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

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.

Recent Discovery of Amaranthus palmeri S. Watson in Italy: Characterization of ALS-Resistant Populations and Sensitivity to Alternative Herbicides

“…Due to both economic and environmental factors, post-emergence application of ALS-inhibiting herbicides is the most common weed control strategy in soybean in Italy, and it is likely one of the driving factors of the recent spreading of ALS-resistant amaranths [15]. Several herbicides with alternative sites of action, such as inhibitors of photosystem (PS) I and II, 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase and carotenoid biosynthesis can provide effective control of ALS-resistant populations of A. palmeri [16,17]. However, given the ability of this species to evolve resistance against herbicides with different sites of action [18], the efficacy of potential alternative herbicides should be assessed at local level before recommending their use.…”

Recurrent Selection with Sub-Lethal Doses of Mesotrione Reduces Sensitivity in Amaranthus palmeri

“…This shows that compared to other herbicide SOA, there is a more rapid evolution of sub-lethal dose-mediated mesotrione resistance in A. palmeri . The rapid selection for resistance to HPPD herbicides is not surprising considering the failure of a labeled rate of mesotrione (105 g ai ha −1 ) and tembotrione (92 g ai ha −1 ) to control A. palmeri accessions throughout Arkansas in recent screenings [ 31 , 32 ].…”

“…Under greenhouse conditions, the use of sub-lethal mesotrione rates over several generations selected for resistance in this population was demonstrated. Recent screenings for sensitivity of A. palmeri accessions in Arkansas to mesotrione and tembotrione revealed that a highly variable response was present among sampled sites [ 31 , 32 ]. The evolution of mesotrione resistance under field conditions is possible if reduced herbicide rates are applied for economic reasons, weeds emerge as soil-applied activity of the herbicide partially dissipates, the herbicide is applied to larger weeds than recommended, or environmental conditions are such that they lead to reduced herbicide efficacy [ 35 , 36 , 37 ] because all these scenarios may allow for the selection and accumulation of minor effect resistance conferring alleles in the population.…”

Understanding Resistance Mechanisms to Trifluralin in an Arkansas Palmer Amaranth Population

“…The resistant and susceptible accessions used in this study were documented in earlier experiments described elsewhere [10,27]. In order to characterize the resistance to trifluralin, the resistant accession was further evaluated.…”