The persistence of insecticide spray deposits on woven polypropylene and jute sacking

Abstract

Abstract In a trial, simulating the spray treatment of bags, the persistence and biological activity of insecticide spray deposits on jute and woven polypropylene sheets have been compared; in addition, the build‐up of residues in thin layers of maize under the sprayed sheets has been measured. The insecticides were found to have a much shorter persistence on polypropylene than on jute and this was coupled with higher residues on the grain. However, the deposits on polypropylene retained equal or greater activity against Sitophilus zeamais Motsch. and Tribolium castaneum (Herbst) than the deposits on jute, despite the loss of surface deposit. Wettable powder formulations had a slightly greater surface persistence than emulsifiable concentrates and resulted in smaller residues in the grain. There would seem to be more usefulness in using insecticide sprays on woven polypropylene than on jute bags, and a wettable powder formulation of a non‐volatile insecticide of low mammalian toxicity would be the best choice. Of the insecticides tested, the pyrethroid permethrin ( cis: trans ratio= 25:75) was the most effective and gave the least residue in the grain.