Effects of Velvetleaf Competition and Defoliation by Soybean Looper (Lepidoptera: Noctuidae) on Yield of Indeterminate Soybean

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The individual and combined effects of various levels and timing of insectinduced defoliation and velvetleaf (Abutilon theophrasti Medicus) competition on soybean yields were measured during four years of study. Larvae of caged adult soybean loopers, Pseudoplusia includens (Walker), were used to attain planned levels and schedules of defoliation in experimental units consisting of two rows of soybeans 1.8m in length, either weed free or infested with two densities of velvetleaf. Estimates of actual levels of defoliation were recorded from leaflet samples in the first 2 yr of the study, and percentage reduction in leaf area index (LAI) compared to nondefoliated controls was measured in the last 2 yr. Soybean yield was significantly reduced by both defoliation and weed competition, and combinations of defoliation and velvetleaf competition had an additive effect on soybean yield reductions in some plots. Soybean yields were generally lowest in treatments consisting of the highest levels of defoliation and densities of velvetleaf. However, these results showed little, if any, interaction between insect defoliation and velvetleaf competition at the levels included in this study. At soybean growth stage R2, percentage defoliation was a better predictor of yield loss than percentage reduction in LAI, but at R4 the reverse was true.

Document Type: Research Article

Publication date: December 1, 1992

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  • Journal of Economic Entomology is published bimonthly in February, April, June, August, October, and December. The journal publishes articles on the economic significance of insects and is divided into the following sections: apiculture & social insects; arthropods in relation to plant disease; forum; insecticide resistance and resistance management; ecotoxicology; biological and microbial control; ecology and behavior; sampling and biostatistics; household and structural insects; medical entomology; molecular entomology; veterinary entomology; forest entomology; horticultural entomology; field and forage crops, and small grains; stored-product; commodity treatment and quarantine entomology; and plant resistance. In addition to research papers, Journal of Economic Entomology publishes Letters to the Editor, interpretive articles in a Forum section, Short Communications, Rapid Communications, and Book Reviews.
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