Field Insecticide Tests for Alfalfa Weevil and Pea Aphid

Abstract

Seven insecticides, including two new systemics, were tested against the alfalfa weevil, Hypera poslica (Gyll.), and the pea aphid, Macrosiphum pisi (Harris), in randomized, replicated field plots. Materials used and rates of application are included. April 30 was the spray date. Results were obtained by sampling insects with an insect net, May 9, 16, and 29, The percentage of control, or reduction of infestation, was obtained for each material for each date. The new systemics, American Cyanamid Company Compound 12880 ( O,O -dimethyl- S -(N-methylocarbamoylmethyl) phosphorodithioate) and Compound 18706 ( O,O -dimethyl- S -(N-ethylcarbamoylmethyl) phosphorodithioate), showed promising results against the pea aphid (97% reduction in numbers 16 days after treatment). These chemicals gave a quick reduction of alfalfa weevil adults (98% and 96% control at the 9-day sampling), and Compound 12880 substantially reduced the weevil larvae for the same period. All materials except Compound 18706 produced some chlorosis in the alfalfa; however, Compound 12880 produced only a negligible amount. Guthion® ( O,O -dimethyl S -( 4-oxo-3 H -1, 2,3,-benzotriazine-3-methyl) phosphorodithioate) performed well against both pea aphid (89% control at the 16-day sampling) and the alfalfa weevil, at 9 days. None of the test materials at the dosages used appeared ns effective against alfalfa weevil as heptachlor combined with malathion.