Using Bt for Organic Caterpillar Control in Your Garden
By: Julie Day
If caterpillars are devouring your garden, one safe and effective way to get rid of them is by applying the naturally occurring bacteria known as Bt, or Bacillus thuringiensis. Bt can be applied as a liquid or powder, and many of the varieties are certified organic.
Here’s what you need to know about using Bt to control caterpillars in your garden.
About Bt (Bacillus thuringiensis)
Bt (Bacillus thuringiensis) is a natural bacteria that is commonly found in soil. When eaten by caterpillars, the bacteria produce proteins that paralyze the caterpillar’s digestive system, which causes them to stop feeding and die.
Bt is safe for use in organic gardens because it has a specific target and is nontoxic to humans, animals, and beneficial insects. It’s approved for use in vegetable gardens up to the day of harvest, though all vegetables and herbs should still be thoroughly washed before eaten.
Types of Bt
There are a variety of Bt products available, from powders to baits to liquid concentrates. Different strains of Bt are also available for different purposes, such as:
- Bt (var. tenebrionis/San Diego): This special strain of Bt targets the elm leaf beetle, cottonwood leaf beetle, and potato beetle. It’s sold under names such as Trident, M-One, and Novodor.
How to Apply Bt
The concentrated or wettable forms of regular Bt can be mixed in a small spray bottle or garden sprayer, then carefully applied to the foliage of affected plants. Be sure to follow application instructions for proper dosage and mixing.
When applying Bt:
- Store Bt Properly: Bt products only last a couple of years, with the powdered forms lasting longer than liquids. Store Bt in a cool, dry, shaded place for maximum shelf life.
- Organic Pest Control (video)
- Organic Mosquito Control (video)
- Bacillus thuringiensis (Colorado State University Extension)
- Bacillus thuringiensis (Cornell University Resource Guide)