Efficacy of 2,4-D, Dicamba, Glufosinate and Glyphosate Combinations on Selected Broadleaf Weed Heights

Palmer amaranth, sicklepod and pitted morningglory are the three most common and troublesome weeds in soybean in South Carolina. They exhibit very aggressive growth capabilities and if left uncontrolled in fields will cause significant reductions in soybean yields. Dicamba and 2,4-D herbicides are currently having a resurgence in usage due to the recent commercialization of soybean trait technologies with tolerance to these herbicides. Dicamba and 2,4-D when tank mixed with glufosinate and glyphosate may offer additional weed control to resistant weeds through the process of herbicide synergism. Greenhouse experiments were conducted in 2013 at Edisto Research and Education Center near Blackville, SC to evaluate the efficacy of glyphosate, glufosinate, dicamba and 2,4-D treatments alone and in combination on Palmer amaranth, sicklepod, and pitted morningglory at selected heights. Results suggested that glufosinate alone provided the overall best control for all 3 weed species. Glyphosate alone provided the lowest control of all 3 species at all heights. Synergism or improved sicklepod control was observed when glufosinate was tank mixed with dicamba. However, as sicklepod increased in height, glufosinate + 2,4-D or dicamba combination offered the best control compared to glufosinate alone (90% versus 86% in 20 cm plants and 87% versus 85% in 30 cm plant). In the 5 cm Palmer amaranth, decreased control was observed when glyphosate or glufosinate was tank mixed with 2,4-D. These experiments showed that glufosinate alone and/or in combination with 2,4-D or dicamba was the overall best treatment on the three broadleaf weed species.