Bt (Bacillus thuringiensis) (Agree, Biobit, Condor, Crymax, Dipel, Javelin, MVP, Thuricide, XenTari)

Bacillus thuringiensis (Bt) are aerobic, spore-forming, rod-shaped bacteria that form crystals of protein called delta-exotoxins. Several different types of exotoxins are produced by two B. thuringiensis subspecies and their various strains which, when ingested, damage the stomach wall of Lepidoptera larvae. These types of exotoxins are produced in varying proportions by the different strains and are formulated for use in tree fruits. B. thuringiensis subsp. aizawai products include Agree and XenTari. B. thuringiensis subsp. kurstaki products include Biobit, Condor, Crymax, Dipel, Javelin, MVP, and Thuricide. MVP is unique in that it consists of delta-exotoxins encapsulated in killed Pseudomonas fluorescens to extend field efficacy.

Bts in general provide control of larvae of tufted apple bud moth (TABM), other leafrollers, green fruitworm, and most forest-orchard species (gypsy moth, tent caterpillars, webworms) that feed on foliage. Control of Oriental fruit moth and codling moth larvae is less successful because these larvae feed internally and may not ingest enough toxin. MVP has been shown to be less effective on TABM than other Bt products. Although Bts are generally safe for applicators and to most nontarget species, XenTari is highly toxic to honey bees and other natural enemies exposed to direct spray.

Since Bts are effective only against larvae and not eggs, they should be applied beginning about one week later, when 20 percent of the eggs have hatched. Extenders that block ultraviolet degradation may improve the efficacy of Bts. If mixing Bts with other products, always add the Bt first and use good mechanical agitation. Bts are incompatible with mixtures having a high pH. Thorough spray coverage is needed to provide a uniform deposit of Bts insecticide at the site of larval feeding.