How to Rid Tomato Plants of Inch Worms


Inch worms (also called cabbage loopers, measuring worms or cankerworms) received their name because of the way they inch along, arching their bodies up tree trunks or vegetable stems, according to Cornell University Extension. Normally birds and beetles feed on these 1-inch caterpillars, which vary in color from reddish-brown to green, and parasitic wasps gradually weaken them, keeping the population in check. Inch worms are unlikely to attack tomatoes if their preferred silking ears of corn are nearby.

Step 1

Apply a pesticide to the tomato plants when inch worms are still small, as soon as they appear, in the last three weeks of May in most parts of the country. Both state extension services and organic gardening websites recommend either spinosad (Monterey Garden Insect Spray; Ferti-lome Borer, Bagworm, Leafminer & Tent Caterpillar Spray; and Bulls-Eye Bioinsecticide) or Bacillus thuringiensis or bT (Thuricide). Spinosad and bT are derivative of naturally occurring bacteria and cause the inch worm to stop feeding and die.

Step 2

Alternate between treatments of bT and spinosad so that inch worms do not develop resistance, recommends the Cornell University College of Agriculture and Life Sciences.

Step 3

Shake the pesticide well. Add 2 to 4 tsp. of bT per gallon of water in a three-quarter-filled spray tank after double-checking label directions for application for tomatoes. Apply to thoroughly soak the tomato plant's leaves. Repeat a week after applying spinosad.

Step 4

Add 4 tbsp. of spinosad per gallon of water after double-checking label directions for application for tomatoes, filling the tank and soaking the plant leaves as above. Apply spinosad four to seven days after applying bT, a maximum of four times in a season.

Tips and Warnings

  • Use a trigger, handheld or backpack sprayer. Avoid a hose-end sprayer, which may be less accurate in measuring pesticide and water. Do not use kitchen utensils for measuring; use a separate set of measuring spoons. Do not let mixed pesticide sit in the tank; use immediately.

Things You'll Need

  • Spinosad
  • Bacillus thuringiensis
  • Measuring spoons
  • Tank sprayer


  • Cornell Cooperative Extension: Cankerworms (Inch Worms)
  • NC State University Horticulture Information
  • Planet Natural: Spinosad: An Insecticide To Make Organic Gardeners Smile
  • Cornell University College of Agriculture and Life Sciences: Crop Management Practices
  • Mother Earth News: Organic Remedies for Garden Pests

Who Can Help

  • Online Gardener: Cankerworms
  • Southern Ag: Thuricide HCP
  • Monterey Lawn and Garden Products: Monterey Garden Insect Spray
  • Mother Earth News: Guide to Organic Pest Control
Keywords: inch worms tomatoes, spinosad bT caterpillars, Bacillus thuringiensis, Thuricide

About this Author

Rogue Parrish has written two travel books and edited at the "The Baltimore Sun," "The Washington Post" and the Alaska Newspapers company. She began writing professionally in 1975. Parrish holds a summa cum laude Bachelor of Science degree in journalism from the University of Maryland.