Microbial Pesticides

Formulation Ingredients Can Increase Residual Activity of Bt

Microbial pesticides based on Bacillus thuringiensis have a short residual activity when applied as foliar sprays. Are there any ingredients that can be added to improve the length of activity in the field?

Pregelatinized cornstarch and corn flour were used as formulation ingredients for sprayable B. thuringiensis preparations in two field tests. Pregelatinized starch mixed with equal amounts of sucrose and tank mixed at a total of 4% solids provided protection of B. thuringiensis on cabbage leaves for up to 5 days under sunny field conditions, while a commercial B. thuringiensis product lost activity after 3 days. Pregelatinized flour mixed with sucrose also provided protection in the presence of rainfall at 4% solids. Inclusion of sun screening agents did not affect activity overall efficacy of all B. thuringiensis preparations against three Lepidoptera species was excellent.

In laboratory tests with artificial sunlight, those formulations containing only 0.5% solids protected equally well as formulations with 4% solids. However, in artificial rainfall tests, all formulations were washed equally from cotton plants when exposed to heavy rain (2-1/2 inches applied over a l hour period).

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