Persistence and Efficacy of Bacillus thuringiensis-Based Biopesticide against Chrysodeixis includens in Soybeans: A 3‑Year Field Study

This study aimed to evaluate the persistence of Bacillus thuringiensis (Bt)-based biopesticide and its efficacy against Chrysodeixis includens. The field trials were organized in a factorial design, with three application times (8:00 AM, 12:00 PM, and 6:00 PM) and collection times after application (0, 24, 48, and 72 h). Applications were made using a CO2-pressurized backpack sprayer at 100 L ha–1 at the respective times. Leaves were collected from the upper third of the soybean plants and brought to the laboratory for bioassay preparation, where 48 s-instar larvae per treatment were assessed for mortality. Applications performed in the early morning resulted in higher caterpillar mortality and greater persistence of the active toxin over time. However, pest control decreased as the exposure time of Bt-sprayed leaves to field climatic conditions increased. The control was greatest immediately after application and within the first 24 h, indicating a decline in the residual effectiveness of the product over time.