Cabbage looper, Trichoplusia ni
Moths are 1.9 cm (0.75 inch) long and have grey or brown bodies. A silver “figure eight” mark in the center of each forewing is a distinguishing feature of this species. Like many moth species, cabbage looper adults are more active at night. Eggs are small, green, and typically laid on leaves. Newly emerged caterpillars are dark white and gradually turn green as they feed voraciously on the undersides of leaves. Mature caterpillars are roughly 3.8 cm (1.5 inches) long with a light green head and green bodies that have wavy white or yellow lines running along the back and sides. Additional morphological features of caterpillars include two pairs of prolegs on the abdomen and a wider tail end of the abdomen. When looper caterpillars move, they raise the middle of their body in a distinct “loop” shape.
- The cabbage looper is a species of moth that can attack a wide range of cabbage and mustard plants including cauliflower, Brussels sprouts, broccoli, cabbage, kale, collard greens, and kohlrabi.
- Larvae are the destructive life stage since they feed on foliage, occasionally causing severe defoliation.
- Mature larvae chew holes in leaf centers and can also bore into the heads of cabbage and broccoli which can stunt plant growth and interfere with head development.
Cabbage looper on a cabbage leaf. The cabbage looper is a species of moth whose caterpillars can attack a wide variety of cabbage and mustard plants. Image credit: Alton N. Sparks, Jr., University of Georgia, Bugwood.org
Cabbage looper visiting a flower. Note the silver figure eight pattern in the center of each forewing. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
A single egg of cabbage looper. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Caterpillar of cabbage looper with body in the “looped” position. These caterpillars form the loop shape as they crawl along surfaces. Image credit: David Cappaert, Bugwood.org
Mature caterpillar feeding on cabbage leaf. Note the large holes caused by feeding of the caterpillar. Image credit: Alton N. Sparks, Jr., University of Georgia, Bugwood.org
Life history and habits
In areas with suitable temperatures cabbage loopers overwinter as pupae. In much of the United States where cabbage looper is present, pupae cannot survive the winter and populations become reestablished the following season when moths migrate north from warmer overwintering sites. A single female moth can lay hundreds of eggs in her lifetime and the timing of egg hatch is highly dependent on temperature. The number of generations depends on location, in warmer climates like California where continuous activity is possible, there can be as many as seven generations each year. In areas that have cooler climates like Canada, cabbage loopers produce two to three generations each year.
Feeding of young larvae causes windowpane patterns on plants with thick leaves such as cabbage. Mature larvae chew ragged holes in the center of leaves and can also bore into the heads of cabbage and broccoli which can stunt plant growth and interfere with head development. Severe infestations can result in defoliation and significant injury.
In head-forming crops, management is extremely challenging once caterpillars bore into the heads. Therefore, timely monitoring and management is very important in preventing significant yield losses. Early in the season, inspect the underside of leaves regularly for eggs, young caterpillars, and signs of feeding injury. Look for ragged holes and mature caterpillars on leaves and in vegetable heads later in the season. Pheromone traps can be placed at canopy height along the field edges. It is important that the traps be baited with a pheromone lure specific to cabbage loopers. The pheromone traps capture male moths where they can be counted.
Some plant varieties are more resistant to looper infestations, and caterpillars can be physically removed from plants by hand picking. This is more practical in smaller fields when plants are young or when caterpillar densities are low. Floating row covers can provide a physical barrier that protects plants from egg laying moths. Covers should be removed during flowering so pollinators can forage. While effective, this method is only practical for home gardens and small growing operations. After harvest, remaining plant debris should be removed from fields to reduce the space available for overwintering pupae. Weed hosts such as wild mustard, pepper grass, and shepherd’s purse should also be removed.
There are a couple of naturally occurring enemies that can be used in cabbage looper management. Most notably the bacteria Bacillus thuringiensis and different Trichogramma spp., which are parasitoid wasps that commonly attack the eggs of over 200 species of moths and butterflies. Both natural enemies are commercially available. In the case of wasps, limiting the use of broad-spectrum insecticides will help preserve naturally occurring species. The inclusion of flowering plants in gardens will attract these nectar-feeding wasps to the area and may provide nearby vegetables with additional protection against the cabbage looper.
Insecticides should be applied before heading or Brussels sprout formation. Good control often requires several applications, and it is recommended that growers rotate insecticides with different toxins to prevent resistance from developing in the looper population. Consult the Utah State University factsheet for more information on chemical control of the cabbage looper.
University of Maryland. 2022. Cabbage Looper on Vegetables. University of Maryland -Extension. Available https://extension.umd.edu/resource/cabbage-looper-vegetables
Jeffers, A. 2019. Integrated Pest Management (I.P.M.) for Cabbage Looper. Clemson Extension – Home & Garden Information Center. Available https://hgic.clemson.edu/factsheet/integrated-pest-management-i-p-m-for-cabbage-looper/
University of Massachusetts Amherst. 2013. Cabbage Looper. UMass Extension – Center for Agriculture, Food, and the Environment. Available https://ag.umass.edu/vegetable/fact-sheets/cabbage-looper
Eaton, A. 2016. Cabbage Looper: Pest Fact Sheet 11. University of New Hampshire – Extension Available https://extension.unh.edu/resource/cabbage-looper-fact-sheet
Utah State University (n.d.). Cabbage Looper. Utah State University – Extension. Available https://extension.usu.edu/vegetableguide/brassica/cabbage-looper