DROP-SIZE SPECTRA AND DEPOSITS OF 4 BACILLUS-THURINGIENSIS FORMULATIONS ON SIMULATED AND NATURAL FIR FOLIAGE

In aerial spray studies reported in the literature using concentrated aqueous formulations, the segments of drops that remained above the fo liar surface were sized after impaction. The drop volume that could ha ve penetrated into the foliar cuticle was not taken into account. The objectives of the present study were to spray monodispersed drops over natural and simulated balsam fir needles, to determine drop spreading , to measure the sizes of drop segments above the foliage, and to comp ute the drop volume that penetrated into the foliar surface. Four aque ous formulations of Bacillus thuringiensis var. kurstaki, containing a dye and a chemical tracer [triethyl phosphate (TEP)], were sprayed in a laboratory chamber over balsam fir branches clipped from field-grow n trees. Spray was also applied on aluminum fir branches with and with out a coating of the cuticular wax extracted from natural fir foliage. Drop-size spectra, drops/cm2, and deposits (ng TEP/cm2 of foliar area , and ng formulation protein/cm2) were assessed on the natural foliage and wax-coated aluminum foliage (foliar simulator); but only drops/cm 2 and deposits of TEP and protein were measured on the uncoated alumin um foliage. Both natural foliage and foliar simulator received similar drop sizes, drops/cm2, and deposits, but the latter two parameters we re higher on the uncoated aluminum foliage. The investigation provided a new method to determine the actual sizes of drops deposited on a fo liar simulator. The simulator not only had similar size and shape, but also the same surface characteristics. Quantification of protein depo sits was also faster on the simulator than on the natural foliage.