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Yam nematode
Scutellonema bradys · Nematode
Photo: Airypedia, via Wikimedia Commons · CC BY-SA 4.0
Yam nematode (Scutellonema bradys) is a tiny, thread-like soil worm that burrows into the outer flesh of yam tubers and causes dry rot. Too small to see with the eye, it is carried into each new season inside infected planting setts and in the soil, and it keeps multiplying in store — leaving a crumbly brown layer under the skin that ruins tubers for eating, market and seed.
Flixtey, via Wikimedia Commons · CC BY-SA 4.0
Why it matters
Yam nematode causes dry rot — a crumbly, light-brown decay just under the skin of your tubers. A bad attack can spoil up to 60% of your harvest (more than half), turning yams you meant to eat, sell or plant back into waste. It is hard to beat because the worm is too small to see, it hides deep inside the tuber and in the soil, and it rides into next season inside the setts you replant — so once it is in your seed yams and your land, it comes back year after year.
When to act
Dry-rot cracking and brown flesh found in cut-tests of tubers at or after harvest, or a history of dry rot in the plot; select clean setts before replanting.
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 yam nematode field guide
- Identify it
- Scout for it
- Control it
13 field-guide sections in the app
The full guide to yam nematode — 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 yam nematode?
The damage (what you see first): cut a tuber across and look just under the skin — a thin light-brown, dry, crumbly layer, like dry corky sawdust, is the earliest sign. Over time it darkens, deepens, and the skin cracks, flakes and peels.
When should I take action against yam nematode?
Dry-rot cracking and brown flesh found in cut-tests of tubers at or after harvest, or a history of dry rot in the plot; select clean setts before replanting.
How do I control yam nematode?
Plant clean setts (most important): cut your seed setts only from healthy tubers with no brown layer under the skin. Never replant a tuber that showed dry rot — recycling infected setts is the single fastest way the worm spreads onto fresh land.
Which crops does yam nematode affect?
Among the crops covered here: Yam.
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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