Glyphosate-resistant (GR) Palmer amaranth is a troublesome weed that can emerge throughout the soybean growing season in Nebraska and several other regions of the United States. Late-emerging Palmer amaranth plants can produce seeds, thus replenishing the soil seedbank. The objectives of this study were to evaluate single or sequential applications of labeled POST herbicides such as acifluorfen, dicamba, a fomesafen and fluthiacet-methyl premix, glyphosate, and lactofen on GR Palmer amaranth control, density, biomass, seed production, and seed viability, as well as grain yield of dicamba- and glyphosate-resistant (DGR) soybean. Field experiments were conducted in a grower’s field infested with GR Palmer amaranth near Carleton, NE, in 2018 and 2019, with no PRE herbicide applied. Acifluorfen, dicamba, a premix of fomesafen and fluthiacet-methyl, glyphosate, or lactofen were applied POST in single or sequential applications between the V4 and R6 soybean growth stages, with timings based on product labels. Dicamba applied at V4 or in sequential applications at V4 followed by R1 or R3 controlled GR Palmer amaranth 91% to 100% at soybean harvest, reduced Palmer amaranth density to as low as 2 or fewer plants m−2, reduced seed production to 557 to 2,911 seeds per female plant, and resulted in the highest soybean yield during both years of the study. Sequential applications of acifluorfen, fomesafen and fluthiacet premix, or lactofen were not as effective as dicamba for GR Palmer amaranth control; however, they reduced seed production similar to dicamba. On the basis of the results of this study, we conclude that dicamba was effective for controlling GR Palmer amaranth and reduced density, biomass, and seed production without DGR soybean injury. Herbicides evaluated in this study had no effect on Palmer amaranth seed viability.

Japanese stiltgrass is regarded as one of the most troublesome invasive species in the United States. It is commonly found invading forested areas; however, more recently it has been noted to be invading golf course roughs and out-of-play areas. The purpose of this study was to evaluate POST herbicide control of Japanese stiltgrass in golf course and highly maintained turfgrass facilities. None of the treatments provided >80% Japanese stiltgrass control 2 wk after treatment (WAT). At 4 WAT >80% Japanese stiltgrass control was observed with MSMA, MSMA + metribuzin, amicarbazone, and sethoxydim, whereas metsulfuron, pinoxaden, and imazapic provided minimum control. By 8 WAT, MSMA, MSMA + metribuzin, amicarbazone, and sethoxydim provided >98% control, whereas quinclorac, metsulfuron, pinoxaden, and imazapic provided no visible control. Thiencarbazone-methyl + foramsulfuron + halosulfuron-methyl, and sulfentrazone provided limited (≤60%) control. This study indicates that POST control of Japanese stiltgrass can be achieved with MSMA, MSMA + metribuzin, amicarbazone, and sethoxydim. Future research should include long-term control over multiple growing seasons, repeat applications of herbicides, and evaluation of herbicides in combination for increased and longer-term Japanese stiltgrass control.

The tolerance of four established seeded common bermudagrass types to PRE and POST herbicides was evaluated. Pendimethalin at 3.4 kg ai/ha, oryzalin at 3.4 kg ai/ha, and dithiopyr at 0.8 kg ai/ha suppressed the quality of bermudagrass 8 to 16% more than oxadiazon at 4.5 kg ai/ha and prodiamine at 0.8 kg ai/ha. When interactions of PRE herbicide by bermudagrass cultivars occurred, oxadiazon, prodiamine, and pendimethalin suppressed the quality of ‘common’ and ‘Sahara’ 18 to 20% more than ‘Tropica’; oryzalin suppressed the quality of common and Sahara 11 to 18% more than Tropica; and dithiopyr suppressed the quality of common and Sahara 9% more than Tropic and ‘Cheyenne.’ The quality of Cheyenne treated with either oxadiazon, prodiamine, or pendimethalin was generally intermediate to the other cultivars. When POST herbicides by bermudagrass cultivar interactions occurred, MSMA plus metribuzin applied at 2.2 + 0.1 kg ai/ha injured common and Sahara an average of 10 to 12% higher than Tropica during 1993 and 1994. Diclofop applied at 1.1 kg ai/ha and dicamba applied at 0.6 kg ae/ha injured common 9 to 12% higher than Tropica. There was no difference in injury to cultivars when treated with 2,4-D plus mecoprop plus dicamba at 1.1 + 0.6 + 0.1 kg ae/ha. In general, Tropica was affected least by PRE and POST herbicide treatments, while common and Sahara cultivars were affected the most.

2,4-DB ester had been widely used for winter annual broadleaf weed control in seedling alfalfa in the western United States, but was replaced commercially by the amine formulation in 1990. Field studies conducted in the high desert region of southern California confirmed previous reports that 2,4-DB amine is not as effective as the ester formulation. Two methods were found to improve the weed control performance of 2,4-DB amine: 1) application at earlier alfalfa growth stages and 2) the addition of adjuvant. Applications made at the three-trifoliate leaf stage of the alfalfa were more than three times as effective as applications made at the eight-trifoliate leaf stage. When adjuvants were added to the amine formulation, weed control was improved 50 to 97%.