A large-plot field experiment was conducted at Keiser, AR, from fall of 2010through fall of 2013 to understand to what extent soybean in-crop herbicideprograms and postharvest fall management practices impact Palmer amaranthpopulation density and seed production over three growing seasons. Theeffect of POST-only (glyphosate-only) or PRE followed by (fb) POST(glyphosate or glufosinate) + residual herbicide treatments were evaluatedalone and in combination with postharvest management options of soybeanresidue spreading or soil incorporation, use of cover crops, windrowingwith/without burning, and residue removal. Significant differences wereobserved between fall management practices on Palmer amaranth populationdensity each fall. The use of cover crops and residue collection and removalfb the incorporation of crop residues into soil during the formation of bedswere the most effective practices in reducing Palmer amaranth population. Incontrast, the effects of fall management practices on Palmer amaranth seedproduction were inconsistent among years. The inclusion of a PRE herbicideapplication into the herbicide program significantly reduced Palmer amaranthpopulation density and subsequent seed production each year when compared tothe glyphosate-only program. Additionally, the glufosinate-containingresidual program was superior to the glyphosate-containing residual programin reducing Palmer amaranth seed production. PRE fb POST herbicides resultedin significant decreases in the Palmer amaranth population density and seedproduction compared to POST application of glyphosate alone for all fallmanagement practices, including the no-till practice. This studydemonstrated that crop residue management such as chaff removal from thefield, the use of cover crops, or seed incorporation during bed formation incombination with an effective PRE plus POST residual herbicide program isimportant for optimizing in-season management of Palmer amaranth andsubsequently reducing the population density, which has a profound impact onlessening the risk for herbicide resistance and the consistency andeffectiveness of future weed management efforts.
