Differential Mortaiity Response of Lepidopteran Defoliators to Insecticides Deposited within Three Strata of Wide- and Narrow-Row Soybeans

Abstract

Field studies were conducted at two locations within Mississippi to determine the efficacy of aerially applied insecticides within the canopies of wide- and narrow-row soybeans. Water-sensitive cards were placed at three locations within the two canopy types to monitor physical penetration of insecticides in terms of droplets per square centimeter and mean percentage of coverage of the foliage. Estimates of mortality for the soybean looper, Pseudoplusia includens (Walker), in central Mississippi, and for the soybean looper, velvet bean caterpillar, Anticarsia gemmatalis Hubner, and green cloverworm, Plathypena scabra (F.), in south Mississippi were also obtained at three vertical strata. Permethrin (central Mississippi) or methyl parathion (south Mississippi) was applied to both canopies via fixed-wing aircraft and plots were sampled on four postapplication dates. Data suggest that the degree of larva mortality from insecticides differs between row-spacing systems at each vertical stratum. In general, narrow row widths reduced the overall efficacy of an insecticide, but the magnitude of the difference was dependent on the target species. These data are significantly correlated with data on physical penetration of the insecticide, but a great deal of variation is left unexplained. Results of these experiments may assist growers and applicators who have experienced poor control from materials known to be efficacious.