DIFFERENCES IN PENETRATION AND EFFICACY OF INSECTICIDE SPRAYS APPLIED BY AERIAL AND GROUND EQUIPMENT TO SOYBEAN1

Abstract

Insecticide sprays were applied to conventionally spaced (76.2 cm) soybean, Glycine max (L.) Merrill, by aerial and ground equipment. Drop penetration (no. drops/cm2 and mean percent coverage) and drop size (number median diameter) were measured within and between the two treatments. Larval mortality was determined at each of three vertical strata of the canopy for the soybean looper, Pseudoplusia includens (Walker), in central Mississippi and for a pest complex of the soybean looper, green cloverworm, Plathypena scabra (F.), and velvetbean caterpillar, Anticarsia gemmatalis Hubner, in south Mississippi. At both locations aerial equipment deposited a drop size in successively decreasing numbers/unit area from the top down within the upper two-thirds of the canopy. Conversely, ground equipment generally delivered successively smaller and fewer drops to each lower level within the canopy at both locations. Significantly more spray droplets were deposited at each sample location in the soybean canopy by ground equipment than by aerial equipment. Mortality data indicated that permethrin (0.11 kg AI/ha) provided better control of the soybean looper when applied with ground equipment than with aerial equipment in central Mississippi, while methyl parathion (0.28 kg Al/ha) was equally effective when applied by air or ground in south Mississippi for control of the pest complex. Largest mortality was observed within the upper one-third of the soybean canopy for both methods of application at the two locations.