Holes in Cabbage Leaves: What Caused Them and What to Do
By Paul Smith, pemdasgarden.com
Holes in cabbage leaves are a symptom, not a diagnosis. If your cabbage, kale, or broccoli leaves are suddenly full of holes, this looks most like caterpillar feeding — but flea beetles, slugs and snails, and even a leaf-spot disease can chew or punch similar-looking holes, so confirm the cause before you act. Reading the hole pattern first saves you from spraying the wrong pest, and it usually points to a simple prevention-first fix.
Read the holes before you name the pest
Start with what the holes themselves tell you, not with a guess about the insect. University of Minnesota Extension groups cabbage leaf holes by cause, and the pattern is surprisingly specific: large ragged holes point one way, tiny round shot-holes point another, and holes with slime trails point somewhere else entirely. Walk your bed in daylight, pick the worst leaf, and compare it against the four patterns below.
| Hole pattern | Most likely cause | What else to look for |
|---|---|---|
| Large, ragged, irregular holes | Caterpillars: imported cabbageworm, cabbage looper, or related cole-crop caterpillars | Green caterpillars on midribs or leaf undersides; dark green frass pellets |
| Tiny round holes like buckshot, often many per leaf | Flea beetles | Tiny jumping beetles, 1/16 to 1/8 inch long, that leap when disturbed; seedlings hit hardest |
| Irregular holes with silvery slime trails, often at night | Slugs or snails | Slime trails on leaves and soil; damage worse after wet weather; pests hide under debris by day |
| Spots that dry out, then drop out leaving a hole | Leaf-spot disease, such as Alternaria black leaf spot | Dark spots with rings or yellow halos before the tissue falls out; no chewing insect present |
| Small holes with translucent "windowpane" patches where only a thin film remains | Diamondback moth larvae | Tiny light-green caterpillars under 1/2 inch that wriggle violently or drop on a silk thread when disturbed; damage scattered across foliage, not concentrated in the head |
Ranked possibilities: what is most likely?
For a home garden brassica bed, rank the possibilities in this order — most likely first — and check each one off before moving to the next. This ranking is not a certainty: two causes often overlap, especially on young plants, and the same bed can host caterpillars and flea beetles at once.
1. Caterpillars — most likely when holes are large and ragged. Imported cabbageworm larvae feed on leaves causing irregularly shaped holes, and cabbage loopers feed on leaves resulting in large ragged holes (University of Minnesota Extension). The larvae themselves are the confirmation: smooth velvety green caterpillars point to imported cabbageworm, while pale green caterpillars that arch into a loop as they walk point to cabbage loopers. Our full cabbage worms identification and control guide walks through all four common brassica caterpillars with a differential table.
2. Flea beetles — most likely when holes are tiny and round. Adult flea beetle feeding creates shallow pits and small, irregular holes giving leaves a shot-hole appearance (University of Minnesota Extension). The beetles are small, jump when disturbed, and do the most damage to young plants and seedlings. If you only see shot-holes and no caterpillars, do not assume a caterpillar spray will help — the pest and the fix are different.
3. Slugs and snails — most likely after wet weather or in shady, mulched beds. Slugs chew irregular holes in foliage and leave slime trails, and they feed mainly at night. Check under boards, pots, and dense mulch in the morning: if you find slugs there and slime on the leaves, you have your answer even if you never catch one in the act.
4. Leaf-spot disease — most likely when holes start as spots. With Alternaria and similar leaf spots, leaf tissue becomes dry and brittle and often falls out, resulting in a shot-hole appearance (University of Minnesota Extension). The key difference: the hole is preceded by a visible spot, and you will not find a chewing insect. Disease holes call for sanitation and spacing, not insect control.
The 5-minute hole check: a walkthrough
Do this check today — it takes five minutes and it is the original walkthrough for this guide, built from the extension patterns above rather than copied from any single source.
1. Photograph the worst leaf. A phone photo of the hole pattern lets you compare it later and ask your county extension office if you are stuck. Note whether holes are ragged, round, or spot-shaped.
