Cabbage looper, Tricholplusia ni (Hübner), and bollworms, Heliothis zea. (Boddie), were used to evaluate performance specifications for conventional formulations of Bacillus thuringiensis var. kurstaki and Baculovirus heliothis, respectively. Correlation coefficients between mortality and application rate (amount technical material per ha), droplet size, density (number of droplets per cm2) or concentration indicated that application rate was more important than droplet size, density, or concentration. Several combinations of droplet size, density, and concentration provided effective insect mortality.
A TX-1, hollow-cone nozzle operated at 552-kPa (1 kPa = 6.9 psi) pressure produced significantly larger volumetric and density deposits than did larger nozzles operating at lower pressures when the volumetric application rates were equal. The TX-1 nozzle, however, was significantly inferior to larger nozzles operating at lower pressures when results were based on larvae mortality of cabbage loopers.
Spray deposits (volumetric and density) and larval mortality decreased in sequential samples taken from the top to bottom of soybean plants. One formulation designated HPC usually deposited more volume and droplets per cm2 than did the 16B formulation.
Serial dilution-type bioassay tests indicated that neither high pressure or high shear was detrimental to the activity of crystals of B. thuringiensis. Scanning electron microscope analyses showed a crystal loss from droplets sprayed at an increased pressure.
