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Soybean mosaic virus
Soybean mosaic virus · Viral
Photo: Daren Mueller, Iowa State University, Bugwood.org · CC BY 3.0 us
Soybean mosaic virus is a soybean disease you cannot spray away. It rides in on infected seed and is then carried plant to plant by aphids (small soft-bodied sap-sucking insects) as they probe for food. It spreads in a non-persistent way — an aphid picks it up and passes it on within seconds of tasting a plant — so by the time you see it, it is already moving. Early infection is the most damaging: it shrinks pods, cuts seed number and leaves mottled, discoloured seed you cannot sell or plant.
Why it matters
This is a virus, so there is no spray that cures it — once a plant is infected it stays infected for life. A bad outbreak can cost you up to 40% of your harvest: fewer pods, smaller seeds, and mottled discoloured grain that fetches a poor price and can carry the disease into next season if you save it. It is hard to fix because it hides in your seed and is spread by aphids in seconds, so the only real defence is stopping it before it gets into the field.
When to act
No curative treatment; act pre-emptively on clean seed and aphid pressure, especially where seed-borne infection and aphid vectors are high.
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 soybean mosaic virus field guide
- Identify it
- Scout for it
- Control it
15 field-guide sections in the app
The full guide to soybean 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 soybean mosaic virus?
What you see first: on the young trifoliate leaves (the three-part leaves near the top), a patchwork of light-green and dark-green blotches — like a shadow pattern that will not wash off. This mottling is called mosaic, and it is the clearest early sign.
When should I take action against soybean mosaic virus?
No curative treatment; act pre-emptively on clean seed and aphid pressure, especially where seed-borne infection and aphid vectors are high.
How do I control soybean mosaic virus?
Prevent — best defence (resistant variety): plant a resistant or tolerant soybean variety where one is available for your area. This is the single strongest tool you have, stopping most of the disease before it starts — far more reliable than anything you can do once the crop is up.
Which crops does soybean mosaic virus affect?
Among the crops covered here: Soybean.
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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