep for next year.
Why it matters
Frogeye leaf spot robs your soybean of the healthy green leaf it needs to fill its pods, and a bad attack in a warm, wet year can take up to a third (30%) of your crop. It is hard to beat once it takes hold because it spreads fast up the plant in every rain, and it hides in your old stalks and even inside your saved seed — so it comes back next season before you even see it. Your best win comes from stopping it before it starts, not from chasing it once the top leaves are covered.
When to act
spots appearing on upper canopy leaves during flowering to pod-fill in warm, wet weather
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 frogeye leaf spot field guide
- Identify it
- Scout for it
- Control it
14 field-guide sections in the app
The full guide to frogeye leaf 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 frogeye leaf spot?
What you see first: small round spots scattered on the upper leaves. Each spot is about the size of a match-head to a small pea, with a grey to light-brown dead centre ringed by a dark reddish-brown border — like a little eye staring back at you. That eye-in-a-ring look is where the name frogeye comes from.
When should I take action against frogeye leaf spot?
spots appearing on upper canopy leaves during flowering to pod-fill in warm, wet weather
How do I control frogeye leaf spot?
Prevent it first — plant a resistant variety (your strongest, cheapest tool): choose a soybean variety bred to resist frogeye and suited to your area, and always plant clean, disease-free seed — never keep seed from a spotted, infected crop. Resistant seed is the single most reliable control and it costs you nothing extra at spraying time.
Which crops does frogeye leaf spot affect?
Among the crops covered here: Soybean, Tobacco.
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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