Answer: It's probably a cabbageworm or cabbage looper, small green caterpillars that eat leaves. They make a little arch with their body as they move along. If you catch them early, handpicking them is an easy and effective control. Look under leaves and all around the plant. You can often spot their dark, pellet-shaped droppings which can help you locate them. You can also try a forceful spray of water from the hose to knock them off and then round them up in a batch. If they are out of control, you can use Bacillus thurengiensis or Bt. It is a biological control--a bacteria that kills only caterpillars and is safe to other insects, humans and animals. Note however that it will destroy all caterpillars, including the larvae of butterflies.
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