Holes in Kale Leaves: What’s Eating Them and How to Stop It
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Holes in kale leaves are usually the work of an imported cabbageworm, a green velvety caterpillar, so turn each leaf and handpick every worm today. White butterflies with one black spot per wing, flying at midday, are the adults laying eggs. Cabbage loopers raise their middles as they crawl and chew the same ragged holes. The leaf is still safe after a wash. Soak off the dark droppings, then eat the rest. One caterpillar can remove a lot of leaf in 48 hours.
Kale in the garden. Holes usually mean cabbageworms under the leaf, not a soil disease.
Quick answer
Large ragged holes, a green caterpillar, or dark green frass pellets mean imported cabbageworm or cabbage looper. Handpick the same morning. That evening spray Bacillus thuringiensis kurstaki on the leaves being eaten. Bt kills young caterpillars only. It does not kill flea beetles, slugs, or bees. Repeat in 5 to 7 days and after rain. Many tiny round holes on seedlings point to flea beetles, which jump when disturbed. Irregular holes plus a silver slime trail, with no caterpillar in daylight, point to slugs feeding at night. Name the pest before you pick a product.
Look under the leaf, then at the hole, then above the bed
Start on the underside of the newest damaged leaf, in morning light. Imported cabbageworms are green, close to the leaf color, often with a faint yellow stripe and a velvety coat. Young ones hide along the midrib. Cabbage loopers are green too, but they arch like an inchworm. Both leave dark green, rice-shaped frass. Fresh pellets and no insect means the worm is on the next leaf.
Second, read the hole. Caterpillars make uneven holes that join until veins remain. Flea beetles make many small round holes of similar size, mostly on seedlings, and they hop when the leaf is tapped. Slug holes are irregular and often low, on leaves that touch the soil. A slime trail may still shine early, before it dries.
Third, watch the row at midday. A white butterfly with a black spot is a cabbage white laying eggs. Eggs are pale yellow and stand on end under the leaf. More worms follow in about three to seven days. If you find no caterpillar, no jumping beetle, and no slime, look again an hour after dark.
Look on the underside of kale. Green caterpillars and dark frass settle the ID.
This is not your problem if
- Purple or yellow rings with no missing tissue point to nutrition or disease, not chewing.
- Every crop is shredded after one storm, with no frass or slime. Hail can do that in an afternoon.
- Only old yellow leaves are holed and the center is clean. Act if fresh frass shows this week.
- A huge horned caterpillar on a tomato is a hornworm. Still check the kale undersides.
Step-by-step: stop the feeding today
- This morning, check every underside. Pick caterpillars and pale yellow eggs into soapy water.
- If beetles jump or slime is present, do not stop at Bt. It kills caterpillars only.
- This evening, mix Bt kurstaki at the label rate. Monterey B.t. liquid uses 4 teaspoons per gallon. Spray it within 24 hours.
- Wet both sides of leaves being eaten. The worm must swallow it.
- Spray again after rain, or in 5 to 7 days while fresh frass shows.
- Once worms are gone, seal row cover if white butterflies are still flying. Cover blocks new moths, not larvae already inside.
- Soak leaves 5 to 10 minutes in cool water so frass floats off. The holes are not toxic.
- Recheck every other morning for two weeks. One missed worm does serious damage in 48 hours.
Match the hole to the pest
Use today's row, not last month's pest.
| Sign | Likely cause | Where to look | What to do |
|---|---|---|---|
| Ragged holes, dark pellets | Cabbageworm or looper | Undersides | Handpick; evening Bt; repeat in 5–7 days |
| Tiny round holes; it jumps | Flea beetle | Seedlings | Row cover; even water; skip Bt |
| Irregular holes and slime | Slug | Edges at night | Handpick; iron phosphate |
| White butterfly, black spot | Cabbage white adult | Above the row | Clear worms; seal cover |
| Pale yellow upright eggs | Next caterpillar wave | Under leaves | Crush eggs; Bt on new larvae |
| Lacy plant within 48 hours | Several half-grown worms | Plant center | Pick every size today |
Bt kurstaki for the caterpillars, and nothing else
For imported cabbageworm and cabbage looper, the fitting organic spray is Bacillus thuringiensis kurstaki. The caterpillar must eat a treated leaf. It then stops feeding and dies over a few days. A worm still sitting there the next morning does not mean failure. Judge the spray by whether new holes and fresh frass slow down.
