Divisi
Sweetpotato weevil
Cylas puncticollis · Insect
Photo: Graham Wise from Brisbane, Australia · CC BY 2.0
The sweetpotato weevil (Cylas puncticollis) is the single most destructive pest of sweet potato. The adult is a small, slender, ant-like black weevil with a long down-curved snout that feeds on the vines and lays its eggs in stems and in any storage root the soil leaves exposed. Its pale, legless grubs then tunnel unseen through the roots, and the plant fights back by filling even lightly-attacked roots with bitter, foul-smelling terpenes (natural defence oils) that make them unfit to eat or sell. Because the grubs work hidden inside the root and keep breeding after harvest, a light-looking attack in the field can become a ruined crop in the store.
Why it matters
Sweetpotato weevil is the most damaging pest of sweet potato — a bad attack can destroy up to 9 out of every 10 roots (90%), and it doesn't stop at harvest: the weevils keep breeding inside your stored roots. The worst part is that even a little feeding turns the whole root bitter and foul-smelling, so it can't be eaten or sold — a single grub can spoil a good root. And because the grubs work hidden inside the roots underground, by the time you see the damage the crop is already lost. That is why weevils are almost impossible to cure once they are established — your only real defence is to stop them ever reaching the roots.
When to act
Act on the first sign of adults, vine tunnelling or exposed cracking roots; because larvae feed hidden inside roots, low visible numbers already mean serious damage.
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 sweetpotato weevil field guide
- Identify it
- Scout for it
- Control it
15 field-guide sections in the app
The full guide to sweetpotato 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 sweetpotato weevil?
The damage you see first: cut open a suspect root and look for dark, winding tunnels packed with wet, sawdust-like droppings (frass) and small pale grubs inside. Even before you cut, the smell and taste give it away — weevil-damaged roots turn bitter with a sharp, turpentine-like odour, while a good root is sweet and clean. On the vines, look for rough, corky feeding scars and swollen, cracked stem bases, with the plants above them wilting, yellowing and stunted.
When should I take action against sweetpotato weevil?
Act on the first sign of adults, vine tunnelling or exposed cracking roots; because larvae feed hidden inside roots, low visible numbers already mean serious damage.
How do I control sweetpotato weevil?
Prevent it — start clean: the weevil rides into a new field on infested cuttings. Take your vine cuttings only from a clean, weevil-free field, and take them from the tips (the weevil lives lower down, near the old roots). Better still, get cuttings from a nursery well away from last season's sweet potato.
Which crops does sweetpotato weevil affect?
Among the crops covered here: Sweet potato.
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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