Divisi
Fusarium basal rot
Fusarium oxysporum f. sp. cepae · Fungal
Photo: Howard F. Schwartz, Colorado State University, Bugwood.org · CC BY 3.0
Fusarium basal rot is a soil-borne fungus (Fusarium oxysporum f. sp. cepae) that attacks onions and garlic through the roots and the basal plate — the hard little disc at the very bottom of the bulb where the roots grow out. It loves warm soil and rots the plate upward into the bulb, killing the roots so the plant collapses. The fungus lives in the soil for many years and keeps rotting bulbs even after they are lifted and put in store.
Why it matters
Fusarium basal rot can take up to 40% of your onion or garlic crop — and the worst of it is hidden. Plants look sick above ground while the real damage is rotting the base of the bulb below, so you often only learn how bad it is when you lift the crop or open the store and find soft, spoiled bulbs. It is hard to beat because the fungus stays alive in the soil for many years: once your field is infected you cannot spray it out, you can only keep it from spreading and starving it of onions to feed on.
When to act
any plants yellowing and dying back with a soft, rotting basal plate found on lifting
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 fusarium basal rot field guide
- Identify it
- Scout for it
- Control it
15 field-guide sections in the app
The full guide to fusarium basal 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 fusarium basal rot?
The first thing you see: older leaves turn yellow from the tip downward and start dying back while the plant is bulbing, and the whole plant looks stunted and wilts in the heat of the day even when the soil is moist. A few plants collapse here and there across the bed.
When should I take action against fusarium basal rot?
any plants yellowing and dying back with a soft, rotting basal plate found on lifting
How do I control fusarium basal rot?
Prevent first — start clean. Plant only clean, healthy sets and seed from a trusted source (never save planting material from a field that had basal rot), and choose tolerant/resistant onion and garlic varieties where you can get them — these are your two strongest tools.
Which crops does fusarium basal 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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