Know Your Cabbage Caterpillars
Cabbages and other brassicas are a food source for the caterpillars of several species of moth and butterfly.1 The most common culprits in the garden are the large white and small white butterflies.2
Small white caterpillars are pale green with a body up to 2.5cm long.2 Large white caterpillars reach around 4cm and are yellow with black markings.2 Both can do serious damage fast.
The adult butterflies lay eggs from May to June and then again from July to September.2 This means you can find cabbage white caterpillars on your brassicas from late spring through to autumn.2
What Cabbage Caterpillars Actually Do
Caterpillars eat holes in the outer and inner leaves of brassicas.2 Left unchecked, they can quickly destroy a plant.3 Kale, broccoli, cauliflower, turnips, and swede are all at risk — not just cabbages.3
Cabbage whites lay their eggs on the leaves so that when the caterpillars hatch, they have an instant supply of food — your veg plants.3 The eggs are tiny and easy to miss at first glance.4
Cabbage white eggs are tiny, yellow, and laid in clusters.4 Catching them early, before they hatch, saves you a lot of trouble later in the season.
Net Your Brassicas First
The best method of protection is to prevent the butterflies from laying their eggs on your plants in the first place.3 Covering plants with horticultural fleece or fine netting stops butterflies reaching the leaves.2
Use insect-proof mesh netting propped up by hoops that are as high as the plants will grow, so the net can stay in place for the whole season.3 Bamboo canes topped with jars also work well as supports.3
For broccoli, cavolo nero, red Russian kale, and sprouts, hoops around 1.5m tall are about right.3 For cabbages, cauliflower, romanesco, turnips, swede, and curly kale, 60–70cm is usually fine.3
Check Leaves — Especially the Undersides
Even with netting in place, it pays to check plants regularly and pick off any caterpillars that do make it through.2 Look closely at the undersides of leaves, where eggs are often hidden.4
A quick squash or gentle scrape with a fingernail can save your brassicas from a caterpillar invasion.4 Make this part of your weekly garden routine from late spring onward.
If you are growing only a few plants, picking caterpillars off by hand is a manageable task.5 You can feed them to chickens or dispose of them in a bucket of water.5
Use Nasturtiums as a Trap Crop
Some gardeners plant nasturtiums close to their brassicas to serve as a sacrificial or trap crop — a plant grown specifically to lure pests away from the crop you want to eat.5 Nasturtiums, with their soft, fleshy leaves, are a favourite for caterpillars.5
You can move eggs and caterpillars from your brassicas to nasturtium leaves once you spot them.2 During the summer, cabbage whites tend to lay two or three times depending on the season, so keeping on top of this across all laying periods matters.3
Nasturtiums are also attractive plants in their own right, so they earn their place in the garden beyond just pest management.5 Plant them close to your brassicas so caterpillars have an alternative food source nearby.
Spray as a Last Resort
If caterpillars are already present, you can spray young caterpillars as they emerge.2 Always read the product label carefully before use.
Stick to products approved for food crops and follow local guidance on what is permitted in your area. Stick to products approved for food crops and follow local guidance on what is permitted in your area.
Combine Methods for the Best Results
Netting is your strongest first line of defence.3 Regular egg checks add a second layer of protection, catching what netting misses.4
A trap crop of nasturtiums gives caterpillars an alternative food source and draws them away from your edibles.5 Together, these approaches cover the full growing season without relying on any single fix.
Start before the first eggs appear — once caterpillars hatch and begin feeding, the damage adds up quickly.3 A little prevention in spring pays off right through to autumn harvest.
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