Integrated Pest Management (I.P.M.) for Cabbage Looper

Cabbage looper (Trichoplusia ni) is a common vegetable garden pest that feeds on many different species of crops, such as: beans, broccoli, cabbage, cauliflower, and other brassica crops. Other host crops include lettuce, parsley, spinach, and tomato.

Identification

Cabbage loopers are about 1- to 1½-inches long. They start life with a dusky white color, and as they eat, they turn pale green. Cabbage loopers have a distinct white stripe down both sides and have a lighter green head; however, the color may vary. More distinctive characteristics for cabbage looper include the following: 2 pairs of abdominal prolegs, fatter on the tail end than the head, and they rear up like a cobra when disturbed. They move by arching their back in a looping motion, thus their name.

Cabbage looper damage typically appears as jagged holes in plant leaves. Female moths lay small hemispherical eggs in clusters of 7 or 8 on the leaves, and these eggs hatch in 1 to 10 days, depending on the temperature.

Cabbage looper damage looks like jagged holes in leaves.
Photo Courtesy of: David Riley, University of Georgia, Bugwood.org

Cabbage looper feeding on a leaf.
Photo Courtesy of: R.J. Reynolds Tobacco Company Slide Set, R.J. Reynolds Tobacco Company, Bugwood.org

Biological Control

The main biological control for caterpillars is Bacillus thuringiensis, also known as B.t. This bacterial spore suspension is best applied as a liquid spray, which is ingested by the insect during feeding. Once inside the caterpillar’s digestive system, the bacterium releases toxins, the caterpillars stop feeding, and then starve to death.

Another effective biological control is from small parasitic wasps. Trichogramma wasps are endoparasitoids, that is, a parasite that lives and reproduces inside another animal and ultimately kills it. They are parasites of the eggs of over 200 species of moths and butterflies and are the most widely released biological control agent in North America. These tiny wasps can be purchased; however, it is far more economical and practical to reduce the usage of harmful broad-spectrum insecticides, so that the naturally occurring wasps visiting the yard are not killed. Many naturally occurring predators and parasites can be attracted to gardens and landscapes by planting a variety of flowering plants for pollen and nectar.

Chemical Control

When biological control measures have failed to keep the population of cabbage loopers under control, a chemical insecticide spray may be needed. The goal with insecticide use is to choose the one with minimal impact to pollinators and natural enemies, but one that is still effective on the insect causing the problem. Before purchasing and using an insecticide, be sure to read and follow ALL label directions. The label is the law; therefore, the product label is the final authority on what crop or areas the product can be applied and at what rate. Always spray late in the day for best results and to better protect beneficial insects.

Insecticidal soaps and oils coat the caterpillar and clog their respiratory system, causing it to suffocate. Soaps and oils are most effective on small caterpillars. These safer use insecticides can also harm beneficial insects upon contact by the spray, but soaps and oils have no residual activity. This means that only beneficial insects and pollinators that were directly sprayed will be affected and not the beneficial insects that arrive after the spray solution has dried. Note that these products can be phytotoxic (damaging to the plant) to drought stressed plants or if applied at temperatures 90 °F or higher. Applications should be made when temperatures are cooler, such as the mid- to late evening, to avoid any potential plant damage. For more information on using insecticidal soaps, see HGIC 2771, Insecticidal Soaps for Garden Pest Control.

Pyrethrin is a botanically derived compound that can be very effective in providing a relatively quick knockdown of caterpillars. These products can harm natural enemies and pollinators that are directly within the spray application, and migrating beneficial insects may be repelled by pyrethrum residue on plant leaves. However, this effect is not long lasting, only a few hours.

Other effective botanically derived chemicals are azadirachtin and neem oil. Azadirachtin is a natural growth regulator that modifies the way insects grow by inhibiting the shedding of their exoskeleton. It also is a feeding deterrent, repellent, and disrupts the mating process and egg laying. Neem oil clogs the spiracles of small-bodied insects, causing them to suffocate. Both chemicals have relatively short residual activity.

The active ingredient spinosad is derived from the Actinomycete bacterium, Saccharopolyspora spinosa. This insecticide provides good control and is less hazardous to pollinators and other beneficial insects, though it is not completely harmless. Caterpillars stop feeding within minutes of being exposed to or ingesting spinosad and usually die within 48 hours. Repeat applications may be necessary as additional eggs hatch.

Malathion is an older, broad-spectrum contact insecticide. Due to its toxicity to pollinators and natural enemies, malathion should only be sprayed on heavily infested plants.

Integrated Pest Management (I.P.M.) Controls for Cabbage Looper

Originally published 01/19