Small holes in kale or cabbage leaves are a sign to investigate, not an automatic reason to spray. The imported cabbageworm, a velvety green caterpillar of the familiar small white cabbage butterfly, is a common pest on brassicas. However, cabbage loopers, diamondback moth larvae, flea beetles, and other causes can produce confusing damage. Examine the undersides of leaves and the insects themselves before choosing a response. Early-season exclusion with an insect row cover, regular scouting, and hand removal often prevent losses in a small garden. When pressure is high, a crop-labeled product with Bacillus thuringiensis can target young caterpillars, subject to label and local rules.
Recognize the Imported Cabbageworm Life Stages
The adult imported cabbageworm is a small pale white butterfly, often with dark spots on its forewings. Females lay slender yellowish eggs on brassica leaves, including undersides. The larva is a soft-looking, velvety green caterpillar with faint longitudinal stripes, eventually growing to about an inch. University of Minnesota Extension documents these distinctive features. Butterflies flying over a bed are a warning to scout, not proof that destructive larvae are currently present. Damage comes from the feeding caterpillars, while adults sip nectar. Look closely before confusing beneficial insects or other non-feeding visitors with pests.
Read the Leaf Damage Before Choosing Control
Small irregular holes between leaf veins can expand as caterpillars grow. Green or dark fecal pellets near feeding areas provide another clue. Imported cabbageworms may hide on the main vein or undersides of leaves where their color blends into foliage. Large infestations can chew nearly all tender leaf tissue and contaminate developing cabbage or broccoli heads. Check interior leaves as well as obvious outside damage. Cosmetic holes on harvestable outer kale leaves may not justify aggressive action when larvae are absent. Young plants and heading crops have less tolerance for repeated feeding than vigorous mature leaves grown for immediate use. For a step-by-step method, see how to identify cabbageworms on kale and keep caterpillars off leaves.
Tell Cabbageworms From Similar Garden Pests
Cabbage loopers move by arching the body like an inchworm; diamondback moth larvae are generally smaller, more tapered, and can leave small window-like patches on brassica leaves. Flea beetles are tiny jumping beetles that produce many shot holes rather than the larger ragged chewing of caterpillars. University of Minnesota’s broccoli damage guide compares these patterns. Use a magnifying lens to inspect the actual insect rather than diagnosing by a single hole shape. Correct identification avoids treating a non-caterpillar pest with a microbial caterpillar product that will not solve the underlying issue.
Inspect New Leaves Every Few Days
Begin looking at plants from transplanting or shortly after seedling emergence, especially when white butterflies are active. Turn several leaves over on different plants instead of checking only the most damaged plant. Look for yellow eggs, tiny newly hatched larvae, larger velvet-green caterpillars, and fresh feeding holes. University of Minnesota recommends scouting at least weekly and more often as the season progresses. An easy routine is to inspect the top, mid-canopy and heart of each plant while watering. Write down what you actually find; a rising count of small larvae is a better reason to intervene than the sight of one butterfly.
Exclude Egg-Laying Butterflies With Row Covers
A lightweight insect barrier placed promptly over newly planted brassicas can prevent adult butterflies or moths from reaching leaves to lay eggs. Seal edges against the soil with appropriate weights and support fabric over hoops if plants would otherwise be pressed down. Inspect underneath before fastening: a cover can trap a population already present. Make room as cabbage heads and kale leaves grow. Remember that flowering vegetables needing insect pollination have different cover requirements; use covers appropriately for the crop’s stage. Row covers do not repel larvae already on leaves and must be maintained without large gaps.
Handpick Caterpillars in a Small Bed
With a few plants, hand removal is often the simplest targeted response. Check the upper and lower leaf surfaces, brush the larvae into a container of soapy water, and remove eggs if practical. Wear gloves if preferred and wash your hands after handling the garden. Look again several days later because new eggs can hatch after the first inspection. This intervention also protects parasitoids and predatory insects better than blanket spraying. Where there are large damaged leaves, assess whether trimming them would weaken the food-producing plant; unnecessary heavy defoliation can add stress to pest damage. Our walkthrough on how to identify rose sawfly larvae and stop windowpane leaf damage sets out each step.
