Resistance to Glyphosate in Palmer Amaranth (Amaranthus palmeri) Populations from New Mexico Pecan Orchards

Abstract

Two populations of Palmer amaranth suspected of being resistant to glyphosate have been reported since 2007 in pecan orchards in Doña Ana County, New Mexico. The objectives of the study were to confirm and evaluate the level of resistance, to evaluate the effectiveness of alternative herbicide mechanisms of action, and to compare the cost of effective alternative herbicides for weed management in pecan orchards. Greenhouse experiments indicated that the resistant populations were able to survive glyphosate at 736 g ae ha−1. Compared with a susceptible (S) population, one of the resistant (R) populations had sevenfold resistance to glyphosate. POST application of 12 herbicides, with five different mechanisms of action, all provided at least 88% control of both R and S populations when applied at their recommended field rates. PRE application of trifluralin and metolachlor also provided more than 99% control of R and S populations. The results of field studies indicated that the financial benefit of season-long weed management with glyphosate, in pecan orchards, was comparable with some of the tested alternative herbicides.

Glyphosate-Resistant Palmer Amaranth (Amaranthus palmeri) in Nebraska: Confirmation, EPSPS Gene Amplification, and Response to POST Corn and Soybean Herbicides

“…All other treatments resulted in 15% to 80% biomass reduction. Similarly, Mohseni-Moghadam et al (2013b) reported no difference in biomass reduction of two Palmer amaranth biotypes at 16 DAT with glufosinate (>97%) or dicamba (88%) applied POST. Likewise, Jhala et al (2014) reported < 80% biomass reduction of HPPD-and PSIIinhibitor-resistant Palmer amaranth with mesotrione, topramezone, atrazine, halosulfuron-methyl, fluthiacet-methyl, or bromoxynil applied POST at 21 DAT.…”

Glyphosate resistance: state of knowledge

“…Subsequently, a North Carolina GR A. palmeri population was reported with EPSPS gene duplication from 22‐ to 63‐fold . A New Mexico GR A. palmeri population was sevenfold more resistant than a GS population and had EPSPS gene duplication ranging from two‐ to tenfold, and individuals with EPSPS gene duplication were able to survive label‐rate glyphosate applications (0.82 kg ha −1 ) …”

“…57 A New Mexico GR A. palmeri population was sevenfold more resistant than a GS population and had EPSPS gene duplication ranging from two-to tenfold, and individuals with EPSPS gene duplication were able to survive label-rate glyphosate applications (0.82 kg ha −1 ). 58,59 Additional species have recently been reported with EPSPS gene duplication in GR populations, including L. multiflorum, 60 Kochia scoparia, 61 A. tuberculatus 62 and A. spinosus 63 (summarized in Table 1). The reported number of duplicated EPSPS gene copies in K. scoparia and A. tuberculatus populations is lower (from fourto tenfold) than the Georgia, North Carolina and Mississippi 55 -57 A. palmeri populations (Table 1), and similar to the New Mexico A. palmeri population.…”

Inheritance of glyphosate resistance in Lolium perenne and hybrids with Lolium multiflorum

“…In these cases, the target-site mechanism of resistance detected in Eleusine indica and the selective sequestration of glyphosate into vacuoles (non-target site mechanism) observed in C. canadensis would be similarly inherited (Ng et al, 2004b;Ge et al, 2010). On the other hand, the variable number of EPSPS copies explains the different glyphosate sensitivities in resistant A. palmeri and could influence the type of glyphosate resistance inheritance, determining whether it is monogenic or polygenic (Chandi et al, 2012;Mohseni-Moghadam et al, 2013).…”