Field studies were conducted during the 2002 thru 2004 growing seasons at two locations in the south-central Texas cotton-production region to evaluate trifloxysulfuron and trifloxysulfuron plus prometryn in combination with either S-metolachlor or glyphosate or both for weed control and cotton response. Cotton leaf burn (13 to 19%) was noted in 2002 at one location with trifloxysulfuron plus prometryn applied late POST-directed (LPDIR). Herbicide combinations that included trifloxysulfuron controlled barnyardgrass, hemp sesbania, yellow nutsedge, Palmer amaranth, smooth pigweed, ivyleaf morningglory, pitted morningglory, and smellmelon at least 80% in most instances. Glyphosate applied early POST over-the-top (EPOTT) and mid-POST over-the-top (MPOTT) at 0.84 kg ai/ha followed by trifloxysulfuron plus prometryn at 1.1 kg ai/ha applied LPDIR controlled the above-mentioned weeds plus Texas panicum at least 94%. No other herbicide systems provided effective control (greater than 79%) of Texas panicum. Higher cotton yields in 2002 were obtained with herbicide systems that included glyphosate alone or glyphosate plus S-metolachlor applied EPOTT or LPOTT followed by trifloxysulfuron plus prometryn applied LPDIR, whereas in 2003, none of the herbicide systems increased yield over the nontreated check.

Experiments were conducted at the Lonoke Extension and Applied Research Center greenhouse at Lonoke, AR, to evaluate the effects of urea ammonium nitrate (UAN) on bispyribac and penoxsulam efficacy on barnyardgrass, hemp sesbania, and broadleaf signalgrass. Herbicide treatments included bispyribac at 17.9 or 35.8 g ai/ha or penoxsulam at 24.4 or 48.9 g ai/ha tank mixed with (1) no adjuvant, (2) a nonionic organosilicone (OSL) adjuvant at 0.125% v/v, (3) a methylated seed oil/organosilicone (MSO/OSL) adjuvant at 0.37 L/ha, (4) a proprietary blend of MSO/OSL/UAN at 2% v/v, (5) UAN at 2% v/v, (6) OSL at 0.125% plus UAN at 2% v/v, or (7) MSO/OSL at 0.37 L/ha plus UAN at 2% v/v. In addition to these adjuvants, penoxsulam was also applied with crop oil concentrate (COC) at 2.34 L/ha and with COC at 2.34 L/ha plus UAN at 2% v/v. The addition of UAN to either herbicide plus an adjuvant increased herbicide efficacy on barnyardgrass in the greenhouse, with 95 to 99% biomass reduction of three- to four-leaf barnyardgrass and 88 to 92% biomass reduction of one- to three-tiller barnyardgrass. UAN did not generally increase efficacy on hemp sesbania, as control was 90% or higher with treatments containing either herbicide and a recommended adjuvant. Adding UAN did not increase efficacy on broadleaf signalgrass. Broadleaf signalgrass control was highly variable and no treatment provided more than 65% biomass reduction.

Field experiments were conducted at Fayetteville, AR, in 1997, 1998, and 1999 to evaluate the degree of interspecific interference between drill-seeded, glyphosate-resistant soybean and hemp sesbania as influenced by soybean population, hemp sesbania density, and a single glyphosate application. Soybean was planted at 247,000, 430,000, and 618,000 seed ha−1 with early-season emergence of 217,000, 371,000, and 521,000 plants ha−1. Hemp sesbania densities were 0, 4, 10, and 16 plants m−2 in combination with 0 and 1.12 kg ai ha−1 glyphosate applied at the V4 to V6 soybean growth stage. Untreated hemp sesbania produced a maximum of 49 million seed ha−1 with 217,000 soybean ha−1, whereas seed production of glyphosate-treated hemp sesbania ranged from 2.8 to 0.6 million seed ha−1 with 217,000 and 521,000 soybean ha−1, respectively. Soybean seed yield was reduced 43% by 16 untreated hemp sesbania m−2, while glyphosate-treated hemp sesbania did not reduce seed yield. Averaged over all untreated hemp sesbania densities, soybean yield loss was reduced from 44 to 22% by increasing the soybean population from 217,000 to 521,000 plants ha−1. Because of the absence of soybean yield loss at 521,000 soybean ha−1, this density appears beneficial when using a single application of glyphosate to provide season-long weed control. However, a single glyphosate application in combination with a high soybean density did not completely prevent hemp sesbania seed production, and the seeding rate required to achieve a stand of 521,000 plants ha−1 would not be affordable; thus, alternate management methods targeting hemp sesbania must be employed to prevent an increase in the number of seed in the soil seedbank and to prevent a potential shift in the weed spectrum.