Divisi
Cabbage webworm
Hellula undalis · Insect
Photo: Tonton Bernardo · CC BY-SA 3.0
Cabbage webworm (Hellula undalis) is the caterpillar of a small moth that attacks young brassicas — cabbage, kale, rape, cauliflower and radish. Instead of eating leaves from the outside, it bores straight into the growing point (the tender central bud) of a seedling and spins a mat of silk webbing over where it feeds. By killing that central bud it stops the plant from ever forming a head, or forces it to throw out several small useless heads. It hits hardest on nursery seedlings and freshly transplanted crops in hot, dry weather.
Ben Sale from UK · CC BY 2.0 
Ben Sale from UK · CC BY 2.0
Why it matters
Cabbage webworm goes for the one part of a young brassica the plant cannot replace — the central growing bud. Kill that and the plant will never make a proper head, so a bad attack in the nursery or just after transplanting can wipe out up to half your crop (50%). Because the caterpillar feeds hidden inside the heart under a shield of silk webbing, sprays struggle to reach it once it has bored in — so the damage is often done before you even notice. The only reliable fix is to catch it early, on the young seedling, before it tunnels deep.
When to act
webbing or larvae at the growing point of young seedlings or transplants
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 cabbage webworm field guide
- Identify it
- Scout for it
- Control it
14 field-guide sections in the app
The full guide to cabbage webworm — 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 cabbage webworm?
The damage first: look at the centre of the seedling, not the outer leaves. The tell-tale sign is a patch of fine silk webbing over the growing point, matted together with grains of green-brown droppings (frass) — like a tiny dirty spider's web sitting in the heart of the plant.
When should I take action against cabbage webworm?
webbing or larvae at the growing point of young seedlings or transplants
How do I control cabbage webworm?
Prevent it — start clean and grow fast: raise strong, healthy seedlings and get them to transplant quickly so they spend less time at the vulnerable tender stage. Cover nursery beds with fine netting to stop the moths laying eggs on your seedlings — this is your single best defence.
Which crops does cabbage webworm affect?
Among the crops covered here: Cabbage, Rape / covo / kale.
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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