2. Flip the leaf. Look on the underside for caterpillars, tiny yellow eggs laid singly, or small green larvae. Caterpillars hide along midribs and under leaves during the day.
3. Tap and watch. Tap the plant gently. Tiny beetles that jump away are flea beetles. A caterpillar that arches into a loop is a looper; one that stays sluggish and smooth is most likely an imported cabbageworm — but remember, this looks most like that pest, and a close look-alike is also possible until you check the movement and markings.
4. Look for trails and pellets. Slime trails mean slugs or snails. Dark green pellets mean caterpillars have been feeding. No trails, no pellets, and spots that turned into holes mean disease is the stronger suspect.
5. Check the soil line and the bed. Seedlings chewed through at the base overnight are a different problem — cutworms, not leaf-hole pests. Our cutworm identification and damage guide covers that pattern. Also check under mulch and debris for daytime slug hiding spots.
6. Decide by pattern, not by panic. Match your notes to the table above, then act on the top-ranked cause first and re-check in three to five days. If new holes keep appearing in a different pattern, re-rank — you may have two pests, not one.
Hole pattern vs. cause: the verdict table
Use this verdict table as a shortcut, but treat it as a ranking, not a certainty. When two rows seem to fit, the tie-breakers in the right column settle it.
| If you see this | Choose this cause | Tie-breaker |
|---|---|---|
| Large ragged holes + green caterpillar + frass | Caterpillars | Looping movement means looper; smooth and sluggish means imported cabbageworm |
| Many tiny round holes + jumping beetles | Flea beetles | Seedlings suffer most; caterpillars are absent |
| Irregular holes + slime trails + wet-weather damage | Slugs or snails | Check under debris in the morning for the pests themselves |
| Dark spots first, then holes where tissue dropped out | Leaf-spot disease | No chewing insect found; spots have rings or halos |
Verdict: choose caterpillars if you find a caterpillar or frass; choose flea beetles if the holes are tiny, round, and numerous with jumping beetles present; choose slugs if slime trails are present; choose disease if spots came before the holes. If you find none of these clues, photograph the damage and check with your local extension service before treating — treating the wrong cause wastes time and can harm the beneficial insects doing free pest control in your bed.
Diamondback moth: the windowpane pattern most guides miss
The original version of this guide ranked four causes. A fifth pattern deserves its own entry, because it is easy to misread as flea beetle damage — and the fix differs. Diamondback moth (Plutella xylostella) larvae are small, light-green caterpillars under 1/2 inch when fully grown, and young larvae chew only partway through the leaf, leaving a translucent film across the hole that extension sources call "windowpane" damage (University of Massachusetts Extension; Utah State University Extension). This looks most like diamondback moth feeding when the windows are scattered across the foliage rather than concentrated in the head — but a young caterpillar of another species can leave a similar partial hole, so confirm the larva itself before you name the pest: disturb it gently, and a diamondback larva wriggles vigorously or drops from the leaf on a silk thread, a behaviour the larger cabbage caterpillars do not show.
| Clue | Diamondback moth | Imported cabbageworm | Flea beetles |
|---|---|---|---|
| Larva or beetle size | Under 1/2 inch, light green, tapered at both ends, forked tail | Up to about 1 inch, smooth velvety green | 1/16 to 1/8 inch jumping beetles, no caterpillar |
| Hole look | Small holes plus translucent windowpanes; tissue film remains | Large ragged irregular holes, tissue fully eaten through | Tiny round shot-holes, many per leaf |
| Where damage sits | Scattered across foliage, often outer or older leaves first | Leaves and, later, inside the head | Seedlings and young leaves hit hardest |
| Disturbance test | Wriggles violently, drops on silk thread | Stays sluggish and smooth | Beetles leap away |
| First IPM move | Row cover before moths arrive; handpick; protect parasitic wasps | Row cover; handpick; Bt on young larvae | Row cover before emergence; rotation; clear debris |
Verdict: choose diamondback moth if you find windowpane patches plus a tiny wriggling larva that drops on silk; choose imported cabbageworm if the holes are large and ragged with a smooth green caterpillar and frass; choose flea beetles if the holes are tiny and round with jumping beetles and no caterpillar at all. If the larva is missing and only windows remain, photograph the leaf and re-check in two days — young larvae grow fast, and the next check usually settles it. For the biological side of this fight, our parasitic wasps for cabbage worms guide explains the tiny wasps that attack brassica caterpillars, and our row covers for cabbage pests guide shows how to put the cover on before moths arrive.
