Fate of avermectin b1a in soil and plants

Abstract

Laboratory studies of the fate of 3H-labeled avermectin B1a (AVM) in Lufkin fine sandy loam, Houston clay, and coarse sand demonstrated that under aerobic conditions the compound was degraded at a fairly rapid rate (respective half-lives of AVM in the three soils at a 1-ppm treatment rate were ca. 14-28, 28-56, and 56 days) to at least 13 radioactive products. The major soil degradation product was an equilibrium mixture (ratio of 1:2.5) of the 8a-hydroxy derivative and the corresponding ring-opened aldehyde derivative of AVM. AVM did not leach in any of the three soil types. In cotton seedlings grown either in aged or unaged samples of Lufkin fine sandy loam treated with [3H] AVM (10 ppm) little (≤0.1 ppm) radioactive material was absorbed by roots and translocated to the aerial portions of the plant. Surface residues of [3H]AVM applied to individual cotton leaves in the field were rapidly depleted (half-life < 1 day) and little radioactive material (maximum of ca. 8%) was absorbed by treated leaves. Field tests of a fire ant bait formulation of [14C]AVM applied to the soil furface at rates of 50, 100, and 500 mg of AI/acre indicated that little if any radioactive material (< 0.01 ppm) was taken up by Bermuda grass grown in the treated areas. © 1984, American Chemical Society. All rights reserved.