Divisi
Stem and bulb nematode
Ditylenchus dipsaci · Nematode
Photo: Ed Kurtz, Bugwood.org · CC BY 3.0
Stem and bulb nematode (Ditylenchus dipsaci) is a microscopic, thread-like worm — thinner than a hair — that lives and breeds inside the stems, bulbs and growing points of onion, garlic, beans, maize and potato. It bloats and twists young plants, turns bulbs soft with brown rings inside, then survives for years as a dry, dormant fuzz called 'eelworm wool' hidden in seed, cloves and crop trash. Because it travels mainly inside the very sets, cloves and seed you plant, this is a fight you win with clean planting material — not a sprayer.
Ed Kurtz, Bugwood.org · CC BY 3.0 
Howard F. Schwartz, Colorado State University, Bugwood.org · CC BY 3.0
Why it matters
Once this tiny worm gets into your onions, garlic or beans it can rot up to 60% of the crop — first in the field, then again in storage, where bulbs that looked fine collapse weeks after you lift them. The hard part is that you cannot see it: it hides inside the seed, sets and cloves you plant, and it can sleep in dry soil and crop trash for years. There is no spray that cures it — plant infested cloves, or into infested land, and you carry the problem into every new season. Winning means starting clean and keeping it out.
When to act
Presence in a field or seed lot; because it is seed- and soil-borne and hard to eradicate, act on clean planting material and rotation rather than a numeric count.
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 stem and bulb nematode field guide
- Identify it
- Scout for it
- Control it
16 field-guide sections in the app
The full guide to stem and bulb 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 stem and bulb nematode?
The first sign — bloat: young onion and garlic leaves and stems push up swollen, twisted, bent and stunted, often paler than the healthy plants around them; beans show thick, distorted stems. The plant looks puffed-up and deformed even though nothing has bitten it — it has swollen from the inside.
When should I take action against stem and bulb nematode?
Presence in a field or seed lot; because it is seed- and soil-borne and hard to eradicate, act on clean planting material and rotation rather than a numeric count.
How do I control stem and bulb nematode?
Prevent — start clean (your single strongest tool): plant only clean, certified nematode-free seed, onion sets and garlic cloves. 'Certified' means the material was officially tested and declared free of the pest. Never save your own seed, bulbs or cloves from a crop that showed any bloat. This one habit beats everything else, because the worm travels inside the planting material.
Which crops does stem and bulb nematode affect?
Among the crops covered here: Garlic, Maize, 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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