Relative Tolerance of Peanuts to Alachlor and Metolachlor1

Abstract Field studies were conducted during 1984, 1985, and 1987 to evaluate weed control and the relative tolerance of peanuts (Arachis hypogaea) to alachlor and metolachlor when applied at rates from 2.2 to 13.4 kg ai/ha. Both single and split preemergence, and postemergence applications were included. In 1984 and 1985, neither herbicide adversely affected yields compared to a hand-weeded control. In 1987, metolachlor at a rate of 9.0 kg/ha and alachlor at 13.4 kg/ha reduced yields. Across all years, at least a two-fold safety factor existed between the maximum registered rate and the rate necessary for peanut injury. Occurrence of injury appears to be related to rainfall. Metolachlor was slightly more mobile than alachlor in soil chromatography trials, which may be a factor in its slightly greater propensity to be injurious under certain conditions of extensive leaching and/or slow peanut emergence.