Bt kurstaki does not kill flea beetles, aphids, slugs, or bees. It is the wrong tool for shot holes or slime. It also does less against a large caterpillar nearly done feeding, so keep handpicking. Spray in the evening, coat both sides, and reapply after rain and again in 5 to 7 days. Use the mix within 24 hours. Follow your bottle. Many liquid concentrates list 4 teaspoons per gallon. Renew a dust coat after rain too. Row cover prevents new eggs only if the edges meet the soil and the worms already inside are gone.
Kale hole chart: cabbageworm, flea beetle, and slug clues side by side.
Container plants versus in-ground beds
Kale in a pot is easier to search because you can turn it and see every underside. One missed caterpillar in a 5-gallon pot is a bigger share of the plant than the same worm in a 4-foot row, so check pots daily while butterflies fly. The Bt rate does not change. Skip wilted plants on a hot balcony wall. In a pot or a row, look again the morning after you see white butterflies, because new eggs land on both.
In-ground rows draw more cabbage whites. Seal row cover at every edge. Flea beetles like dry soil around seedlings. If you see slime, pull mulch back 3 to 4 inches from stems. Slugs climb a raised bed at night.
Myths that waste time
Myth: Any hole calls for a beetle dust.
Shot holes and caterpillar holes need different tools.
Myth: Bt kills on contact.
Caterpillars must eat it. Beetles, slugs, and butterflies do not.
Myth: Holed kale is unsafe to eat.
Chewing is not a toxin. Soak off the frass and eat the sound leaf.
Myth: Row cover removes worms already feeding.
It only blocks new butterflies. Pick and spray first, then cover.
Do this today / this week
- This morning, handpick caterpillars and eggs into soapy water.
- This evening, spray Bt kurstaki if frass or caterpillars are present.
- An hour after dark, look for slugs if you found slime and no worms.
- Tomorrow, soak sound leaves 5 to 10 minutes so frass floats off.
- Repeat Bt in 5 to 7 days, and again after rain.
- This week, if butterflies remain, seal row cover over a cleared bed.
Frequently asked questions
What should I do about holes in kale leaves if I only see frass?
Fresh dark green pellets mean a caterpillar fed recently and may have moved one leaf over. Search the undersides again. Handpick every worm and spray Bt kurstaki that evening on leaves being eaten. One missed worm keeps new holes opening for another day or two.
Are cabbageworms and cabbage loopers treated the same way?
Yes. Both are kale caterpillars, and both respond to handpicking plus Bt kurstaki. The looper arches as it crawls. The imported cabbageworm looks flatter and velvety. Repeat in 5 to 7 days, because new eggs can hatch after the first spray and rain washes the residue off.
Will Bt kurstaki harm bees on kale flowers?
Bt kurstaki affects caterpillars that eat treated leaves. It does not kill adult bees the way a broad contact spray can. Spray in the evening, when fewer bees fly, and coat the leaves being eaten instead of open flowers. Do not mix in another insecticide unless that label allows it.
Can I harvest kale the same day I spray Bt?
Many Bt kurstaki labels allow spraying up to the day of harvest, but read your bottle. When the leaves are dry, soak and rinse so frass floats off. Holes are not a safety problem. Throw out only tissue that is rotting or slimy.
Why did new holes show up a week after I sprayed?
A new hatch, a rain-washed spray, or a missed small worm can reopen holes within a week. Bt does not stop butterflies from laying. Handpick, then spray again 5 to 7 days after the first time. Cover the row if moths are still flying overhead.
Do flea beetles turn into large hole-makers later?
No. Flea beetles stay tiny, keep making shot holes, and jump when disturbed. Large ragged holes mean you should look again for a caterpillar and frass. Older kale usually outgrows light shot-hole damage on young plants if the soil stays evenly moist.
Key takeaways
- Imported cabbageworm and cabbage looper make most large holes. Check undersides the morning you see them.
- One caterpillar can ruin a lot of leaf in 48 hours.
- Spray Bt kurstaki in the evening. Repeat in 5 to 7 days and after rain. Many liquids use 4 teaspoons per gallon.
- Bt does not kill flea beetles or slugs.
- Seal row cover only after caterpillars already on the plant are gone.
