LEAF RESIDUE COMPARTMENTALIZATION AND EFFICACY OF PERMETHRIN APPLIED TO SOYBEAN

Abstract

Permethrin (EC, 0.084 kg AI/ha) was applied to soybean by backpack sprayer and eight determinations of leaf residue compartmentalization and insect mortality were made during the 27 days following application. After 6 days, 40% of the initial surface permethrin residue remained; after 27 days, 8% of the initial residue was left. Below-surface residues almost tripled in the first 4 days after application and then remained at about the same level thereafter. The surface residues disappeared with a half life of 7.7 days, whereas total leaf permethrin content persisted with a half life of 13.9 days. The observed insect control correlated with the known feeding habits of the insects. Velvetbean caterpillar, Anticarsia gemmatalis Hübner, which by feeding on foliage is exposed to total leaf insecticide content, was controlled for the entire investigation. Threecornered alfalfa hopper, Spissistilus festinus (Say), which feeds on petioles and peduncles, was controlled for at least the first 4 days after application. The number of southern green, Nezara viridula (L.), and green, Acrosternum hilare (Say), stink bugs, which feed on pods, also stayed below the check for at least 4 days after treatment. Thus the leaf permethrin content appeared to be available for effective control of threecornered alfalfa hopper and the stink bugs for ca. 0.5 half life of the residues on the surface, even though after this time surface residues were still measurable.