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ARS Home » Southeast Area » Stoneville, Mississippi » Crop Production Systems Research » Research » Publications at this Location » Publication #312942
Title: Late-season grass weed management with in-crop and post-harvest herbicides in twin-row glyphosate-resistant soybean

Author
item Reddy, Krishna
item Bryson, Charles
item Nandula, Vijay

Submitted to: American Journal of Plant Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2015
Publication Date: 1/22/2015
Citation: Reddy, K.N., Bryson, C.T., Nandula, V.K. 2015. Late-season grass weed management with in-crop and post-harvest herbicides in twin-row glyphosate-resistant soybean. American Journal of Plant Sciences. 6:213-218.

Interpretive Summary: Emergence of grasses late in the season has become a problem in glyphosate-resistant (GR) soybean production in the southern US. To reduce the risk of late-season weeds and to sustain crop yields, it is imperative to develop strategies to manage these weeds. Scientists at the USDA-ARS, Crop Production Systems Research Unit in Stoneville, MS conducted a 3-yr field study to determine the efficacy of pyroxasulfone applied as preemergence coupled with post-harvest herbicides on late-season grass weeds and yield in twin-row GR soybean. Pendimethalin and paraquat were applied after soybean harvest (post-harvest) and five pyroxasulfone-based herbicides were applied in-crop in twin-row soybean. Browntop millet, Digitaria spp., and junglerice densities at 2 weeks after late postemergence, grass weed dry biomass at harvest, and soybean yield were similar regardless of post-harvest herbicides in all three years. At 2 weeks after late postemergence, browntop millet, Digitaria spp. and junglerice densities were reduced in all five in-crop herbicide treatments compared with no herbicide plot in all three years. The five herbicide treatments reduced grass weed dry biomass by at least 87, 84, and 99% in 2011, 2012, and 2013, respectively. Soybean yield was higher with all five in-crop herbicide treatments compared to no herbicide control in all three years. This study demonstrated that these grass weeds can be reduced with pyroxasulfone-based in-crop herbicide programs in twin-row GR soybean.

Technical Abstract: A 3-yr field study was conducted from 2011 to 2013 at Stoneville, MS to determine efficacy of post-harvest and pyroxasulfone-based in-crop herbicides on late-season grasses and yield in twin-row glyphosate-resistant (GR) soybean. Experiments were conducted in a split-plot arrangement of treatments in a randomized complete block design with fall herbicides (with and without pendimethalin at 1.12 kg ai ha-1 and paraquat at 0.84 kg ai ha-1) as main plots and in-crop herbicides as subplots with four replications. The six in-crop herbicide programs were: glyphosate applied early postemergence (POST) (EPOST) at 0.84 kg ae ha-1 followed by (fb) glyphosate late POST (LPOST) at 0.84 kg ha-1 with and without pyroxasulfone preemergence (PRE) applied at 0.18 kg ai ha-1, pyroxasulfone PRE fb glyphosate at 0.84 kg ha-1 LPOST or glyphosate at 0.84 kg ha-1 + S-metolachlor at 1.68 kg ai ha-1 EPOST, pyroxasulfone PRE fb S-metolachlor at 1.12 kg ha-1 + fomesafen at 0.27 kg ai ha-1 EPOST fb clethodim at 0.14 kg ai ha-1, and a no-herbicide control. Browntop millet, Digitaria spp., and junglerice densities at 2 weeks after LPOST, grass weed dry biomass at harvest, and soybean yield were similar regardless of post-harvest herbicides in all three years. At 2 weeks after LPOST, browntop millet, Digitaria spp. and junglerice densities were greatly reduced in all five in-crop herbicide treatments compared with no herbicide plot in all three years. Grass weed dry biomass in no-herbicide plots was 3,346, 6,136, and 6,916 kg ha-1 in 2011, 2012, and 2013, respectively and the five herbicide treatments reduced grass weed dry biomass by at least 87, 84, and 99% in 2011, 2012, and 2013, respectively. Soybean yield was higher with all five in-crop herbicide treatments compared to no herbicide control in all three years. These results indicate that browntop millet, Digitaria spp., and junglerice infestations can be reduced with pyroxasulfone-based in-crop herbicide programs in twin-row GR soybean.