How should nets be dried after insecticide treatment in the field?

Different procedures for drying polyamide (nylon) hammock nets (approximately 10 m2) posttreatment were evaluated. Forty-three nets were soaked for 10 min in a plastic bowl containing a solution of water and lambdacyhalothrin 0.05% (target dose of 10 mg/m2). Twenty-two freshly treated nets were put to dry in the sun: 13 of them hung vertically with the roof of the hammock net at the top and the hem at the bottom, and the other 9 were folded and laid flat on a plastic sheet. The rest of the nets (21) were dried in the shade: 11 of them hung vertically and 10 were folded flat on a plastic sheet. After 6-7 h, 2 15-cm2 samples of each net were cut, one on top of the lateral side and one 40 cm from the edge. Concentrations of lambdacyhalothrin were determined by gas chromatography-mass spectrometry on subsamples of netting (1 cm2). The mean insecticide concentrations of samples were compared between nets that were dried in the sun or in the shade, and placed to dry either hanging vertically or folded flat. In general, no differences were found between the mean insecticide concentrations of nets that were dried vertically in the sun or in the shade, or those dried flat in the shade. However, the mean dose was considerably lower in the remaining nets, which were dried flat in the sun. The reason for this is unclear but is hypothesized to be an effect of temperature. Results indicated that nets hung vertically either in the sun or shade dried faster than those laid flat. Based on the time to dry and mean insecticide extracted, it is recommended to hang treated nets vertically in the sun for drying.