Caterpillars on Cabbage and Cauliflower: Hand-Pick, Nets and Bt
Small green worms and ragged holes in band gobi and phool gobi leaves are caterpillars, usually of the diamondback moth or the white cabbage butterfly, sometimes armyworms. In a home garden the winning combination is boring but reliable: look under the leaves twice a week, squash eggs and young caterpillars by hand, cover young plants with fine insect net, and keep a Bt spray (a bacterial product that affects caterpillars) in reserve for bad weeks. Here is how to tell who is eating your gobi and what to do about each.
In brief
- When: worst from October to December and again February to March in the plains, as winter brassicas grow
- Check: leaf undersides and the growing heart, twice a week
- First response: hand picking and squashing egg clusters
- Prevention: fine insect net over seedlings from transplanting
- Back up: Bt (Bacillus thuringiensis kurstaki) spray, aimed at young caterpillars
- Do not: spray broad spectrum insecticides that also kill the wasps and beetles eating your pests
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Which caterpillars eat cabbage and cauliflower?
| Pest | What you see | Clue |
|---|---|---|
| Diamondback moth | Tiny pale green caterpillars, under 1 cm; small holes and see through “windows” on leaves | Wriggles fast or drops on a silk thread when touched |
| White cabbage butterfly | Velvety green caterpillars up to about 3 cm; large ragged holes; dark green droppings | White butterflies flitting over the bed; yellow eggs |
| Armyworms | Darker, striped caterpillars feeding in groups, sometimes at night | Sudden heavy damage; egg masses covered in hairs |
| Cabbage looper type | Green caterpillars that arch their backs as they move | Feed in the open on outer leaves |
Damage to the growing point of a young plant matters most. UC IPM notes that feeding on the crowns of young plants can stunt them severely; holes in old outer leaves of a nearly mature head matter far less.
How do you get rid of green worms on cauliflower without poison?
- Look twice a week. Turn leaves over and peer into the heart, especially from transplanting until the head forms. Morning and evening are easiest.
- Squash eggs. Yellow bullet shaped eggs singly on leaves, or flat clusters, can be rubbed off with a thumb.
- Pick caterpillars into a cup of soapy water. Look for fresh droppings; the caterpillar is usually just above them.
- Shake young plants over a white sheet or tray; diamondback larvae drop on silk threads and are easy to see.
- Remove damaged outer leaves that are full of eggs, and destroy crop leftovers after harvest.
- Pull wild mustard and other cruciferous weeds nearby, which host the same pests.
The underside check that saves the crop
Set a phone reminder for two fixed days a week, say Sunday and Wednesday. Take a torch and check five plants fully, undersides included. If you find eggs or tiny caterpillars on more than one or two, do the whole bed that day. Small caterpillars are easy; big ones have already eaten the heart.
Do insect nets protect cabbage?
Yes. Netting keeps the moths and butterflies from laying eggs in the first place, which beats any spray. Use fine mesh insect netting (sold by nurseries and agricultural stores) over hoops of bamboo or wire, with the edges buried or weighed down with bricks so nothing crawls under.
- Put it on at sowing or transplanting, before the first eggs.
- Brassicas do not need insects for pollination, so the net can stay until harvest.
- Choose open, airy netting rather than heavy fabric in the plains, which can overheat plants on warm October and March days.
- Check under it now and then: a caterpillar that gets in has a pest free paradise.
What is Bt spray and does it work on caterpillars?
Bt is a product made from a natural soil bacterium, Bacillus thuringiensis, and the kurstaki strain acts on caterpillars of moths and butterflies. The caterpillar has to eat a sprayed leaf for it to work; it does not act by contact, so coverage of the leaf surfaces, including undersides, matters.
- Best on young caterpillars, which eat more relative to their size and are easier to kill.
- Spray in the evening or on cloudy days; the deposit wears off in strong sun and washes off in rain, so repeat after rain as the label allows.
- It is accepted in organic growing and is generally regarded as low risk to people, birds, bees and predatory insects. It will, however, kill any butterfly caterpillars it reaches, including wanted ones, so spray only affected plants.
- Resistance exists. Diamondback moth has become resistant to Bt in some areas. If it stops working, rely more on nets and hand picking, and ask your local agriculture extension office what works locally.
- Follow the label for mixing rate and any waiting time before harvest.
What about garlic, chilli and neem sprays?
Homemade garlic and chilli sprays mostly discourage soft bodied pests such as aphids, and may make leaves less attractive for a while. They do little against well fed caterpillars inside a head. The recipe and its limits are in our garlic chilli spray guide. Neem oil can deter egg laying and young larvae a little; treat it as a support, not the main defence.
Why not spray a strong chemical?
Broad spectrum insecticides kill the tiny parasitic wasps, ladybirds, spiders and hoverfly larvae that quietly eat cabbage caterpillars. UC IPM notes that using them can make diamondback moth worse by removing its natural enemies. On a vegetable you will eat in days, the risk to your family also outweighs the gain.
Is it safe to eat cabbage that had worms?
Yes. The leaves are safe once the caterpillars and their droppings are washed out. Cut the head in quarters, soak in salted water for 10 to 15 minutes, and rinse under running water; small caterpillars float out. Our guide to picking and cleaning gobi of hidden bugs covers kitchen cleaning in detail. Heads with rotting, slimy patches where caterpillars burrowed should be trimmed generously or discarded.
Start with nets and hand picking, which carry no risk. If you use Bt, neem or any other product, read the whole label, wear gloves and a mask, mix outdoors, and keep children and pets away until the spray dries. Never decant sprays into drink bottles. Observe the label’s harvest interval and wash produce well. Some sellers market strong chemical insecticides for vegetables; if you ever use one, follow the label exactly and use protective gear, and if anyone swallows a garden chemical or feels dizzy, short of breath or sick after spraying, go to a hospital immediately and take the container.
Cabbage and cauliflower caterpillar questions
How do I get rid of caterpillars on cabbage naturally?
Check undersides twice a week, squash eggs, pick caterpillars into soapy water, and cover plants with fine insect netting. Keep Bt spray as a back up for heavy outbreaks.
What are the small green worms on my cauliflower?
Most often diamondback moth or cabbage butterfly caterpillars. Tiny ones that wriggle and drop on a thread are diamondback; larger velvety ones are cabbage butterfly larvae.
Is Bt spray safe for bees?
Bt kurstaki is generally regarded as low risk to bees because it affects caterpillars that eat it. It does kill harmless butterfly caterpillars too, so spray only the plants that need it.
What is making holes in my cabbage leaves?
Usually caterpillars; look for green droppings. Shiny slime trails point to snails or slugs, and tiny round shot holes on seedlings point to flea beetles.
How do I protect cabbage from worms from the start?
Cover seedlings with fine insect net from transplanting, with the edges sealed, and keep cruciferous weeds out of the area.
When is the best time to spray Bt?
In the evening or on cloudy days, while caterpillars are young. Strong sun and rain shorten how long it lasts on leaves.
Why is Bt not working on my cabbage?
Caterpillars may be too large, coverage too thin, the spray washed off, or local diamondback moths may be resistant. Switch to nets and hand picking and ask your extension office.
Do garlic chilli sprays kill caterpillars?
Not reliably. They mainly deter soft bodied pests such as aphids for a short time.
Can I eat cabbage after finding worms in it?
Yes, after removing them and washing well in salted water and running water. Trim any rotten patches.
More organic pest help is in our Kitchen Garden section; for companion flowers that bring in caterpillar eating wasps, see companion planting for desi vegetables.