Impact of postemergence herbicides on soybean injury and canopy formation

Grant L Priess,Jason K Norsworthy,Trenton L Roberts,Edward E Gbur

doi:10.1017/wet.2020.55

Grant L Priess, Jason K Norsworthy + Show 2 more

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https://doi.org/10.1017/wet.2020.55

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Journal: Weed Technology	Publication Date: May 26, 2020
Citations: 6	License type: CC BY 4.0

Affiliation: University of Arkansas at Fayetteville

Abstract

AbstractField studies were conducted in 2017 and 2018 in Arkansas to evaluate the injury caused by herbicides on soybean canopy formation and yield. Fomesafen, acifluorfen, S-metolachlor + fomesafen, and S-metolachlor + fomesafen + chlorimuron alone and in combination with glufosinate were applied to glufosinate-resistant soybean at the V2 growth stage. Soybean injury resulting from these labeled herbicide treatments ranged from 9% to 25% at 2 wk after application. This level of injury resulted in a 4-, 5-, 6-, and 6-d delay in soybean reaching 80% groundcover following fomesafen, acifluorfen, S-metolachlor + fomesafen, and S-metolachlor + fomesafen + chlorimuron, respectively. There was a 2-d delay in soybean reaching a canopy volume of 15,000 cm3 following each of the four herbicide treatments. The addition of glufosinate to the herbicide applications resulted in longer delays in canopy formation with every herbicide treatment except glufosinate + fomesafen. Fomesafen, acifluorfen, S-metolachlor + fomesafen, and S-metolachlor + fomesafen + chlorimuron, each applied with glufosinate, delayed soybean from reaching 80% groundcover by 2, 7, 8, and 9 d, respectively, and delayed the number of days for soybean to reach a canopy volume of 15,000 cm3 by 2, 3, 2, and 2 d, respectively. No yield loss occurred with any herbicide application. A delay in percent groundcover in soybean allows sunlight to reach the soil surface for longer periods throughout the growing season, possibly promoting late-season weed germination and the need for an additional POST herbicide application.

Highlights

Protoporphyrinogen oxidase-(PPO) and acetolactate synthase-(ALS) inhibiting herbicides historically have successfully controlled Amaranthus spp. (Harris et al 1991; Mavo et al 1995)
Beyers et al (2002) found that PPO- and ALS-inhibiting herbicides mixed with glufosinate resulted in up to 21% injury to glufosinate-resistant soybean; those findings are comparable to injury levels observed in experiments that we conducted
Soybean injury caused by PPO-inhibiting and ALS-inhibiting herbicides alone and in combination with glufosinate can result in a delay in soybean canopy formation

Summary

Introduction

Protoporphyrinogen oxidase-(PPO) and acetolactate synthase-(ALS) inhibiting herbicides historically have successfully controlled Amaranthus spp. (Harris et al 1991; Mavo et al 1995). PPO-inhibiting herbicides were widely used to control Amaranthus species before the release of glyphosate-resistant crops (Norsworthy et al 2012). PPO-inhibiting herbicide use increased substantially following widespread resistance of Amaranthus species to ALS and glyphosate (Norsworthy et al 2008). Palmer amaranth resistant to PPO-inhibiting herbicides was subsequently documented in Arkansas in 2015 (Salas et al 2016). Herbicides that inhibit PPO and ALS are less effective today because of the evolution and spread of PPO- and ALS-resistant Palmer amaranth and common waterhemp (Salas et al 2016; Varanasi et al 2018)

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