Response of Northeastern Arkansas Palmer Amaranth (Amaranthus Palmeri) Accessions to Glyphosate

Abstract

Palmer amaranth accessions were collected from 21 fields in northeastern Arkansas in the fall of 2006 to determine if they differed in response to increasing doses of glyphosate and to determine the survival frequency following treatment with the label rate (870 g ae/ha). The herbicide dose required to kill 50% of individuals in an accession (LD50) ranged from 41 to 339 g/ha glyphosate, with most accessions responding similarly to glyphosate. The AR18 and AR19 were the least-sensitive accessions, with LD50rates of 312 and 339 g/ha glyphosate, respectively. The mean survival frequency was 2.2% across all accessions when 870 g/ha glyphosate was applied to five- to seven-leaf plants. Sixteen of the accessions had at least one plant survive glyphosate at 870 g/ha. AR18 and AR19 accessions had a survival frequency of 6.3 and 11.8%, respectively. Following an additional cycle of selection with glyphosate, 44.3% of the progeny from the AR19 accession survived glyphosate at 870 g/ha, and its LD50value significantly increased to 646 g/ha glyphosate. This research shows that there is a low percentage of Palmer amaranth plants currently present in production fields throughout northeastern Arkansas that are capable of surviving a single glyphosate application at the labeled rate and that further selection with glyphosate can increase the frequency of survival.

Distribution of glyphosate‐resistant Amaranthus spp. in Nebraska

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Herbicide‐resistant weed management: focus on glyphosate

“…The advent of GR crops reduced diversification in alternative herbicide usage owing to glyphosate's broad spectrum of weed control. On the positive side, glyphosate applied PRE and post‐emergence (POST) in GR crops have been an important tool in curbing the rate of selection and spread of many weed biotypes with evolved resistance to other herbicides, especially ACCase and ALS inhibitors 29–32. However, the overreliance on glyphosate to control herbicide‐resistant weeds contributed to the evolution of multiple resistance in populations (i.e.…”

Reduced sensitivity to paraquat evolves under selection with low glyphosate doses in Lolium rigidum

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