Efficacy of residual herbicides influenced by cover-crop residue for control of Amaranthus palmeri and A. tuberculatus in soybean

Clay M Perkins,Bryan G Young,Karla L Gage,Aaron Hager,Mandy D Bish,Jason K Norsworthy,Lawrence E Steckel,Kevin W Bradley

doi:10.1017/wet.2020.77

Abstract

AbstractField studies were conducted in 2018 and 2019 in Arkansas, Indiana, Illinois, Missouri, and Tennessee to determine if cover-crop residue interfered with herbicides that provide residual control of Palmer amaranth and waterhemp in no-till soybean. The experiments were established in the fall with planting of cover crops (cereal rye + hairy vetch). Herbicide treatments consisted of a nontreated or no residual, acetochlor, dimethenamid-P, flumioxazin, pyroxasulfone + flumioxazin, pendimethalin, metribuzin, pyroxasulfone, and S-metolachlor. Palmer amaranth took 18 d and waterhemp took 24 d in the cover crop–alone (nontreated) treatment to reach a height of 10 cm. Compared with this treatment, all herbicides except metribuzin increased the number of days until 10-cm Palmer amaranth was present. Flumioxazin applied alone or in a mixture with pyroxasulfone were the best at delaying Palmer amaranth growing to a height of 10 cm (35 d and 33 d, respectively). The herbicides that resulted in the lowest Palmer amaranth density (1.5 to 4 times less) integrated with a cover crop were pyroxasulfone + flumioxazin, flumioxazin, pyroxasulfone, and acetochlor. Those four herbicide treatments also delayed Palmer amaranth emergence for the longest period (27 to 34 d). Waterhemp density was 7 to 14 times less with acetochlor than all the other herbicides present. Yield differences were observed for locations with waterhemp. This research supports previous research indicating that utilizing soil-residual herbicides along with cover crops improves control of Palmer amaranth and/or waterhemp.

Highlights

Winter-annual cover crops have become more readily used as a soil conservation practice across the United States
Palmer amaranth took 18 d in the cover crop–alone treatment to reach a height of 10 cm
All herbicides except metribuzin increased the number of days until 10-cm tall Palmer amaranth plants were present (Table 3), and the increase ranged from 7 to 17 d

Summary

Introduction

When Palmer amaranth and waterhemp emerged at a density of 8 weeds m−2, soybean yield was reduced 78% and 56%, respectively (Bensch et al 2003). Density of Amaranthus spp. was estimated by counting the number of Palmer amaranth and waterhemp plants from two 1-m2 quadrants recorded at each of the following evaluation timings: 14, 21, 28, 35 d. Palmer amaranth took 18 d in the cover crop–alone (nontreated) treatment to reach a height of 10 cm (data not shown).

Results

Conclusion