Bacillus thuringiensis

Bacillus thuringiensis (Bt--many products) is a selective microbial insecticide formulation using a byproduct of the naturally occurring bacterium Bacillus thuringiensis as its active ingredient. This bacterium is able to exist as a spore until temperature, moisture, and available nutrients are conducive to the reinitiation of the life cycle. Bt exhibits a unique insecticidal activity when eaten by susceptible larvae, specifically those of the insect order Lepidoptera (moths and butterflies).

Bt does not have any of the hazards sometimes associated with chemical insecticides. It has been shown to be incompatible, however, with mixtures with a high pH such as Bordeaux mixtures. In orchards, Bt should provide excellent control of variegated leafroller, tufted apple bud moth, red-banded leafroller, oblique-banded leafroller, green fruitworm, and most forest-orchard species (gypsy moth, tent caterpillar, webworm). If mixing Bt with other products, always add Bt first. Good mechanical agitation is important to quickly mix Bt.