Deposition, distribution, persistence and fate of bacillus thuringiensis variety kurstaki (BTK) in pecan orchards following aerial and ground appucations to control pecan nut casebearer larvae

Abstract Aqueous mixtures of Bacillus thuringiensis Berliner var. kurstaki (Btk) were applied over three plots located in a pecan orchard in New Mexico, USA at a dosage rate of 39.6 billion international units (BIU)/ha and volume rates of 9.4 L/ha (Plot 1), 935 L/ha (Plot 2), and 47 L/ha (Plot 3). Plots 1 and 3 were sprayed aerially using a Cessna 188 aircraft fitted with Micronair AU 5000 atomizers and D8–46 disc‐core (hydraulic) nozzles, respectively. Plot 2 received ground application using a Wilbur‐Ellis air‐blast sprayer. Spray deposit patterns on artificial samplers and live pecan substrates were determined by quantifying the δ‐endotoxin at three different levels in the tree canopy and at ground level using enzyme‐linked immunosorbent assay (ELISA). Droplet density (droplets/cm2) and size spectra were also assessed to evaluate the uniformity of coverage at the three canopy levels using horizontal and cylindrical (vertical) Kromekote card samplers. Droplet density and size spectra on the Kromekote ca...