The cabbage looper is one of three common green caterpillars that gardeners lump together as cabbage worms, alongside the imported cabbageworm and the diamondback moth larva. The looper is the easiest to identify by how it moves: it is smooth and hairless, light green with thin white stripes down the back, and it humps its midsection into a loop with each step, exactly like an inchworm. The adult is a mottled gray-brown moth that flies at dusk and lays single, pale eggs on the leaves.
How to identify a cabbage looper
Identification is satisfying and helps you scout, but the practical controls overlap heavily with the other brassica caterpillars, so do not let it slow your response.
The looping crawl is the giveaway. The fuzzy, velvety green caterpillar that crawls normally is the imported cabbageworm, the larva of the white butterfly. The smallest and squirmiest is the diamondback moth larva. For the full side-by-side picture and the shared toolkit, see the combined cabbage worms guide.
What the looper does and why early scouting wins
Young loopers feed on the undersides of outer leaves, which brassicas tolerate well. The trouble starts as they grow and move toward the growing point and into developing heads, where they feed in protected folds and leave frass that fouls the harvest. Catching them while small, and before they reach the head, is far easier than digging them out of a dense cabbage later.
How to control cabbage loopers, step by step
The plan
Cover from transplant
Put a floating row cover over the bed at transplant. Brassicas need no insect pollination, so the cover can stay on the entire crop, blocking the night-flying moths from laying eggs.
Scout leaf undersides
Check under leaves and in leaf folds every few days, focusing on the growing point and developing heads. Look for frass and chewed edges to find the well-camouflaged loopers.
Hand-pick what you find
Pull caterpillars off and drop them in soapy water. The green camouflage is good, so let the frass guide your eyes.
Use BT for outbreaks
A BT-based biological caterpillar control sprayed on the foliage handles heavy infestations and spares beneficial insects. Cover leaf undersides and reapply after rain.
Clean up after harvest
Remove old brassica stalks and leaves where pupae and moths shelter, to reduce next season's pressure.
Row cover is the cleanest defense for brassicas
Brassicas are an ideal crop for season-long row cover because they set their edible parts without insect pollination. A floating row cover over hoops from transplant onward keeps the egg-laying moths off entirely, which is far easier than fighting caterpillars in a dense head later.
Hand-picking and BT for what gets through
If moths got in before you covered, or you are growing uncovered, hand-picking plus a BT spray covers the rest. Gloves keep your hands clean while you part dense leaves and pick caterpillars from the growing points.
For pressure beyond what hand-picking can handle, a BT-based biological control is the standard organic option. It is a naturally occurring soil bacterium that affects only caterpillars that eat treated leaves, so it spares bees, ladybugs, and other beneficial insects. Spray the foliage the loopers are eating, including leaf undersides, reapply after rain, and apply in the evening to protect pollinators. We are describing the approach generally rather than recommending a specific product.
Which plants get hit, and how to plan
The whole cabbage family is on the menu. Cabbage, broccoli, and cauliflower are favorites, with loopers boring into heads, and kale, collards, and Brussels sprouts are heavily attacked on the leaves. Leafy brassicas tolerate outer-leaf damage well, so focus your effort on protecting the parts you harvest.
Timing helps you stay ahead of the moths, which are active through the warm months. Use the planting calendar for your ZIP to schedule spring and fall brassica plantings, and remember that a fall crop maturing in cool weather often faces lighter caterpillar pressure. Knowing your frost dates lets you time that fall planting so it heads up before hard freezes while dodging peak summer moth activity.
What is the difference between a cabbage looper and a cabbage worm?
Both are green caterpillars on brassicas, but they move differently. The cabbage looper is smooth and arches its back into a loop as it inches along, like an inchworm, and it is the larva of a brown night-flying moth. The imported cabbageworm is velvety and fuzzy, crawls normally, and is the larva of the white butterfly you see over the garden. A third pest, the diamondback moth larva, is smaller and wriggles when disturbed. The controls are the same for all three.
Can I leave a row cover on cabbage and broccoli all season to stop loopers?
Yes. Brassicas like cabbage, broccoli, kale, and collards do not need insect pollination for the parts you eat, so you can keep the cover on the whole crop. That makes exclusion the most effective single tactic against the looper, because it stops the moths from ever laying eggs. Just seal the edges so adults cannot get underneath.
Is BT effective and safe against cabbage loopers?
Yes. BT-based caterpillar controls are widely used in organic vegetable growing and affect only caterpillars that eat treated foliage, sparing bees and other beneficial insects. Spray leaf undersides where loopers feed, reapply after rain, and follow the label for any pre-harvest interval. Wash produce well before eating, paying attention to the inner folds of heads where loopers and frass hide.
How do I get loopers out of a cabbage or broccoli head?
Prevention beats extraction, so a row cover from transplant is the real answer. If loopers are already inside a head, soak the cut head in cold salted or vinegared water for several minutes, which makes hidden caterpillars float out, then rinse well. Inspect the inner folds where they hide along with their dark frass before cooking.
The bottom line
The cabbage looper gives itself away by its looping crawl, but it responds to the same plan as the rest of the brassica caterpillar complex. Cover the bed from transplant, which you can do all season because brassicas need no pollination, then hand-pick stragglers and reach for BT only when pressure spikes. Focus on protecting heads and growing points, time your plantings with the calendar to dodge peak moth season, and clean up after harvest to keep next year lighter.
