Divisi
Yam mosaic virus
Yam mosaic virus · Viral
Photo: Andikan Efiok Eduok, CC BY-SA 4.0, via Wikimedia Commons · CC BY-SA 4.0
Yam mosaic virus (YMV) is the most damaging virus of yam, hitting white and water yam hardest. It is a potyvirus: it hides inside infected setts (the seed tubers you plant) and is carried plant-to-plant by aphids. Because it lives inside the plant, no spray can cure it — and every season you save seed from sick plants, the disease builds up and your yields fall further.
Why it matters
Yam mosaic virus is a hidden thief. A bad infection can steal up to 60% of your tuber harvest — you dig up small, few tubers from vines that never grew strong. The worst part: once a plant is infected there is no cure and no spray that fixes it, because the virus lives inside the plant. And because it travels inside the seed tubers (setts) you save and replant, it gets worse every year you recycle seed from sick fields. Your only real weapons are clean planting material and pulling out sick plants early.
When to act
Mosaic symptoms on young vines, or aphid activity in a crop grown from unselected setts; rogue symptomatic plants early.
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 mosaic virus field guide
- Identify it
- Scout for it
- Control it
14 field-guide sections in the app
The full guide to yam mosaic virus — 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 mosaic virus?
The first sign — the leaf pattern: look at the young leaves. A healthy yam leaf is one even green. An infected leaf shows a mosaic — patches of light green and dark green mixed together like a shadow map, or a cloudy mottling you notice most when you hold the leaf up to the light.
When should I take action against yam mosaic virus?
Mosaic symptoms on young vines, or aphid activity in a crop grown from unselected setts; rogue symptomatic plants early.
How do I control yam mosaic virus?
PREVENT — this is where you win (start clean): the strongest tool you have is clean seed. Select and plant setts only from healthy, vigorous, symptom-free vines you watched last season — never save seed from a plant that showed mosaic. Where you can get it, plant certified clean or tissue-cultured seed yam (lab-grown, virus-free planting material). Starting clean is far more powerful than anything you can do once the crop is sick.
Which crops does yam mosaic virus 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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