What to check first
Turn over the outer leaves
Look for small green caterpillars, eggs, and thin scraped areas that resemble windows. Later feeding makes larger ragged holes. Green larvae can blend into the leaf veins, so inspect slowly and use a photograph or magnifier if an insect’s shape is unclear. [1] [2]
Watch how a larva moves
A cabbage looper arches its body as it walks; other common brassica caterpillars move differently and vary in size. Identification helps explain damage and choose a labeled response, but you need not name every species before physically removing a clearly feeding caterpillar from a small crop. [1] [2]
Check the developing head or center
Examine the center of cabbage, broccoli, and cauliflower for chewing and fresh droppings. Injury there can affect the harvest more than several holes in outer leaves. Small transplants also have less foliage to spare than large established plants. [1]
Inspect covers and new transplants
Check plants before covering them so eggs or larvae are not enclosed with the crop. Look for loose edges, tears, or leaves touching gaps. Record whether damage began before or after the cover went on; a barrier cannot remove caterpillars already inside. [1] [2]
Choose the next step for your plant
Hand-remove a manageable population
Collect feeding caterpillars and inspect the same plants again several days later for missed larvae or newly hatched eggs. Preserve helpful predators and parasitoids where recognized. Keep enough outer foliage to support the crop instead of removing every leaf with a hole. [1] [2]
Prevent new egg laying and target small larvae if needed
Secure insect netting over clean plants, with room for growth and suitable ventilation. If larvae continue causing unacceptable damage, a labeled caterpillar product such as an appropriate Bt formulation may help when larvae are small and feeding. Follow crop, harvest, and application directions exactly. [1] [2]
What to avoid
- Do not wait for large caterpillars to tunnel into forming heads before inspecting.
- Do not use the fungus-gnat form of Bt as if every Bt product targets caterpillars.
- Do not cover infested plants and assume the netting will cure the problem.
What to watch next
Inspect at least weekly from planting, and every few days during an active outbreak. Track fresh chewing in the growing center and the presence of small larvae. If new holes appear without caterpillars, check after dark for slugs and ask Extension about other likely local pests.
Common questions
Can I keep netting over kale until harvest?
Often yes, because leaves are harvested before flowering and do not need pollination. Maintain ventilation and growing space, and inspect inside periodically. Seed production or nearby pollination-dependent crops need a different plan. [1]
Does seeing white butterflies mean the crop is already damaged?
White cabbage butterflies can signal a need to inspect for eggs and larvae, but it is the caterpillars that chew the crop. Look at the plants before applying a treatment. [1]
Sources and review
This guide was prepared with AI assistance and checked against the sources below. It has not been reviewed by a botanist. Conditions and plant responses vary; use the checks above to decide what applies. Read our editorial standards.
- University of Minnesota Extension: Caterpillars on cole crops
Cabbageworms, loopers and diamondback larvae feed on brassicas. Early scouting, hand removal and covers help; treatments work best on small caterpillars.
- University of Maryland Extension: Cabbage Looper on Vegetables
Young loopers create windowpane feeding before larger holes; inspect transplants and leaf undersides, remove larvae, and protect plants with covers.