The cabbage white is the most common reason a kale plant looks like lace by August. It is not the butterfly that does the damage but the caterpillars, and they feed for three to four weeks before they pupate. There are two species with different behaviour, and the difference decides where you should be looking.
Two species, two kinds of damage
| Large white | Small white | |
|---|---|---|
| Latin name | Pieris brassicae | Pieris rapae |
| Eggs | Yellow, in clusters of 20 to 100 on the leaf underside | Single, one at a time |
| Caterpillar | Yellow-green with black spots, feeds in groups | Plain green, feeds alone |
| Where it feeds | The outer leaves, from the edge inwards | Bores in towards the heart |
| How easily seen | Obvious at a glance | Almost invisible against the leaf |
The large white does the most visible damage but is easy to find. The small white is the one that ruins the crop, because the caterpillar sits inside the head and leaves droppings where you cannot reach.
When they fly
Expect two generations, in warmer regions sometimes three.
May to June: the first generation. Fewer butterflies and limited damage.
July to August: the second generation. This is when nearly all the damage happens.
Egg to caterpillar: 7 to 10 days.
Caterpillar to pupa: 3 to 4 weeks of feeding.
That means one check a week is too infrequent in July. The eggs hatch in between.
Netting is the only thing that holds
Insect netting works, but only if three things are right. This is where most people fail even though they do have a net.
Mesh of 1.3 mm at most. That stops the butterfly. To stop flea beetles and cabbage root fly at the same time, choose 0.8 mm.
The net must not rest on the leaves. The female lays eggs straight through the net onto whatever leaf is touching it. Stretch the net over hoops with at least 20 cm of air above the plants.
The edges go into the soil. Bury them or lay heavy planks along the whole edge. A 5 cm gap is enough to let a butterfly in.
Put the net on at planting, not when you see the first butterfly. If eggs are already under the net you have built the caterpillars a greenhouse.
Look for eggs on the leaf underside
Turn the leaves over twice a week from midsummer. Yellow clusters of oval eggs rub off with a thumb. It takes two minutes per plant and is the only measure that works before there are caterpillars.
If the caterpillars have already hatched: pick them off by hand in the morning while they sit still. Groups of young large white caterpillars can be removed with the whole leaf.
A trap crop
Nasturtium is more attractive to the cabbage white than the cabbage is. Sow a row of nasturtium a few metres from the brassicas and some of the eggs are laid there instead, and you can pull the plants up with caterpillars and all.
It does not replace the net but it lowers the pressure. Nasturtium is edible too, both leaves and flowers. Varieties are among our nasturtium seeds.
The parasitic wasp does part of the job
If you see a dead or sluggish caterpillar surrounded by small yellow cocoons, the parasitic wasp Cotesia glomerata has been at work. Its larvae have eaten the caterpillar from the inside and spun cocoons on the outside.
Do not remove them. Every cocoon becomes another wasp that goes looking for more caterpillars. It is also the reason to leave broad-spectrum pesticides out of the brassica bed.
What does not work
Crop rotation. Good against soil-borne fungal disease, useless against an insect that flies. The butterfly finds the cabbage anyway.
Aromatic plants on their own. Dill, marigolds and tomatoes cut the number of landings somewhat, but a female that is searching still gets there.
Hosing the plant down. The caterpillars stay put.
Netting put on in August. The eggs are already laid.
Which crops get hit
All brassicas: kale, Brussels sprouts, cauliflower, broccoli, white cabbage, kohlrabi, mooli, rocket and swede. Late in the season kale and Brussels sprouts take the worst of it, because they are still standing when everything else has been harvested.
If you need to resow after an attack, a late sowing of fast varieties works, because the pressure drops off in September. The whole range is among our brassica seeds, and the growing itself is covered in our articles on cauliflower and broccoli.
Author: Emma Vogiatzi
Fact checked by Erik Hoekstra
Last updated 2026-08-31