ID

3104-1544

Authors as Published

Eric Day, Department of Entomology, Virginia Tech

Figure 1 cabbage looper
Fig. 1: Cabbage Looper adult and caterpillar

Description

Pale green measuring worm with thin white stripes down back and sides. Up to 1 and 1/2 inches long. Caterpillar doubles-up, or loops, when it crawls.

Common Host Plant(s)

Cabbage, lettuce, cauliflower, kohlrabi, collards, brussels sprouts, turnip, mustard, broccoli and kale.

Damage

Feeds on underside of leaves producing ragged holes; large loopers burrow into heads. Loopers are hard to kill. They become a problem in Virginia in late July or
early August and remain a problem until a killing frost or light freeze occurs.

Distribution

Throughout United States.

Lifecycle

Cabbage loopers overwinter as pupae. In spring cabbage looper moths emerge from their cocoons and mate. Eggs are laid during the night on upper leaf surfaces of brassicae plants. Larvae hatch several days later and feed for about a month on leaves. During this time larvae go through several instars. Mature larvae spin a silk cocoon and pupate. Pupation takes about 13 days if the cabbage looper is not overwintering in the cocoon. Several generations of cabbage loopers can occur during a year with the time from egg to adult only taking a few days over a month.

Figure 2 cabbage loper
Fig. 2: Caterpillar stage of Cabbage Looper. David Cappaert, Michigan State University, Bugwood.org

 

Threshold

Since several pests appear simultaneously on crucifers, all must be considered when applying thresholds. Therefore, the following thresholds take into account the combined levels of the following cole crop caterpillar pests: diamondback moth, imported cabbageworm, cross-striped cabbageworm, and cabbage looper. These thresholds are for fresh market quality cabbage, broccoli, and cauliflower; if more damage is economically acceptable, a 75% infestation may be tolerated before treating plants.

 

Fresh Market Cabbage
 Treatment advised if:
Seedbed10% or more plants infested
Transplant to cupping stage30% or more plants infested
Cupping to early heading20% or more plants infested
Early heading to mature10% or more plants infested

 

Fresh Market Broccoli and Cauliflower
 Treatment advised if:
Seedbed10% or more plants infested
Transplant to first flower50% or more plants infested
Flowering to mature head10% or more plants infested

Cultural Control

Handpick caterpillars off plants. Plow under crop remnants in spring to bury overwintering pupae before the emergence of adults.

Organic/Biological Control

Bacillus thuringiensis, or Bt, (Bactur, Dipel, SOK BT, Thuricide) 2.0 to 3.0 tbsp in 1-gallon water. Bacillus thuringiensis will work but its results are not quickly observable; loopers (and other caterpillars) get sick the first day and die later. It is not necessary to wait before harvesting after an application of Bt.

Several parasitic wasps (Hyposoter, Copidosoma, Trichogramma) attack the cabbage looper as do general predators and virus diseases. Mass releases of Trichogramma may provide control in tomatoes.

Chemical Control

Treat with a registered insecticide every 4 days after first true leaves appear until harvest if worms are still present. Direct insecticide to the undersides of leaves.

References

Foster, Rick and Brian Flood. 1995. Vegetable Insect Management, Meister Publishing Company, Willoughby, Ohio. pp. 104-107.


Virginia Cooperative Extension materials are available for public use, reprint, or citation without further permission, provided the use includes credit to the author and to Virginia Cooperative Extension, Virginia Tech, and Virginia State University.

Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Edwin J. Jones, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; M. Ray McKinnie, Administrator, 1890 Extension Program, Virginia State University, Petersburg.

Publication Date

April 25, 2011

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