How to Control Caterpillars

Cabbage worms and other leaf-eating caterpillars can quickly decimate a vegetable garden by defoliating plants and even eating fruits, such as tomatoes. If you notice signs of a caterpillar infestation, such as large holes in leaves or fruits, take quick action. Caterpillars are easiest to deal with when they are young and actively feeding. Pesticides are ineffective once the caterpillars stop eating and prepare for the pupae stage.

Floating row covers

Dish soap

Bt

Spinosad

Lay floating row covers over the vegetable garden. These lightweight landscaping fabrics allow sunlight and water to reach plants, but keep insect pests, including caterpillars, out. The covers skim the tops of the plants, allowing for growth. Row covers also insulate plants, protecting them from extreme temperatures. Remove the covers occasionally to pull weeds or harvest vegetables and ensure that no insects have crawled underneath.

Grow crops in a different location every year. Crop rotation is used primarily to minimize soil-borne diseases and prevent soil depletion, but it also works to confuse insect predators in the vegetable garden. Clean up the garden at the end of every season and remove any plant debris. Use mulches judiciously if you have insect pests that might bed or lay eggs in the material.

Hand pick cabbage, tobacco and hornworms in the vegetable garden. Look for these pests on the undersides of leaves. Pull them off and drop them in a bucket of soapy water to dispatch them.

Spray the infested plants with Bacillus thuringiensis, also known as Bt. This natural insecticide is made from bacteria occurring naturally in the soil. It quickly kills caterpillars, but has no effect on humans, animals or bees and other beneficial insects. Spray the plants thoroughly, covering each leaf well. When caterpillars eat the sprayed plants, the bacteria paralyze the gut, causing death by starvation.

Spray Bt during dry weather since it breaks down quickly under wet conditions. This natural pesticide takes several days to kill caterpillars, but the caterpillars stop eating plants almost immediately.

Bt breaks down more quickly than other pesticides and may require a second application. Wait at least one week before making another application. Bt also becomes ineffective with time. Read the package for storage information and discard old products.

Alternate spinosad with Bt to deal with severe infestations. Spinosad is another natural pesticide derived from bacteria. Alternating the two products prevents the caterpillars from developing a resistance to Bt.