Reduced rates of foliar insecticides for control of Russian wheat aphid (Homoptera: Aphididae) in western Canada

Field and greenhouse experiments were conducted to evaluate reduced rates of foliar insecticides for control of Russian wheat aphid, Diuraphis noxia (Mordvilko), on wheat, Triticum aestivum L. In an initial field experiment on winter wheat, chlorpyrifos at 400 g (AI)/ha was the best treatment, achieving 100% control after 14 d. Subsequent greenhouse experiments indicated that, for chlorpyrifos applied to two-leaf plants using a cabinet sprayer, the rate could be reduced to 100 g (AI)/ha with 91-95% control after 7 d. The toxic action of chlorpyrifos against the aphids was rapid, with 33% control 2 h after spraying. When surviving aphids were removed from treated plants 2 h, 1 d, or 2 d after spraying and incubated on untreated wheat, no further mortality occurred. Apparently, the Russian wheat aphid must receive prolonged exposure to the 0- to 2-d chlorpyrifos residues for adequate ( 90%) control to occur. Chlorpyrifos applied to three-leaf wheat at 125 g (AI)/ha did not provide residual protection against Russian wheat aphid infesting treated plants 2, 4, and 7 d after spraying. Residue analysis showed that chlorpyrifos residues declined rapidly on the treated plants with a half-life of approximately 1 d. Also, by 2 d after spraying, 90% of the residues had been absorbed into the leaves and may not have been available to the infesting aphids. When field applications using a bicycle sprayer were compared directly with cabinet-sprayer applications, better control (93-97% versus 80-83%) was achieved with field applications. In a subsequent aerially applied experiment to field-test reduced rates of chlorpyrifos, 240 g (AI)/ha gave 99% control of Russian wheat aphid on winter wheat after 14 d. We concluded that the recommended rate of chlorpyrifos for control of Russian wheat aphid in western Canada could be reduced from 480 to 240 g (AI)/ha