Development of Bt products is an active area and many manufacturers produce a variety of products. Effectiveness of the various formulations may differ. Development of Bt products is currently an active area and many manufacturers produce a variety of products. Effectiveness of the various formulations may differ. Disadvantages Bt is susceptible to degradation by sunlight.
Most formulations persist on foliage less than a week following application.
Some of the newer strains developed for leaf beetle control become ineffective in about 24 hours. Manufacturers are experimenting with several techniques to increase its persistence. As strictly a stomach poison insecticide, Bt must be eaten to be effective, and application coverage must be thorough. This further limits its usefulness against pests that are susceptible to Bt but rarely have an opportunity to eat it in field use, such as codling moth or corn earworm that tunnel into plants. Since Bt does not kill rapidly, users may incorrectly assume that it is ineffective a day or two after treatment.