Resistant weeds, the appropriate use of herbicides and integrated weed management strategies are highlighted topics in the new white paper, “Overlapping Residual Herbicides,” written by Purdue University Associate Professor of Weed Science Bryan Young. The white paper is now available online at www.FMCcrop.com/OverlapSystem.

“The practice of applying two effective residual herbicide sites of action in combination or the concept of using effective residual herbicides in sequential overlapping applications would both be considered a best management practice to deter the development of herbicide-resistant weeds,” writes Young.

The white paper includes research related to glyphosate-resistance in reference to the three most problematic weeds confronting famers in the major corn and soybean production areas of the United States: waterhemp, Palmer amaranth and horseweed (or marestail). These aggressive weed species can reduce soybean yields by 40 percent or more and have become problematic for growers due to prolific seed production, continuous weed emergence throughout the growing season, ease of seed dispersal and ease of overcoming or escaping herbicide-based management tactics. Soil-applied residual herbicides are the most frequently recommended because of the multiple benefits, which are further explored in the white paper.

Young concludes the white paper by summarizing that “without the use of residual herbicides for weed management, farmers are risking lost crop yield due to weed competition and continued movement towards more weed resistance to postemergence herbicides. However, only those weed management programs that carefully select the most effective soil-residual herbicides and apply them in a manner to optimize their contribution to weed management (ie overlapping residuals) will realize the greatest benefits.”

Young starts the white paper by writing, “Weed infestations in agronomic fields are dynamic and continually evolve in response to the weed management tactics that farmers implement. Prior to the adoption of glyphosate-resistant corn and soybean rotations, the most problematic weed species reported by farmers were foxtail, velvetleaf, and cocklebur (Kruger et al. 2009).”

He then mentions the problem weeds of today. “Currently, the most problematic weed species confronting farmers in the major corn and soybean production regions of the U.S. are waterhemp, Palmer amaranth, and horseweed (aka marestail), which is a direct result of the evolution and subsequent wide-scale spread of resistance to glyphosate in these weed species (Heap 2014; Prince et al. 2012).”

The white paper is available online at www.FMCcrop.com/OverlapSystem.