Use Bt Only When Its Target Matches the Pest
Some products containing Bacillus thuringiensis subsp. kurstaki (Bt-k) target feeding caterpillars and work best while larvae are small. Maryland Extension lists Bt as effective for young imported cabbageworms. It does not reliably treat flea beetles, aphids, or an already damaged leaf that has no caterpillar present. Use only a pesticide product specifically labeled for your vegetable crop and target pest, and follow the entire label including protective equipment, harvest interval and any repeat-application requirements. Do not invent a universal mixing rate. Avoid spraying open flowers and drift onto non-target butterfly larvae.
Preserve Beneficial Insects Around Brassicas
Parasitic wasps, predators, pathogens and birds can naturally reduce some caterpillar populations. University of Minnesota describes multiple natural enemies on cole crops. Preserve that assistance by using the least disruptive method that actually meets the harvest-quality goal. Do not spray every green insect with broad-spectrum pesticides, which can remove helpers and create other pest problems. Nearby flowering habitat can support diverse insects, but it is not a guaranteed treatment for an established outbreak. Physical exclusion, scouting, selective hand removal and carefully labeled products work better as an integrated set than as an all-or-nothing promise.
Manage Crop Residue and Nearby Mustard Weeds
After harvest, remove or compost heavily infested plant debris appropriately; do not leave an entire patch of dying brassicas as an unmanaged refuge for pests. Weeds in the mustard family can also host cabbage-feeding caterpillars. University of Minnesota lists plants such as wild mustard and shepherd’s purse as alternate hosts. Avoid confusing every native flowering plant with a weed; identify local species first. Rotate crops as garden space allows and keep the immediate growing area free of unmanaged host plants. Good cleanup reduces pest resources but does not create a barrier against butterflies flying in from elsewhere. Our walkthrough on how to identify tomato hornworms and protect beneficial parasitic wasps sets out each step.
Decide When Leaf Holes Require Action
A few small holes on a vigorously growing kale plant may be manageable with monitoring, particularly if no caterpillars remain. Multiple small larvae on a newly planted cabbage row, fresh head penetration, or rapidly expanding feeding damage call for more immediate attention. Adjust your threshold to how you use the crop: a market-quality tight broccoli head may need greater protection than leaves you routinely trim and wash. Check whether row covers or handpicking can solve the problem before considering any pesticide. A green caterpillar found on an unrelated plant does not necessarily feed on brassicas or require removal.
Plan for Region, Weather, and Harvest Safety
The number of pest generations and peak butterfly activity differ between cool northern and warmer southern climates. Follow your local Extension service for seasonal monitoring advice and current products registered for use on edible crops. Before harvesting, inspect between cabbage leaves and broccoli florets; wash and prepare produce hygienically. For pesticide-treated plants, obey the label’s preharvest interval even if the leaves look clean. Keep garden chemicals away from children and pets, and never mix homemade pesticide recipes without sound evidence of crop safety. Prevention and correct diagnosis are more reliable than routine calendar sprays.
Related Guides
- How to Identify Cabbage Worms and Protect Brassicas With IPM
- How to Recognize Flea Beetles on Radishes and Protect Young Seedlings
- How to Identify Cabbage Looper Caterpillars on Broccoli Leaves
- How to Identify Cabbage Aphids on Broccoli Before Heads Fill
- How to Identify Cabbage Aphids on Kale and Manage Colonies
How We Research and Verify Gardening Advice
This guide was checked against the extension sources listed below on October 23, 2026. The first reference supplies the core procedure; other university sources help verify exceptions, botanical identification, and regional differences. We describe observation-based decisions rather than treating a USDA hardiness zone as an annual sowing calendar. The recommendations are educational, not a substitute for local diagnosis, current pesticide labels, or tested food-preservation recipes where these apply. VegWin has not claimed an affiliate relationship for any of the three guide links in this article. See our affiliate disclosure for site policy.
Sources reviewed (October 23, 2026): extension.umn.edu: cabbageworm larvae and eggs, scouting and physical and biological controls · extension.umd.edu: cabbageworm damage, row covers, handpicking and labeled Bt on small larvae · apps.extension.umn.edu: distinguishing feeding damage from cabbage looper and diamondback moth.
A velvety green caterpillar with faint pale lengthwise stripes, often hiding along a brassica leaf vein.
No. Inspect and clear plants first; covers mainly prevent new adult moths or butterflies from laying eggs.
No. Caterpillar-targeting Bt products do not control flea beetles, which are different insects.
No. Scout for eggs, larvae and meaningful feeding damage before deciding any action is necessary.
Often undamaged edible portions can be used after thorough inspection and washing, but discard spoiled produce and follow any pesticide label interval.