Fall broccoli and kale can look healthy at breakfast and ragged a few days later. Small holes widen between the veins, green pellets collect in the center leaves, and pale green caterpillars disappear against the foliage. By the time damage is obvious from across the yard, the pests may be feeding inside the broccoli head or curled kale leaves.
The most useful rule is simple. Check fall brassicas before the holes become easy to see.
Why cabbageworm damage gets worse so quickly
The white butterflies moving around broccoli and kale are often adult imported cabbageworms looking for places to lay eggs. Their green larvae chew irregular holes and may leave the larger veins behind. Yet the caterpillar you find may be a cabbage looper or diamondback moth larva instead. The University of Minnesota Extension’s guide to caterpillars on cole crops shows the differences in size, movement, markings, and feeding damage.
Imported cabbageworms look velvety and move slowly. Cabbage loopers arch their bodies as they crawl. Smaller diamondback moth larvae often wiggle when disturbed. A fall bed may hold more than one species.
Damage matters most on young transplants and forming broccoli heads. Kale can keep growing after some outer-leaf chewing, but larvae near the growing point can damage tender leaves. Broccoli may lose enough leaf area to slow head development, and caterpillars or their droppings can work into the florets.
Do not confuse ragged caterpillar holes with every other chewing injury. Numerous tiny, round pinholes may point toward flea beetle damage, while larger missing sections at a leaf edge may call for a nighttime check for slugs or other feeders.
How to find caterpillars before they strip the leaves
Inspect plants at least twice a week while white butterflies or small moths are active. A quick look from above misses the places where eggs and young larvae usually hide.
- Turn over several leaves. Check lower leaves, inner leaves, and the undersides near the main veins.
- Look for eggs. Imported cabbageworm eggs are small, yellow, and usually laid singly. Looper and diamondback moth eggs are harder to distinguish without close inspection.
- Follow the droppings. Green or brown pellets on a lower leaf often mean a caterpillar is feeding directly above it.
- Check the center. Separate broccoli leaves gently and inspect around the developing head. On kale, look where new leaves meet the stem.
- Inspect edge and middle plants. Adults may enter at the bed perimeter, but checking only the outside row can miss an established pocket.
Utah State University Extension recommends inspecting transplants for eggs and larvae before planting because a cover placed over an infested plant can trap the pest inside. Its brassica caterpillar management guidance also supports hand removal and early use of row covers.
What to do when caterpillars are already feeding
For a small planting, start by handpicking. Hold a container under the leaf, remove each caterpillar, and check again the next day. Crush or remove visible eggs. Search below for larvae that dropped when the leaves moved.
A chewed leaf can still feed the plant if much of its green surface remains. Remove leaves that are badly shredded, yellow, diseased, or packed with droppings, but avoid stripping a young plant.
If repeated handpicking does not keep up, a product containing Bacillus thuringiensis var. kurstaki, often shortened to Bt, may be an option. The UC Statewide IPM guidance for imported cabbageworm lists Bt and spinosad among possible controls and notes that floating row covers can prevent egg laying. Bt must be eaten by young, actively feeding caterpillars, so timing and leaf coverage matter.
Before applying any pesticide, confirm that the label lists both the crop and the pest. Follow application rates, protective measures, and the required time between treatment and harvest. The EPA explains why pesticide label directions are legally enforceable. Avoid routine broad-spectrum spraying, which can kill predators and parasitoids that help suppress caterpillars.
How to keep new eggs off broccoli and kale
A clean, sealed insect barrier prevents adult butterflies and moths from reaching the leaves. Put the cover on immediately after seeding or transplanting, after you have inspected every plant. If caterpillars are already present, remove them before closing the bed.
Use hoops or a low frame so the cover does not press against the growing point or developing broccoli heads. Leave enough height and width for mature plants. Secure the entire perimeter with soil, boards, rocks, clips, or suitable ground fasteners. One loose corner can undo the rest of the setup.
Open the barrier only when you need to weed, inspect, or harvest, then seal it again. Broccoli and kale are harvested for leaves or heads rather than insect-pollinated fruit, so the cover can usually remain in place while the crop grows. Check underneath regularly because weeds, aphids, or a missed caterpillar can thrive inside a protected space. Utah State University Extension gives practical measurements and anchoring advice in its row-cover installation guide.
Which Dalen products fit this job
For a full garden row or a bed that needs custom coverage, the Dalen Insect Guard 5ft x 40ft Bug Blocking Garden Cover gives you 200 square feet of lightweight, reusable cover fabric. Its long format suits several broccoli or kale plants under hoops. Cut or position the material with enough extra at every side to close the ends and anchor the edges.
For a compact raised bed or a small group of plants, the Dalen Pop-Net Multi-Size Pop-Up Garden Screen Cover Pest & Hail Barrier creates a freestanding screen enclosure without a separate hoop tunnel. The screen allows sunlight, water, and air to reach the plants, and included stakes secure its corner loops. Choose the height that leaves room above the crop, and keep foliage away from the screen where possible.
Neither cover removes eggs or caterpillars that are already on the plants. Their job is to block the next round of egg laying after you clean and inspect the bed. That distinction is what makes the barrier useful instead of turning it into a shelter for the pest.
Adjust the plan for fall weather
Fall pest pressure does not end on the same date everywhere. Imported cabbageworms may remain active through much of the Upper Midwest growing season, while warmer regions may see adults well into fall. Base inspections on what is flying around the bed, not the calendar alone.
Warm afternoons can raise temperatures under some covers. Use insect mesh when exclusion is the main goal, and check for wilting or excess humidity. After heavy rain or wind, inspect every edge and reset shifted anchors.
Do not count on insect mesh as your only frost protection. If a cold night threatens, follow frost guidance for your region and use a cover rated for the expected temperature. Remove or reposition added frost material when conditions improve so the plants regain normal light and airflow.
At harvest, inspect both sides of kale leaves and the spaces between broccoli florets, then rinse the produce well. After the final picking, remove heavily infested crop debris rather than leaving pupae and shelter near the next brassica planting. A ten-minute leaf check now can save the part of the crop you actually want to eat.
