Persistence of bacillus thuringiensis deposits in oak foliage, after aerial application of foray® 48b using rotary and pressure atomizers

Abstract A commercial formulation of Bacillus thuringiensis var. kurstaki (Btk), Foray® 48B, was sprayed aerially over blocks selected in a hardwood forest in the USA at the rate of 90 billion international units in 7.0 L/ha, using a helicopter and a fixed‐wing aircraft, each fitted with pressure or rotary cage atomizers. Droplet size spectra were assessed on foliage using two new parameters, viz., droplet‐spot number median diameter (S‐DN.5) and protein mass median diameter (S‐DM.5). The data indicated that when rotary cage atomizers were used, the droplet spectra were narrow with smaller S‐DN.5 and S‐DM.5 values, than when pressure atomizers were used. The protein mass deposits corresponded with the droplet sizes, i.e., the larger the droplet sizes, the greater the deposits. The initial bioactivity did not correspond with the deposits, because the greater the deposits the lower the activity. Persistence of bioactivity also showed irregularities, indicating the role of environmental transformation of for...