Divisi
Grey leaf spot
Cercospora zeae-maydis · Fungal
Photo: Daren Mueller, Iowa State University, Bugwood.org · CC BY 3.0 us
Grey leaf spot is a fungal disease of maize (caused by Cercospora zeae-maydis) that overwinters in old maize trash on the soil surface and attacks the leaves in warm, wet, misty weather. The veins of the leaf pen the fungus into long, straight-sided grey blotches that join up and kill the leaf. When the top leaves die before the grain is filled, the plant robs its own stalk to feed the cob, so stalks go weak and the maize falls over (lodges).
Bosh506 · CC BY-SA 3.0 
Corn and Sorghum Fungal Disease Laboratory · Public domain
Why it matters
Grey leaf spot kills your maize leaves from the tasselling stage onward, exactly when the plant needs every green leaf to fill the cob. In a bad, wet year on a susceptible variety it can take up to half your harvest (50%) and leave the stalks so weak they snap and fall over before you can pick them. It is hard to beat once it takes hold because the fungus lives on in the old maize stalks lying in your field, so it comes back season after season and, by the time you see the leaves greying, most of the damage to the canopy is already done.
When to act
Lesions present on leaves below the ear before or around tasselling on a susceptible variety in a humid, minimum-till field.
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 grey leaf spot field guide
- Identify it
- Scout for it
- Control it
16 field-guide sections in the app
The full guide to grey 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 grey leaf spot?
What you see first: small, pale, watery spots on the lower, older leaves — the ones nearest the ground. These start low because the fungus splashes up from the old maize trash on the soil, and the bottom of the plant stays wettest and mistiest the longest.
When should I take action against grey leaf spot?
Lesions present on leaves below the ear before or around tasselling on a susceptible variety in a humid, minimum-till field.
How do I control grey leaf spot?
Prevent it — plant a resistant variety (your strongest tool): in humid, high-risk areas choose a maize variety rated resistant or tolerant to grey leaf spot. This is the cheapest and most reliable protection — a resistant variety cuts the disease by roughly two-thirds and saves you from spraying at all in most years. Ask your seed supplier or extension officer which varieties are rated for it.
Which crops does grey leaf spot affect?
Among the crops covered here: Maize.
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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