%0 Journal Article
%T Influence of Soybean (Glycine max) Population and Herbicide Program on Palmer Amaranth (Amaranthus palmeri) Control, Soybean Yield, and Economic Return
%A Amy E. Hoffner
%A David L. Jordan
%A Alan C. York
%A E. James Dunphy
%A Wesley J. Everman
%J ISRN Agronomy
%D 2012
%R 10.5402/2012/947395
%X 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 glyphosate-resistant 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. 1. Introduction Effective weed management continues to be an important component of profitable soybean production in North Carolina. In recent years, herbicide-resistant weed populations have developed and have limited the effectiveness of herbicide options for growers. Populations of Palmer amaranth and horseweed (Conyza canadensis L.) in the coastal plain of North Carolina resistant to glyphosate have been confirmed [1, 2]. Resistance of Palmer amaranth to acetolactate synthase (ALS)-inhibiting herbicides also has been confirmed in North Carolina [1, 2]. Managing herbicide-resistant weed populations continues to be a challenge, especially Palmer amaranth, where alternatives to glyphosate and ALS-inhibiting herbicides require timely application [3, 4]. During fall 2010, 242 specific sites were sampled in North Carolina to determine the geographical range of Palmer amaranth and to determine if these populations were resistant to glyphosate. Of these specific sites, 52% had Palmer amaranth present with 98% of these populations expressing resistance to glyphosate and 85% expressing resistance to thifensulfuron-methyl [5].
%U http://www.hindawi.com/journals/isrn.agronomy/2012/947395/