Susceptibility of Arkansas Palmer amaranth accessions to common herbicide sites of action

Fidel González-Torralva,Vijay K Varanasi,Leonard B Piveta,Jason K Norsworthy,Chad Brabham,Tom Barber

doi:10.1017/wet.2020.56

Fidel González-Torralva, Vijay K Varanasi + Show 4 more

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https://doi.org/10.1017/wet.2020.56

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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

AbstractPalmer amaranth is one of the most difficult-to-control weeds in row crop systems and has evolved resistance to several herbicide sites of action (SOAs). A late-season weed-escape survey had been conducted earlier to determine the distribution of protoporphyrinogen oxidase–inhibitor resistant Palmer Amaranth in Arkansas. The objective of this study was to evaluate the susceptibility of Arkansas Palmer amaranth accessions to commonly used herbicide SOAs. The SOAs evaluated were group 2 + 9, 3, 4, 5, 10, 14, 15, and 27, and the representative herbicide from each group was imazethapyr + glyphosate (79 + 860 g ha−1), trifluralin (1,120 g ha−1), dicamba (280 and 560 g ha−1), atrazine (560 g ha−1), glufosinate (594 g ha−1), fomesafen (395 g ha−1), S-metolachlor (1,064 g ha−1), and tembotrione (92 g ha−1), respectively. Palmer amaranth mortality varied among accessions across SOAs. Averaged across accessions, the mortality rates, by treatment in order from lowest to highest, were as follows: glyphosate + imazethapyr (16%), tembotrione (51%), dicamba at 280 g ha−1 (51%), fomesafen (76%), dicamba at 560 g ha−1 (82%), atrazine (85%), trifluralin (87%), S-metolachlor (96%), and glufosinate (99.5%). This study provides evidence that Palmer amaranth accessions with low susceptibility to glyphosate + imazethapyr, fomesafen, and tembotrione are widespread throughout Arkansas. Of the remaining SOAs, most Palmer amaranth accessions were sensitive; however, within each herbicide SOA, except glufosinate, control of some accessions was less than expected and resistance is suspected.

Highlights

The evolution and spread of herbicide-resistant weeds are partially driven by herbicide use pattern (Kniss 2018)
Most accessions were sensitive to the atrazine rate tested, a few accessions had less than acceptable mortality values and require additional study
On the basis of these results, atrazine remains an effective herbicide on most Palmer amaranth accessions in Arkansas, which is likely a result of corn and grain sorghum [Sorghum bicolor (L.) Moench ssp. bicolor] not being widely grown in the state (USDA 2019)

Summary

Introduction

The evolution and spread of herbicide-resistant weeds are partially driven by herbicide use pattern (Kniss 2018). This can be exemplified by the change in soybean [Glycine max (L.) Merr.] herbicide use patterns in the southern United States for control of herbicide-resistant Palmer amaranth. By 2000, glyphosate (Group 9) became the dominant herbicide used, mainly because of its simplicity and effectiveness in glyphosate-resistant crops and the prevalence of ALS- and MT-resistant Palmer amaranth (Dill et al 2008). Glyphosate-resistant Palmer amaranth was initially confirmed in 2005, and by 2009, most soybean-producing states in the southern United States were infested with glyphosate-resistant accessions (Heap 2020). Protoporphyrinogen oxidase (PPO)-inhibiting herbicides (Group 14) became a common PRE and POST option for Palmer amaranth control (Riar et al 2013), which eventually lead to PPO resistance in Palmer amaranth being confirmed in the mid-southern United States (Copeland et al 2018; Varanasi et al 2018)

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