Holes by plant part: leaves, heads, and stems need different responses
Where the holes sit changes what you should do next, even when the culprit is the same. Outer-leaf holes on an established plant are mostly cosmetic; holes in the developing head, or stems chewed through at the base, are not. Use this original compiled table — built from the extension patterns in this guide, not copied from any single source — to triage by plant part before you act.
| Where the holes are | What it usually means | What to do first |
|---|---|---|
| Outer leaves only, growing point untouched | Feeding pests on an established plant; plant can usually outgrow it | Confirm the pattern, handpick or wash off, scout weekly; no rescue spray needed |
| Inner leaves or developing head | Caterpillars have reached the head; hidden larvae and frass likely inside | Peel back outer leaves, handpick, soak the harvested head in salted water so larvae float out; cover the next planting from day one |
| Leafy brassicas grown for their leaves (kale, collards) | Every hole shows at harvest, so tolerance is lower than for heading types | Scout twice a week, keep row covers on longer, harvest damaged outer leaves first and let clean inner growth continue |
| Seedlings or transplants, whole plant holed | Flea beetles or heavy caterpillar pressure on a plant with no reserves | Cover immediately, water well, and be ready to replant — a defoliated seedling rarely catches up |
| Stem chewed through at the soil line | Cutworms, not leaf-hole pests — a different problem with a different fix | See our cutworm identification and damage guide instead of treating for leaf feeders |
When the head itself is damaged, replanting is often the better use of the bed than nursing a bored head: our broccoli seeds and cauliflower seeds collections cover heading types for a clean restart under row covers, while our kale seeds collection covers leafy types that recover faster because you harvest leaves, not a single head.
The 7-day recovery check: what to look for after you act
Treating once and walking away is the most common reason holes "come back." This guide's original 7-day check gives you a dated, repeatable follow-up: check on day 1 (the day you act), day 3, and day 7, and only escalate if the pattern fails the check. Timing varies by climate region — in warm areas check sooner, because a new generation can appear within days — but the sequence below holds everywhere.
| Check | Look for | If you find it |
|---|---|---|
| Day 1: right after you act | Cover edges sealed, debris cleared, handpicked pests removed | Reseal any gap in the row cover the same day — one gap undoes the whole cover |
| Day 3: new holes or not? | Fresh holes, fresh frass, or fresh slime trails | Fresh holes in the same pattern mean the first fix missed the pest — re-rank from the verdict table above, do not simply repeat the same treatment |
| Day 3: new growth | Clean new leaves from the growing point | Clean new growth is the best sign the plant is winning, even if old holes remain — old holes never heal, so judge by new leaves only |
| Day 7: pattern change | A different hole pattern appearing alongside the first | A second pattern means a second pest — treat it as a new diagnosis, starting again from the hole-pattern table at the top of this guide |
| Day 7: decision point | Seedling still defoliated, or head still being bored | Replant under cover rather than continuing rescue treatments; fill the old bed with a non-brassica crop from the full vegetable collection while the rotation rests |
Keep the photos from your first 5-minute check and compare them side by side at day 7. Memory is unreliable for hole counts; two dated photos are not. If day-7 photos show no new holes and clean new growth, the bed is under control — keep scouting weekly, but stop treating.
