Divisi
Maize weevil
Sitophilus zeamais · Storage
Photo: Natasha Wright, Florida Department of Agriculture and Consumer Services, Bugwood.org · CC BY 3.0 us
The maize weevil (Sitophilus zeamais) is a small reddish-brown, long-snouted beetle — a storage pest that ruins cereals after harvest: maize above all, but also sorghum, rice, wheat and beans. Adults start boring into cobs as the crop dries down in the field, then breed explosively in a warm, humid store. The female drills into a single kernel and lays one egg inside; the grub grows hidden within the grain, eating it hollow before chewing its way out as a new adult — which is why a bag can look whole on top while it is being quietly emptied from within.
Frank Peairs, Colorado State University, Bugwood.org · CC BY 3.0 us
Why it matters
The maize weevil attacks the grain you have already grown, harvested and are counting on to feed your family and sell for cash — it can hollow out and spoil up to 40% (almost half) of everything you put in the store. The cruel part is that it works hidden inside the kernels: each grub eats a grain from the inside out, so the bag looks fine on top while it is quietly being emptied underneath. Once weevils are breeding inside the grain you cannot reach the grubs to kill them, and they carry over from one season to the next in leftover grain and in the cracks of the store. So the real battle is to stop them getting in — by storing your grain dry, clean and sealed.
When to act
any live weevils or fresh bore holes seen in stored grain during routine checks
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 maize weevil field guide
- Identify it
- Scout for it
- Control it
12 field-guide sections in the app
The full guide to maize weevil — 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 maize weevil?
The damage shows first. Look for small round holes bored in the kernels (like tiny gunshot holes), grain that feels light, hollow and powdery with a flour-like dust gathering in the bag, and kernels that crumble when you press them. Quick test: tip a handful into water — badly eaten grain floats because it is hollow inside. A heavily infested bag also warms up and turns damp, caked and mouldy.
When should I take action against maize weevil?
any live weevils or fresh bore holes seen in stored grain during routine checks
How do I control maize weevil?
Prevent it — start with grain that is bone-dry and clean (this is your strongest tool). Harvest as soon as the grain is mature and dry it hard: a kernel should be difficult to dent with a thumbnail and should crack, not squash, when you bite it. Then shell it and winnow out the chaff, dust and broken kernels — weevils breed fastest in damp grain and slip straight into powder and cracked grains.
Which crops does maize weevil affect?
Among the crops covered here: Maize, Rice, Sorghum, Wheat.
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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