Identification

• Adult cabbage whites are medium-sized white butterflies with dark gray tips and spots on their forewings. Females deposit single, off-white eggs on the undersides of plant leaves. Eggs have vertical ridges. The caterpillars that emerge are small but, as they feed, grow to measure about 1 1/4 inches in length. Caterpillars are pale green with a velvety texture. A single, narrow yellow stripe runs down the length of their bodies.
  
  

Damage

• Imported cabbageworms eat large, irregular holes in the leaves of cabbage and related crops. You frequently will find them out of sight, on the undersides of leaves. They can enter the head of the cabbage plant or damage the flowers on broccoli and cauliflower, causing considerable damage that can render a crop inedible. Cabbage heads often rot from within due to feeding activity from the imported cabbageworm.
  
  

Control

• If you have only a few plants in the home garden, you can control the imported cabbageworm by handpicking the caterpillars as you find them. Because the caterpillars blend with the leaves, look for piles of the caterpillar's dark green feces. For larger plantings or more serious infestations, both organic and chemical insecticides can control the imported cabbageworm.
  
  Bacillus thuringiensis, or Bt, is a natural control of the imported cabbageworm. This insecticide causes a disease in the cabbageworm while posing little risk to other insects in the garden. Because Bt poses no threat to people, you can use it right until harvest. Stronger insecticides -- both organic and conventional -- also are available. Follow instructions on the label and focus on spraying the underside of leaves where eggs and caterpillars tend to be present.
  
  

Prevention

• Cabbage white butterflies need access to plants in order to lay eggs, so some gardeners control this pest by simply covering susceptible plants with floating row covers. Plants become especially susceptible to damage beginning in July, as cabbage white butterfly populations rise. Planting cabbage and related crops earlier often allows you to avoid the worst damage. After harvesting your vegetables, thoroughly clean the garden of debris , especially if you've had an imported cabbageworm infestation.