Loopers
Cabbage Loopers
Description
Adult: The brown-colored moth with a silvery figure eight or “U” shape with a circle beneath on the front wings.
Egg: Eggs are yellowish-white to green, dome-shaped with longitudinal ridges, and laid singly or in groups of six to seven on the upper or lower leaf surfaces.
Larva: The green caterpillars are about 38 mm long at maturity, with a white stripe along each side of the body and several narrow lines along the back. Distinguished by their “loop-like” crawling, where the midsection of their body forms a loop as they bring their back legs (prolegs) toward their front legs.
Pupa: The pupa, about 19 mm long, develops inside a thin white cocoon on the underside of foliage, plant debris, or in soil clods.
Life History
Overwintering as pupae, and adults begin to emerge in late March to April. Most pupae cannot survive the winter in northern Utah due to cold soil temperatures. Moths immigrate from warmer regions in the south. Eggs are laid on the upper and lower leaf surfaces. Larvae feed on foliage for 2 weeks before pupating. The time from egg to adult is about 30 days. There are three to four generations per year in Utah.
Damage
Damage typically occurs after head formation begins in cole crops, but caterpillars can sometimes attack seedling plants. Loopers chew through leaves, creating ragged holes, bore into heads, and contaminate leaves and heads with their bodies and frass (excrement).
Monitoring
- Monitor often. Scout weekly for cabbage loopers by randomly checking one 1 of 10 plants (10%) in small fields, and 1 of 100 plants (1%) in fields > 1 acre. Look on the undersides of leaves for small larvae and eggs. Look for feeding holes; search for larvae nearby and inside damaged heads.
- Use pheromone traps. Mount traps on a stake and place just above crop canopy height at the field edges. Use a pheromone lure specific to cabbage looper to attract male moths to the trap for counting. Moths fly at dusk and into the early nighttime.
Managment
Loopers are difficult to manage once they get inside head-forming cole crop plants. Thus, timely monitoring and management is crucial
Cultural
- Handpick caterpillars. Where practical (in smaller fields), physically remove larvae when plants are young or when only a few loopers are present.
- Use floating row covers. Apply covers before loopers are present to prevent adult moths from laying eggs on plants. Remove covers during flowering to allow for pollination. This option is only practical for home gardens and small commercial fields.
- Plant tolerant varieties. Cabbage varieties with resistance to cabbage looper include ‘Green Winter,’ ‘Savor,’ ‘Savoy Chieftain’, and most red cabbage varieties.
- Sanitation. Clean fields of plant debris after harvest, thus removing overwintering sites for pupae.
- Manage weeds to remove overwintering sites for pupae. Weed hosts for looper caterpillars include wild mustard, pepper grass, and shepherd’s purse.
Chemical
When more than one cabbage looper larva is found in 1 of 10 monitored plants (10%), treat just before heading or at Brussels sprout formation. Seedlings only require treatment if medium- to large-sized caterpillars are present, and defoliation (loss of plant tissue) exceeds 10%.
Biological
Insecticides containing Bacillus thuringiensis var. kurstaki (Bt) and spinosad (e.g., Entrust) are effective in suppressing cabbage looper larvae. Bt must be applied when larvae are still young (< 12 mm long), and plant coverage is important as Bt must be ingested by larvae to be effective.
Alfalfa Loopers
Description
Adult: The wingspan of moths measures 35-45mm. Front wings are gray with various brown patches. There is a prominent silvery white or yellow mark at the center of each forewing. The edge of the front and hind wings have a series of dark spots.
Egg: Eggs are pale yellow, hemispherical, with thin vertical ridges.
Larva: Larvae are green with distinct white stripes along each side and three abdominal prolegs. They develop through five instars growing to 25-35 mm long.
Pupa: Larvae spin a loose, whitish-silk cocoon. Pupae are a black-brown color and 18-20 mm long.
Life History
Alfalfa loopers overwinter as pupae in the soil. Adult moths emerge in late spring and can have up to four generations (a generation lasting 30-40 days) throughout the growing season.
Damage
Larvae initially feed by chewing irregular holes in the foliage. This can eventually skeletonize leaves.
Managment
Cultural
Weedy fields, field borders, and high levels of plant residue provide food sources for alfalfa loopers. Thoroughly till crop residues and control weeds to reduce overwintering looper and feeding sites. Remove cool-season weeds along field edges to starve young caterpillars. Fall tillage can also help destroy or expose overwintering pupae.
Biological
Many predators, parasites, and diseases attack alfalfa loopers. Bacillus thuringiensis (Bt) products can effectively control young larvae.