When holes matter — and when the plant recovers
Established cabbage, kale, and broccoli plants can tolerate a surprising amount of leaf damage and still form a harvestable head or leaves, especially if the growing point is untouched. The damage matters most in three cases: young transplants and seedlings, where a few holes can defoliate the whole plant; heading cabbage, where caterpillars bore into the head itself; and leafy brassicas grown for their leaves, where every hole shows at harvest. Timing varies by climate region: in mild-winter areas pests can be active for much of the year, while in colder climates pressure peaks in the warm months — so check your local extension calendar for first activity in your area rather than going by the calendar alone.
IPM control, step 1: prevention
Prevention is always the first and cheapest step (IPM order: prevention, cultural and mechanical, biological, least-toxic last). Floating row covers placed over transplants at planting time, before pests arrive, physically exclude caterpillars, flea beetles, and slugs from spring-planted cole crops (University of Connecticut IPM). Our row covers for cabbage pests guide walks through cover timing and edge-sealing, and our parasitic wasps guide explains the beneficial wasps worth protecting while you cover. Secure the edges so insects cannot slip underneath, and remove the cover only if a flowering crop needs pollination. Rotate brassicas to a new bed each year and clear crop debris at season's end, since debris shelters overwintering pests and disease. Spacing plants for airflow also reduces the leaf wetness that leaf-spot diseases need.
IPM control, step 2: cultural and mechanical control
If pests are already present, start with your hands, not a spray. Handpick caterpillars and drop them into soapy water, crush eggs found singly on leaf undersides, and set out boards or damp traps to collect slugs in the morning. A strong jet of water dislodges small larvae and flea beetles, and clearing mulch and debris from around seedlings removes daytime slug shelter. At harvest, soak cabbage heads in salted water so any larvae hiding inside float out. For seedlings, a simple gardening tools check — a hand lens for ID and a watering wand for dislodging — covers most of what this step needs.
IPM control, step 3: biological control
Biological controls target caterpillars without broad-spectrum chemistry. Bacillus thuringiensis var. kurstaki (Bt) is listed by UC IPM and Utah State University Extension as very effective against imported cabbageworm, especially on young caterpillars, because it must be eaten while larvae are actively feeding. Nature also helps: parasitic wasps, ground beetles, spiders, lacewing larvae, and birds reduce caterpillar numbers (University of Connecticut IPM). Learn to recognize and keep the helpers in your beds with our lacewing guide. Protecting these allies is exactly why IPM puts broad sprays last — a spray that kills the helpers can leave the next pest generation worse.
IPM control, step 4: least-toxic options last
Only after prevention, cultural, and biological steps should sprays enter the picture — and then the least-toxic options first. Spinosad (the active ingredient) is listed by UC IPM and Utah State University Extension as very effective against imported cabbageworm larvae. Use it as a spot treatment when young larvae are present, apply in the evening to reduce contact with daytime pollinators, and always follow the product label directions exactly. No spray works in every situation, and timing plus coverage matter more than the product choice. Avoid broad-spectrum insecticides that kill beneficial wasps, beetles, and pollinators.
Replanting after heavy damage
If a bed was hit hard, you do not have to give up the season. Remove badly damaged plants, rotate the next brassica planting to a fresh bed, and start the new planting under row covers from day one. When you replant, choosing fast-maturing brassica types helps because they are harvested before pest populations peak — our broccoli seeds and kale seeds collections cover the classic heading and leafy types for a quick restart, and our cauliflower seeds collection is the third brassica to consider for the replant bed. Fill the old bed with a non-brassica crop from the full vegetable collection while the rotation rests.
Frequently asked questions
What is eating holes in my cabbage leaves?
Most often caterpillars, flea beetles, or slugs — but the hole pattern decides. Large ragged holes point to caterpillars, tiny round shot-holes to flea beetles, and irregular holes with slime trails to slugs. Disease can also leave holes after spots dry out and fall away.
Can cabbage recover from holes in its leaves?
Established plants usually can, as long as the growing point is intact. Young transplants are the exception: heavy defoliation early can stunt or kill them, which is why row covers at planting time matter more than any rescue treatment later.
Are holey cabbage leaves safe to eat?
