SPREAD FACTOR, PENETRATION DEPTH AND STAIN HEIGHT OF DROPS OF AQUEOUSPESTICIDE MIXES ON KROMEKOTE(R) CARDS

Spreading behaviour of water-based pesticide drops ranging from 50 to 450 mum in diameter was studied on Kromekote(R) cards (K-cards), using spray mixes of five chemical insecticides, and three commercial formu lations of Bacillus thuringiensis var. kurstaki (BTK). Spread factors (SF, the ratio of the stain diameter 'D' of a drop on the card to the spherical diameter 'd' of the drop making the stain) ranged from 1.0 t o 4.5. The investigation on the role of drop size on SF, h(P) (the pen etration depth) and h(E) (the stain height), showed that drops of the chemical insecticides underwent complete spreading and penetration int o the card with no h(E) above the card surface, and that both SF and h (P) increased with drop size. The mixes of BTK under-went only partial spreading. The smaller drops (50 to 150 mum) of Dipel(R) 6AF and Thur icide(R) 48LV, were spherical, but the medium ones (150 to 300 mum) pr ovided spherical segments, and the larger drops (300 to 450 mum) forme d flattened cylinders. All BTK drops showed h(E) but not h(P). The dro ps of Foray(R) 48B (50 to 450 mum) formed spherical segments with both h(P) and h(E). The impaction energy of all drops increased dramatical ly with 'd', whereas the SF, h(P) and h(E) increased only gradually. S pread factors of the chemical insecticide mixes increased gradually as the water proportions decreased and the ingredient concentration incr eased. With the most concentrated mix (no water), SF increased dramati cally. All drops of Dipel 6AF and Thuricide 48LV remained spherical, d espite the higher concentration of ingredients; but those of Foray 48B formed spherical segments and showed a decrease in SF at higher conce ntrations. All drops of the BTK mixes took only 30 to 120 min for maxi mum spreading, whereas those of the chemical insecticides (except the most concentrated mixes) took 24 to 48 h. The most concentrated mixes continued to spread until 16 d after impaction, and no increase in SF was noted afterwards. Regardless of the concentration levels, all drop s showed 'finite' SF values, whether they were from chemical or BTK mi xes. Even the most concentrated mixes did not continue to spread indef initely, a finding in contrast to the one observed previously for drop s of non-volatile, oil-based mixes.