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26 May 2020 Susceptibility of Arkansas Palmer amaranth accessions to common herbicide sites of action
Fidel González-Torralva, Jason K. Norsworthy, Leonard B. Piveta, Vijay K. Varanasi, Tom Barber, Chad Brabham
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Abstract

Palmer 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.

© Weed Science Society of America, 2020. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
Fidel González-Torralva, Jason K. Norsworthy, Leonard B. Piveta, Vijay K. Varanasi, Tom Barber, and Chad Brabham "Susceptibility of Arkansas Palmer amaranth accessions to common herbicide sites of action," Weed Technology 34(5), 770-775, (26 May 2020). https://doi.org/10.1017/wet.2020.56
Received: 13 February 2020; Accepted: 15 May 2020; Published: 26 May 2020
KEYWORDS
Herbicide resistance
herbicide screening
Multiple herbicide resistance
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