Evaluation of 2,4-D-Choline Based Herbicide Systems in 2,4-D Tolerant Soybean (<i>Glycine max</i> L.)

Abstract

Weeds are the most limiting factor in soybean production in South Carolina. With early emergence and rapid growth, weeds effectlively compete for water, nutrients, and light resources. The recent evolution of herbicide resistant weeds has made it increasingly difficult for growers to effectively control weeds in soybean. Glyphosate and ALS-resistant Palmer amaranth biotypes have spread rapidly throughout South Carolina, especially in areas where resistance management is lacking. Soybean varieties have been recently developed with tolerance to 2,4-D. Field experiments were conducted at the Clemson University Edisto Research and Education Center located near Blackville, SC in 2012 and 2013 to evaluate selected 2,4-D choline based herbicide programs for weed management in 2,4-D tolerant soybean. Overall, all herbicide treatments were effective in controlling weeds at the POST2 timing. Palmer amaranth control was excellent; however, pitted morningglory was the most difficult. The 2,4-D plus glyphosate pre-mixture provided excellent control for all three weed species with >95% control at POST2 timing. In these treatments, the rate of 2,4-D choline plus glyphosate (1.09 kg ae ha −1 or 1.64 kg ae ha −1) did not have a significant effect on weed control (P = 0.3772). There was a decrease in pitted morningglory control 3 WAP in 2012 vs 2013 in plots treated with S-metolachlor + fomesafen because of a lack of activating soil moisture in 2012. Results from this study showed that all treatments evaluated provided good to excellent control of all 3 weed species. Based on the herbicide programs evaluated in the study, herbicide resistant weeds, such as Palmer amaranth, can be effectively controlled when treated at the correct growth stage.

Palmer Amaranth (<i>Amaranthus palmeri</i> S. Wats.) and Pitted Morningglory (<i>Ipomoea lacunosa</i> L.) Control in Dicamba Tolerant Soybean (<i>Glycine max</i> L.)

“…which was similar to what was observed by Joseph et al [20] during the same study period. Data were presented separately by year if a significant treatment by year interaction was observed.…”

“…Visual soybean injury was less than 5% for all treatments and studies (data not shown). The total rainfall received at the study sites in 2012 and 2013 was 680 mm and 647 mm, respectively [20]. Similar to studies conducted by Joseph et al [20], rainfall was also lower in June and July of 2012 compared to the same period in 2013 at the study sites.…”

Efficacy of Selected Herbicide Programs in 2,4-D Tolerant Cotton (<i>Gossypium hirsutum</i> L.)

“…a Agricultural Sciences (TRT 2 -6) that included 2,4-D choline at POST1 provided 94% to 99% control of pitted morningglory; however, in treatments without 2,4-D choline (TRT 7 -9), control declined to 85% to 89% for 2012 (Table 4). In a similar study, Merchant [21] found that the control of pitted morningglory increased when an auxinic herbicide was mixed with glufosinate rather than sprayed alone. At 2 WAP2, control of pitted morningglory was greater than 90% in 2012 with all treatments (TRT 2 -6) containing 2,4-D choline and glyphosate combinations (Table 4).…”