Influence of weeds on insecticide deposition and soybean looper (Pseudoplusia includens) management

Document Type

Article

Publication Date

1-1-1999

Abstract

Glycine max fields with Sesbania exaltata and Senna obtusifolia were selected to evaluate weed effects on insecticide spray droplet deposition within the crop canopy and soybean looper (Pseudoplusia includens) mortality. Weedy and weed-free treatments with and without thiodicarb insecticide application were included. Soybean looper populations in plots with S. exaltata and S. obtusiolia were approximately half those found in weed-free plots. Thiodicarb reduced soybean looper larval survival in the absence of weeds or when weeds were present in three of four experiments. Dye-sensitive cards placed in the top, middle, and bottom thirds of the G. max canopy showed droplet coverage to be highest on cards placed in the top of the canopy. Weeds reduced insecticide coverage in the top of the G. max canopy 26 to 43%. Thiodicarb deposition within the middle and bottom levels of the canopy was not reduced by weeds. Leaflets from the top, middle, and bottom thirds of the crop canopy were collected immediately after insecticide application to bioassay for insecticide deposition. For both years, mortality of soybean looper larvae on leaflets collected from the middle or top of weedy and weed-free G. max treated with thiodicarb was equivalent. Assuming that an economic return can be expected, soybean looper management may not need to be altered when moderate infestations of S. exaltata and S. obtusifolia are present in G. max in late season.

Publication Source (Journal or Book title)

Weed Science

First Page

321

Last Page

326

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