Influence of Soybean (Glycine max) Population and Herbicide Program on Palmer Amaranth (Amaranthus palmeri) Control, Soybean Yield, and Economic Return

Abstract

Palmer amaranth (Amaranthus palmeri S. Wats) has become one of the most prominent and difficult weeds to control in soybean (Glycine max (L.) Merr.) in North Carolina. A survey was conducted in North Carolina during fall 2010 to estimate the magnitude of this problem. Palmer amaranth was present in 39% of 2,512 fields representing 0.24% of soybean ha in North Carolina. In recent years, growers have reduced soybean seeding rates in an effort to decrease production costs associated with technology fees. However, given the increase in prevalence of Palmer amaranth and the difficultly in controlling this weed due to herbicide resistance, growers may need to reconsider reductions in seeding rates. Therefore, research was conducted during 2010 and 2011 to determine if Palmer amaranth control, soybean yield, and economic return were affected by soybean plant population, preemergence (PRE) and postemergence (POST) herbicides, and herbicide resistant traits (glufosinate-resistant and glyphosateresistant cultivars). Applying PRE or POST herbicides and increasing soybean population increased Palmer amaranth control, soybean yield, and economic return when compared with POST herbicides only or when lower soybean populations were present. Efficacy of glufosinate and glyphosate did not vary in most instances, most likely because these herbicides were applied timely, and the frequency of glyphosate resistance did not exceed 10% in these fields.

Long‐term Management of Palmer Amaranth with Herbicides and Cultural Practices in Cotton

“…A uniform mixture of natural infestations of GS and GR Palmer amaranth were present at both locations. Frequency of GR Palmer amaranth was less than 10% at the start of the experiment, confirmed through previous work (Hoffner et al, 2012; Inman et al, 2016). Soil was a Goldsboro fine sandy loam (fine‐loamy, silicious, subactive, thermic Aquic Paleudults) with humic matter content of 0.5% at Kingsboro and a Roanoke loam (fine, mixed, semi‐active, thermic Typic Endoaquults) with humic matter content of 2.8% at the Fountain Farm.…”

“…These data show the long‐term value of preventing weed seed production (Norsworthy et al, 2014). Initial soil core data were not collected; however, through previous work and anecdotal evidence we can confirm this study was initiated in fields with uniform populations of Palmer amaranth with a relatively low frequency of glyphosate resistance (Hoffner et al, 2012; Inman et al, 2016).…”