Cole crops are susceptible to imported cabbageworm. 

Three different cabbageworms may be found on cabbage, broccoli, Brussels sprouts, collards, kale, kohlrabi, and other cole crops grown in Illinois.

• The imported cabbageworm is a sluggish, velvety-green worm. Adults are white or yellowish-white butterflies with black spots on the wings. 
• The cabbage looper is green with stripes along its back and sides and travels in a looping motion.
• The diamondback moth larva is green and very active.

Habit

In spring, white or brown butterflies may be seen depositing yellow or yellowish-white eggs on the underside of leaves of cabbage and related crops, salad crops, and leafy vegetables. Upon egg hatch, the imported cabbageworm larvae begin feeding on foliage. The adult moths of the other two species lay their eggs at night at about the same time of year.

Damage Caused by Imported Cabbageworms

Cabbageworms attack the heads of cabbages, flowers of broccoli, and curds of cauliflowers. Caterpillars feed on the upper surface of the leaf, creating large, irregular holes. As caterpillars grow, they may move toward the center of the plant leaving only the midribs intact. Defoliation can be severe enough to cause crops to be unsaleable or fit for consumption.

Life Cycle of the Cabbageworm

They first appear in mid-April and they continue to be a problem until mid-September. Adults fly during the day and lay eggs singly on the leaves of cole crops. After feeding, caterpillars will pupate. The bright green pupa is attached to the lower surface of the leaf by a silky thread. Cabbageworms overwinter as pupae in crop debris. The life cycle is about 5 weeks, and 3 to 6 generations can occur in a year.

Management of Imported Cabbageworms

• Removing plant debris and tilling can help manage overwintering cabbageworms.
• Using floating row covers can protect plants and prevent egg laying. Since cole crops don’t need to be pollinated, row covers can be left on plants until harvest.
• Pesticides, such as Bacillus thuringiensis var Kurstaki or Aisawai, can also be used to manage these pests; make sure to read and follow all label directions. 
• Younger, smaller caterpillars are easier to manage than older, larger individuals.

Contact your county Extension office for current pesticide controls.