Efficacy and Residues of Foliar Sprays Against the Lettuce Aphid, <i>Nasonovia ribisnigri</i> (Homoptera: Aphididae), on Crisphead Lettuce
Abstract
The systemic insecticides disulfoton. oxydemeton-methyl and demeton, were highly effective in controlling the lettuce aphid, Nasonovia ribisnigri (Mosley) (Homoptera: Aphididae), when sprayed on crisphead lettuce at the early stage of heading. Total residues of disulfoton, applied at 1.12 kg AI/ha and oxydemelOn-methyl at 0.56 kg AI/ha. diminished to less than 0.06 ppm 28 days after application, making these compounds strong candidates to replace the discontinued demeton. The local systemic compounds pirimicarb and methamidophos were intermediate in effectiveness between the systemics listed and contact insecticides such as endosulfan, mevinphos and parathion when applied to lettuce before the heading stage. Seven methods of applying methamidophos at 1. 1 kg AI/ha all provided equally significant levels of lettuce aphid control.
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