Development and Testing of a Preventive Program for Control of the Alfalfa Weevil in Ohio1

Abstract

In 1967, eight insecticides or combinations of insecticides were field tested for effectiveness against adult Hypera postica (Gyllenhal). Methyl parathion was the most effective insecticide tested, followed by a combination of malathion + methoxychlor, and azinphosmethyl. Preliminary field tests led to the development of a preventive program designed to control the alfalfa weevil with 2 sprays of methyl parathion timed to keep the adult population level low and thereby to suppress opposition. In southern Ohio the 1st spray was applied when the 1st small larvae could be found in the alfalfa terminals. In the northern half of Ohio the 1st application was made according to designated dates ranging from April 15 to April 20. The 2nd spray in all areas was applied 25–30 days after the 1st. In 1968 the preventive program was tested in 20 countries on 41 alfalfa fields (842 acres). The results showed excellent control through the 1st week of June and good control through mid-June. Preliminary tests showed that control of the alfalfa weevil with fall applications of nonresidual pesticides, such as methyl parathion, was not possible. because movements of the adult population during February, March, and April led to repopulation of treated fields. Repopulation was also noted 20-30 days after sprays were applied in April. Tests showed that unless a second application was made to control these adults, damaging populations of larvae developed.