A white butterfly barely more than an inch across, black-spotted at the wingtips, drifting over the cabbage patch: the cabbage white (Pieris brassicae) lays clusters of up to a hundred eggs on leaf undersides, and its caterpillars can strip a crop down to the veins. Act on the eggs early and the harvest survives.
Cabbage moth can completely destroy a harvest in the vegetable patch.
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Did you notice a white butterfly a little over an inch large (3 cm) fluttering around your cabbage? Think cabbage moth!
Take a closer look: you might find a hairy caterpillar… or a hundred!
This pest seeks most types of Brassica plants. It prefers all kinds of cabbage species, but you’ll find it on occasion on other host plants, too. For example, it loves nasturtium and, as in the picture at top, lavender.
In the United States, this caterpillar is called large white.
In the United Kingdom it goes by the name cabbage white or cabbage moth.
Actually, it isn’t a moth at all, but a type of butterfly!
Cabbage moth appears at various times over the year. Some years it appears in spring, in other years you might notice them only in summer or fall.
The white butterflies flutter to the undersides of cabbage leaves to lay eggs there. Once they hatch, tiny caterpillars start colonizing the plants, damaging them as they feed. Indeed, these caterpillars find cabbage leaves particularly appealing! Holes appear on the cabbage leaves.
Cabbage moth can devour an entire harvest in a single season.
How is this possible?
Simple math: 3 generations can fit during a normal growing season:
Female large whites seek out plants with dense leafage, and it’s even better when many plants are close together. A cabbage patch is ideal! It lays between 40 and 100 eggs in a neat pattern. Having so many caterpillars hatch together isn’t much of a problem for it since it specifically a place that has abundant food.
The cousin of Pieris brassicae, Pieris rapae, has an opposite strategy: a single egg per plant. That way, even measly, scraggly plants can also serve as host plants.
Because three generations fit into one growing season, the same pest comes back at you three times over. Knowing which wave you are looking at tells you what to search for on the leaves.
| Stage or generation | When | What you see | What to do |
|---|---|---|---|
| Overwintering pupa | Midwinter to late winter | Chrysalis tucked away in hidden places, nothing on the plants | Check that no dormant larvae are hiding before you rely on a net |
| First generation | Early to late spring | White butterflies fluttering to the undersides of cabbage leaves to lay | Scrape the egg clusters off with a knife as soon as you spot them |
| Second generation | Early to late summer | Holes appearing in leaves as tiny caterpillars colonise the plants | Spray Bacillus thuringiensis about 20 cm from the leaves if damage is serious |
| Third generation | Early to mid-autumn | Caterpillars still feeding on late cabbages | Use a decoction of chamomile, tansy, wormwood and common vervain |
Whichever wave arrives, preventive work means less damage and less effort later on.
Damage is variable, and essentially depends on how many caterpillars are chowing down on your cabbage plants. If you’re lucky, you’ll only have a few ugly but harmless holes in leaves, which won’t impact the harvest. However, an infestation of caterpillars can destroy all cabbage growth.
That’s why it’s better to work on preventive measures, since you’ll have less work and damage later on.
Young caterpillars feed together and strip the leaf down to its veins, leaving a lace-like skeleton.
There are quite a few organic cabbage moth treatments. It’s perfectly possible to treat against Pieris brassicae without using a single drop of toxic products.
Firstly, it’s common to try to protect your cabbage against this moth with a protective net. This is a solution that is only effective if you’re certain that no hibernating larvae are hiding, dormant, in the soil. If there were, a net wouldn’t help at all, since they’d already be inside!
Many plants repel cabbage moth: absinthe, lemon balm, mint, cosmos, sage, tomato, and also thyme herb, too. Planting these is really the best way to increase biodiversity in the garden, which, as a side effect, also helps produce different crops simultaneously!
You might be familiar with nasturtium. They’re often used as a decoy that attracts aphids. It’s the opposite of a repellent: it attracts pests away from other plants! This also works with cabbage moth: caterpillars will feast on nasturtium instead of cabbage.
As soon as you notice them, slice and scrape any eggs off the leaves with a knife. This certainly is a heavy chore if the infestation is severe, but it’s the only way to guarantee 100% healthy cabbages.
If ever caterpillars have started seriously damaging your heads of cabbage, the only option left is to spray them with Bacillus thuringiensis, which is an organic insecticide available in every garden store. Spray the product about 8 inches (20 cm) from the leaves, and spray again, if needed, a few days later.
Other natural options are also possible. We strongly recommend a decoction prepared from chamomile, tansy, wormwood and common vervain.
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Large white, as an adult, feeds on a great many types of flowers.
Interestingly, once an adult has tried a few types of flowers, it will usually only search those out for the rest of its life, even though it would be able to feed on many others.
For laying eggs, though, fewer plant species serve as hosts for this cabbage caterpillar – but these include a great many veggies! Sometimes the female will lay on the “wrong” plant, and the caterpillars will need to reach a new plant. Indeed, sometimes specific nutrients are missing that make it impossible for the caterpillar to transform into the adult butterfly form.
Buddleia (also known as butterfly bush), Nasturtium, Arabis, ornamental tobacco, wallflower (the European species)…
Brassica (cabbage, rutabaga or swede, mizuna, broccoli, milan cabbage, Brussels sprouts, cauliflower…), sea kale (Crambe maritima), certain Allium like garlic and onion, radish, turnip, arugula, watercress…
Practice companion planting: in particular, pairing cabbage with both celery and tomato plants will repel cabbage moth.
