Emergence of grasses late in the season has become a problem in glyphosate-resistant (GR) soybean production in the southern US. 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 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 paraquatat 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 (EPOST) at 0.84 kg·aeha-1 followed by (fb) glyphosate late postemergence (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-meto- lachlor 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 3346, 6136, and 6916 kg·ha-1 in 2011, 2012, and 2013, respectively and
Reddy, K.N. and Norsworthy, J.K. (2010) Glyphosate-Resistant Crop Production Systems: Impact on Weed Species Shifts. In: Nandula, V.K., Ed., Glyphosate Resistance in Crops and Weeds: History, Development, and Management, John Wiley & Sons, Inc., Hoboken, 165-184. http://dx.doi.org/10.1002/9780470634394.ch9
Kurtz, M.E., Yamaji, Y. and Deloach, Y.T. (2009) KIH-485 (Pyroxasulfone): Broadleaf Signalgrass (Urochloa platyphylla) Control with Early Pre-Plant Applications in Minimum and Conventional Tillage Corn. Proceedings of Southern Weed Science Society, 62, 327.
Walsh, M.J., Fowler, T.M., Crowe, B., Ambe, T. and Powles, S.B. (2011) The Potential for Pyroxasulfone to Selectively Control Resistant and Susceptible Rigid Ryegrass (Lolium rigidum) Biotypes in Australian Grain Crop Production Systems. Weed Technology, 25, 30-37. http://dx.doi.org/10.1614/WT-D-10-00091.1
Mueller, T.C. and Steckel, L.E. (2011) Efficacy and Dissipation of Pyroxasulfone and Three Chloroacetamides in a Tennessee Field Soil. Weed Science, 59, 574-579. http://dx.doi.org/10.1614/WS-D-11-00003.1
Reddy, K.N. and Boykin, J.C. (2010) Weed Control and Yield Comparisons of Twin- and Single-Row Glyphosate-Resistant Cotton Production Systems. Weed Technology, 24, 95-101. http://dx.doi.org/10.1614/WT-D-09-00044.1