How to get rid of cabbage worms on broccoli, cabbage, and kale

Cabbage worms are green caterpillars that chew ragged holes in broccoli, cabbage, kale, cauliflower, and Brussels sprouts. They can strip young plants and hide inside heads of broccoli and cabbage.

The good news is that cabbage worms are easy to control. Row cover keeps them off, and the caterpillars are easy to pick by hand.

What are cabbage worms?

“Cabbage worm” most often means the imported cabbageworm (Pieris rapae). It is the caterpillar of the cabbage white butterfly, the small white butterfly you see fluttering over your garden from spring to fall.

• The caterpillar is velvety green, up to about 1 inch (2.5 cm) long, with a faint yellow line down its back.
• The butterfly is white, with one or two black spots on each front wing.
• The eggs are tiny, yellow, and shaped like a bullet. They are laid one at a time on the undersides of leaves.

Two other caterpillars cause the same damage:

• Cabbage loopers are pale green with white stripes. They move by arching their backs into a loop.
• Diamondback moth caterpillars are small and wriggle fast when touched. They often drop from the leaf on a silk thread.

The controls below work on all three.

Signs of cabbage worms

• Ragged holes in leaves, starting on the outer leaves
• Dark green droppings at the base of leaves and inside heads
• Caterpillars along the leaf veins, where they blend in
• Holes chewed into broccoli and cabbage heads

Cabbage white butterflies have several generations a year. Expect cabbage worms from late spring until fall.

How to get rid of cabbage worms

1. Cover your plants with row cover

Row cover is the best way to prevent cabbage worms. If the butterflies cannot reach the plants, they cannot lay eggs.

Cover your plants right after you plant them. Tuck the edges into the soil or hold them down with rocks or sandbags. Broccoli, cabbage, and kale do not need bees to pollinate them, so you can leave the cover on all season.

Check under the cover now and then. If a butterfly got in, it can lay eggs where birds and wasps cannot reach the caterpillars.

2. Hand-pick the caterpillars

Check your plants every few days. Look along the leaf veins and on the undersides of leaves. Pick off caterpillars and drop them into soapy water. Rub off any yellow eggs you find.

3. Spray Bt

Bt (Bacillus thuringiensis var. kurstaki) is a natural bacterium that kills caterpillars. They stop feeding soon after they eat it and die within a few days. It does not harm people, pets, bees, or ladybugs.

• Spray both sides of the leaves.
• Spray in the evening, since sunlight breaks Bt down.
• Spray again after rain and every 7 to 10 days while caterpillars are active.

Bt works best on young caterpillars. Keep it away from plants where you want butterfly caterpillars, like dill and parsley.

4. Try spinosad for heavy outbreaks

Spinosad is made from a soil bacterium. It kills caterpillars and some other pests. It is toxic to bees while it is wet. Spray it in the evening when bees are not out, and only on plants that are not in flower. Read the label.

5. Welcome natural enemies

Tiny parasitic wasps lay their eggs inside cabbage worms. Birds eat the caterpillars too. Avoid broad-spectrum insecticides, which kill these helpers. Here is more on beneficial insects that eat garden pests.

How to clean broccoli and cabbage

Cabbage worms hide in heads and match the color of broccoli. Before cooking, soak broccoli and cabbage in cool salted water for about 15 minutes. The worms float out. Rinse and cook as usual.

Plants cabbage worms attack

Cabbage worms feed on plants in the cabbage family:

• Broccoli
• Cabbage
• Kale
• Cauliflower
• Brussels sprouts
• Collards, kohlrabi, and turnip greens

Other cabbage family pests

Cabbage worms often show up with other pests:

• Gray cabbage aphids cluster under leaves and inside Brussels sprouts. Spray them off with water. Read more about aphids on plants.
• Flea beetles chew tiny round holes in young leaves. Row cover keeps them off too.

For other common pests, see my guide to garden pests.