Effects of Soybean Row Spacing on Spray Penetration and Efficacy of Insecticides Applied with Aerial and Ground Equipment

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Abstract
Kromecote® or water-sensitive cards were placed at three or four vertical levels within the canopy of wide (96.5–101.1 cm) and narrow (17.8–25.4 cm) rows of soybeans, Glycine max (L.) Merrill, to measure spray penetration and droplet characteristics of insecticides applied with aerial or ground equipment. Larval mortality data were used to measure the efficacy of the insecticides at three vertical strata within the two row-spacing systems. The size of the droplets deposited was generally smaller within all levels of the narrow-row canopy compared to the wide-row canopy. The total number of drops per cm2 and mean percentage of coverage was reduced in the narrow-row spacing compared to the wide-row spacing, but only within the median one-third of the canopy. Similarly, the percentage of larval mortality was reduced within the median one-third of the narrow-row plots compared to the wide-row plots at the same level. The variable combination of drops per cm2 and number median diameter was significantly correlated ( R = 0.6535) with the percentage of reductions of lepidopterous larval populations of the soybean looper, Pseudoplusia includens (Walker), velvetbean caterpillar, Anticarsia gemmatalis Hübner, and green cloverworm, Plathypena scabra (Fab.).

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