Spread factor, penetration depth and stain height of drops of aqueous pesticide mixes on kromekote^® cards

Abstract

Spreading behaviour of water‐based pesticide drops ranging from 50 to 450 μm in diameter was studied on Kromekote^® cards (K‐cards), using spray mixes of five chemical insecticides, and three commercial formulations 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 to 4.5. The investigation on the role of drop size on SF, h_p (the penetration depth) and h_E (the stain height), showed that drops of the chemical insecticides underwent complete spreading and penetration into 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 underwent only partial spreading. The smaller drops (50 to 150 μm) of Dipel^® 6AF and Thuricide^® 48LV, were spherical, but the medium, ones (150 to 300 μm) provided spherical segments, and the larger drops (300 to 450 μm) formed flattened cylinders. All BTK drops showed h_E but not h_p. The drops of Foray^® 48B (50 to 450 μm) formed spherical segments with both hp and h_E. The impaction energy of all drops increased dramatically with ‘d’ whereas the SF, h_p and h_E increased only gradually.

Spread factors of the chemical insecticide mixes increased gradually as the water proportions decreased and the ingredient concentration increased. With the most concentrated mix (no water), SF increased dramatically. All drops of Dipel 6AF and Thuricide 48LV remained spherical, despite the higher concentration of ingredients; but those of Foray 48B formed spherical segments and showed a decrease in SF at higher concentrations.

All drops of the BTK mixes took only 30 to 120 min for maximum 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 drops showed ‘finite’ SF values, whether they were from chemical or BTK mixes. Even the most concentrated mixes did not continue to spread indefinitely, a finding in contrast to the one observed previously for drops of non‐volatile, oil‐based mixes.

Key words:

• Spread factor
• drop penetration
• impaction energy
• aqueous spray mix
• fenitrothion
• aminocarb
• permethrin
• mexacarbate
• diflubenzuron
• Bacillus thuringiensis var. kurstaki

Notes

Visiting Scientist, Permanent address: Institute of Plant Protection, Shanxi Academy of Agricultural Sciences, 6 Nongke Road, Taiyuan, P.R. China.