Cabbage Looper

Host Plants

The cabbage looper feeds on a wide array of vegetable plants, including cabbage, broccoli, cauliflower, brussels sprouts, collards, kale, mustard, radish, rutabaga, turnip, and watercress. Other crops subject to their influence include celery, beet, cucumber, lima bean, lettuce, etc.

Regions impacted

Common throughout most of the United States and southern regions of Canada.

Description

• The adult cabbage looper is a mottled grayish-brown moth with a 1½ inch wing span. It features a distinctive silvery-white figure 8 or “U” in the middle of each of the front wings.
• The moths are nocturnal but can be seen during the day resting on the underside of foliage.
• The larva is a smooth, greenish caterpillar with two white stripes on each side. Young larvae are about 1/8 to 1/4″ in length; mature larvae grow to over 1½” in length. They have three pairs of slender legs near the head and three pairs at the hind end. There are no legs in the middle section, which is generally humped up when the insect is moving. The cabbage looper can be confused with the cabbage worm, but the distinctive manner in which it hunches itself up in an arched or looped shape to move forward is a key distinguishing characteristic.
• Larvae form pupae or cocoons later in their lifecycle; they are light green when young and gradually turn dark brown when mature. They are about three-fourths of an inch long and wrapped in a delicate cocoon of white threads. Pupae are usually found on the underside of lower leaves.
• Cabbage looper eggs are light green in color and dome-shaped, with the flat side glued to the undersides of the leaves. At about the size of a pin-head, they are deposited singly or in clusters of six to eight eggs.

Life Cycle

• Cabbage looper moths emerge from overwintering pupae or cocoons in mid-spring and are active at night, mating and feeding.
• Each female can lay between 300-600 eggs within the 10-12 day adult lifespan. The cabbage looper eggs hatch in 3-10 days.
• Over the 3-4 week larval stage, they change color and molt as they grow and mature. They consume a significant amount of the host’s foliage during this period, doing the most damage.
• They then form a pupa or cocoon and will either emerge 4-12 days later or overwinter if later in the season and in warmer regions.
• Although capable of spending considerable time as a pupa, they do not tolerate prolonged cold weather.
• The cabbage looper reinvades most of the United States and all of Canada annually after overwintering in southern latitudes.
• There are 3 to 5 generations per year, dependent upon climate.

Damage and Detection

• Young larvae feed between veins on the underside of the lower leaves of cabbage family plants and many other vegetable crops.
• More mature larvae make ragged holes in the foliage and move to the center of the plant.
• Large loopers can also burrow directly into the developing cabbage head. Plants can be severely defoliated and stunted, producing no heads or becoming unfit for marketing or consumption.
• A bonus is the large accumulations of sticky, wet fecal material on and around the plants – larvae consume three times their body weight daily…
• Although serious infestations can cause plant and crop loss, the larvae are not as destructive as one would think, given harvesting of the cabbage usually entails the stripping of the outer leaves where most of the damage occurs.

Prevention and Control

Manual Removal

• When plants are young, or only a few larvae are present, handpick the larvae and egg masses.

Use row covers

• Before plants become infested in the spring, cover the plants with light row coverings to prevent adult moths from laying eggs on the plants.

Plant tolerant varieties

• The green cabbage varieties, ‘Green Winter’, ‘Savoy’’, and ‘Savoy Chieftain’, all exhibit some resistance to attack by cabbage looper. The red cabbage varieties are generally less preferred by cabbage loopers.

Fall sanitation

• Clean up and dispose of all plant debris after harvest to remove the overwintering pupae of the insect.

Control weeds

• Since the caterpillars can overwinter on weeds, remove weeds such as wild mustard and pepper grass which can harbor the pest.

Beneficial insects and predators

• Parasitic wasps (which do not sting) lay their eggs inside or on top of the cabbage looper and their pupae. Once their eggs hatch, the wasp larvae feed on the host caterpillar, killing it.
• These beneficial insects are available by mail order from various providers.

Use insecticidal soap or Bt spray

• Caterpillars can be controlled with the use of insecticidal soap or Bacillus thuringiensis (Bt), a bacteria which causes the caterpillars to become sick and die. Small loopers are more easily controlled with Bt than larger ones.