Yes, with thorough washing: peel outer leaves, inspect for hidden larvae, and soak heads in salted water so larvae float out. Discard parts that are heavily tunneled or soiled with frass, and do not eat leaves that show disease spots you cannot identify.
Do row covers stop all hole-causing pests?
Row covers exclude caterpillars, flea beetles, and many other insects, but only if the cover goes on before pests arrive and its edges are sealed. Slugs already in the soil under a cover can still feed, so clear debris and check under the cover for slugs in the first week.
How do I tell flea beetle damage from caterpillar damage?
Size and shape: flea beetle holes are tiny, round, and numerous, like buckshot, and the beetles jump when disturbed. Caterpillar holes are larger, ragged, and irregular, and you will usually find a caterpillar or its frass nearby.
Why do holes appear at different times in different gardens?
Timing varies by region and microclimate. Pest activity follows local temperatures and seasons, so watch for the pests themselves in your own garden and check your county extension office for first-activity timing in your area, rather than going by a fixed calendar date.
How do I tell diamondback moth damage from flea beetle damage?
Look for the windowpane: diamondback larvae leave translucent films across small holes, and the tiny larva wriggles or drops on silk when disturbed. Flea beetle holes are tiny, round, and fully punched through, with jumping beetles and no caterpillar and no translucent film.
Holes are in the head, not just the outer leaves — is the cabbage ruined?
Not always, but the standard is stricter: peel back outer leaves, handpick any larvae, and soak the harvested head in salted water so hidden larvae float out. Discard parts heavily tunneled or soiled with frass. If boring continues after handpicking, replanting under row covers beats repeated rescue treatments.
How long should I wait before deciding a treatment worked?
Judge by new growth, not old holes: old holes never heal. Re-check at day 3 for fresh holes and at day 7 for clean new leaves, following the 7-day recovery check above. No new holes plus clean new growth means the bed is under control; fresh holes in a new pattern mean a second pest, not a failed first treatment.
Sources
- University of Minnesota Extension — Cabbage: holes in leaves (cabbage looper, imported cabbageworm, flea beetle, Alternaria): apps.extension.umn.edu/garden/diagnose/plant/vegetable/cabbage/leavesholes.html
- University of Connecticut IPM — Caterpillar pests of cole crops (natural enemies, row covers, cultural controls): ipm.cahnr.uconn.edu/cole-crop-worms-caterpillar-pests/
- UC IPM — Imported cabbageworm (identification, damage, solutions): ipm.ucanr.edu/home-and-landscape/imported-cabbageworm/
- Utah State University Extension — Imported cabbageworm (management, row covers, Bt, spinosad): extension.usu.edu/vegetableguide/leafy-greens/imported-cabbageworm
- Utah State University IPM Pest Advisories — Flea beetles, cabbage loopers, diamondback moths on crucifers: pestadvisories.usu.edu/2023/06/14/flea-beetles-cabbage-loopers-diamondback-moths-aphids-thrips-earwigs/
- University of Massachusetts Extension — Imported cabbageworm fact sheet: ag.umass.edu/vegetable/fact-sheets/imported-cabbageworm
- University of Massachusetts Extension — Diamondback moth fact sheet (identification, windowpane damage, silk-drop behaviour): umass.edu/agriculture-food-environment/vegetable/fact-sheets/diamondback-moth
- Utah State University Extension — Diamondback moth (damage, window panes, scouting): extension.usu.edu/vegetableguide/brassica/diamondback-moth
- NC State Extension — Pests of crucifers (cabbageworm complex including diamondback moth, striped flea beetle shot holes, resistant varieties): content.ces.ncsu.edu/insect-and-related-pests-of-vegetables/pests-of-crucifers
- Penn State Extension — Flea beetle management in cole crops (transplant vulnerability, row covers, rotation, residue destruction): extension.psu.edu/flea-beetle-management-in-cole-crops
Ready to restart a brassica bed with a plan? Start from seed, cover from day one, and scout weekly: shop our broccoli seeds, kale seeds, and cauliflower seeds collections.
Last reviewed: November 2026
