Kale Cabbage Worms and Loopers: Causes and How to Fix It
Ragged holes chewed through kale leaves, with dark green droppings tucked into the crinkles, almost always mean caterpillars. A handful of related pests are responsible, and the same scouting-and-treating approach handles them all. Here's how to tell them apart and stop the damage.
Imported cabbageworm (the usual culprit)
What's happening
The velvety green caterpillar of the white cabbage butterfly — the small white butterfly you see fluttering over the bed. It chews irregular holes through the leaves and bores into the center of the plant, leaving moist green-brown droppings behind.
How to confirm
Look on the undersides of leaves and along the midribs for sluggish, fuzzy green caterpillars that blend in with the leaf. White butterflies hovering over the plants and dark droppings in the leaf crinkles confirm it.
How to fix it
Handpick caterpillars and drop them in soapy water — fast and effective on a few plants. For heavier infestations, spray Bt (Bacillus thuringiensis), a caterpillar-specific biological control, or use spinosad, coating both sides of the leaves; reapply after rain.
Prevent it
Cover the bed with floating row cover or insect netting at planting to keep the butterflies from laying eggs, and scout weekly through the season.
Cabbage looper
What's happening
A smooth green caterpillar that arches its back into a loop as it crawls, named for the inchworm motion. It feeds voraciously on the leaves, creating large, ragged holes and skeletonized patches.
How to confirm
Watch for the distinctive looping crawl and a caterpillar with a thin white stripe down each side, paler than the cabbageworm. Damage tends to be larger, more ragged holes than the cabbageworm makes.
How to fix it
Handpick what you can find, then treat with Bt or spinosad just as for cabbageworms — both work well on loopers when leaves are thoroughly coated. Repeat every 7 to 10 days while caterpillars are active.
Prevent it
Row cover excludes the egg-laying moths, and keeping the bed weeded removes alternate hosts that harbor them.
Cross-striped cabbageworm and diamondback moth larvae
What's happening
Smaller caterpillars that often feed in groups. Cross-striped worms have gray-blue backs with black bands; diamondback larvae are tiny, pale green, and wriggle backward when disturbed, riddling leaves with small shot-holes.
How to confirm
Many small holes rather than a few big ones, clusters of little caterpillars, and tiny larvae that drop and dangle on silk threads when you brush the plant point to these two.
How to fix it
Bt and spinosad control both; for diamondback in particular, rotate between the two since populations can build resistance to a single product used repeatedly. Spray in the evening and cover leaf undersides well.
Prevent it
Insect netting, crop rotation away from brassicas, and removing crop debris after harvest break their cycle.
When to worry (and when not to)
A few holes on an established, vigorous kale plant are cosmetic — outer leaves take the damage while the plant keeps producing, and you simply trim affected leaves. Worry when caterpillars are boring into the growing center, when young transplants are being defoliated faster than they can grow, or when populations explode across the bed. Caught early with handpicking, row cover, and a well-timed Bt spray, kale shrugs off caterpillar pressure and keeps cropping for months.