Divisi
White rot
Stromatinia cepivora · Fungal
Photo: Jochen Kreiselmaier, Pflanzenschutzberater, Dienstleistungszentren Ländlicher Raum Rheinland-Pfalz (DLR Rheinpfalz) in Neustadt/Wstr. · CC BY-SA 4.0
White rot is a soil-borne fungal disease of the onion family — onions, garlic and leeks. The fungus survives in the ground for years as tiny, hard black grains (called sclerotia — think of them as long-sleeping fungus seeds). When you plant an allium in that soil, the roots wake them up; the fungus then rots the roots and the base of the bulb, killing the plant from below.
Jochen Kreiselmaier, Pflanzenschutzberater, Dienstleistungszentren Ländlicher Raum Rheinland-Pfalz (DLR Rheinpfalz) in Neustadt/Wstr. · CC BY-SA 4.0 
Elizabeth Bush, Virginia Polytechnic Institute and State University, Bugwood.org · CC BY 3.0
Why it matters
White rot is the disease that can finish a whole onion or garlic crop — in a bad, wet season it can take up to 80% of your harvest, and it rots bulbs even after you've lifted and stored them. The worst part is what it leaves behind: those hard black grains (sclerotia) sit in your soil and stay alive for many years — often 15 or more — waking up every time you plant onions or garlic there again. Once your plot is infested there is no spray that clears it, so the whole game is keeping it OUT and stopping it spreading.
When to act
Any plants collapsing with white mould and black sclerotia on the bulb; treat the plot as contaminated for years afterward.
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 white rot field guide
- Identify it
- Scout for it
- Control it
14 field-guide sections in the app
The full guide to white rot — 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 white rot?
The first thing you see: older, outer leaves turn yellow, then wilt and die back from the tip while the plant is still growing — usually in patches, a few plants together, not the whole row at once. The plant looks starved and comes out of the ground with almost no pull because its roots have rotted away.
When should I take action against white rot?
Any plants collapsing with white mould and black sclerotia on the bulb; treat the plot as contaminated for years afterward.
How do I control white rot?
Prevent first — this is where the battle is won. Only plant clean sets, seed and cloves from a source you trust, because the black grains ride in on infested planting material and soil. Keep known-good land clean: knock soil off tools, boots and tyres and don't let runoff or shared irrigation water carry soil from a sick plot to a clean one — the grains travel in mud and water.
Which crops does white rot affect?
Among the crops covered here: Garlic, Onion.
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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