Proven organic strategies for controlling cabbage looper.
Widely distributed throughout North America, the cabbage looper (Trichoplusia ni) chews large, irregular holes in the leaves of cabbage or cole crops (broccoli, cauliflower, kale, turnip). As it feeds it may bore into the center of heads and contaminate them with its fecal pellets. Caterpillars are most damaging during the last few days of their development.
Loopers are most easily recognized by their unique method of movement in which they double up or “loop” as they inch along. They are also called “inch worms” because of this trait. Larvae are large (1-1/2 inch long), pale green caterpillars with a narrow white stripe along each side and several narrow lines down the back. Adults are night-flying, gray moths (1-1/2 inch wingspan) with a silvery, V-shaped spot in the middle of each forewing.
Winter is spent as a pupae attached to host plants or nearby garden debris. Moths emerge in the spring and soon deposit pale green eggs on the plants. The eggs hatch in 3 or 4 days, and the destructive larval stage reaches full development in 2-4 weeks. They pupate in thin silk cocoons attached to the stems or undersides of leaves, and in almost 10 days the new adults emerge. Several generations per year.
Cabbage Looper Control
Outbreaks of this pest are not common because they have many natural enemies. Cover plants with floating row cover. Use pheromone traps to determine main flight period for moths, then release trichogramma wasps to destroy eggs. Handpick caterpillars several times a week and spray Safer Garden Dust (Bt-kurstaki) or Monterey Garden Insect Spray (spinosad) as well. Use botanical insecticides, like Tomato & Vegetable Insect Killer or Pyrethrin Spray, only as a last resort. After harvest, bury spent cole crops to destroy cocoons before adults emerge in spring.
Tip: Attract native parasites and predators into your garden by planting flowers for beneficial insects to feed on. These “good bugs” prefer small flowers like those found on parsley, dill, fennel, coriander and alyssum.
Photo Credit: Phil Sloderbeck, Kansas State University