Biotypes of Palmer amaranth that are resistant to acetolactate synthase (ALS) inhibitor are becoming widespread in western Nebraska. There are limited effective postemergence (POST) herbicides labeled for ALS-inhibitor-resistant Palmer amaranth control in dry edible bean. The objective of this study was to evaluate the efficacy of dimethenamid-P in a sequential preemergence (PRE) fb followed by (fb) POST program at two POST application timings, the first and third trifoliate stages (V1 and V3, respectively), for controlling ALS-inhibitor-resistant Palmer amaranth in dry edible bean. A field study was conducted in 2019, 2020, and 2021 in Scottsbluff, NE. PRE-alone applications of pendimethalin + dimethenamid-P provided inconsistent Palmer amaranth control. Dimethenamid-P applied POST following a PRE application of pendimethalin + dimethenamid-P provided effective (>90%) Palmer amaranth control at 4 wk after V3 only at the V1 application timing in 2019. In 2020 and 2021 dimethenamid-P applied POST at V1 and V3 following a PRE application of pendimethalin + dimethenamid-P provided 99% and 98% Palmer amaranth control at 4 wk after V3, and 98% and 94% Palmer amaranth control at harvest, respectively. Palmer amaranth biomass was reduced by 95% to 99% and by 96% to 98% compared with the -nontreated control when dimethenamid-P was applied POST at V1 and V3, respectively, following a PRE application of pendimethalin + dimethenamid-P in 2020 and 2021. Application of a mixture of dimethenamid-P with imazamox + bentazon POST provided similar results to those of the fomesafen-containing treatments and dimethenamid-P alone POST. Dimethenamid-P applied POST following a PRE application of pendimethalin + dimethenamid-P resulted in similar yield as the fomesafen-containing treatments. If fomesafen is not an option due to the crop rotation interval restriction, using dimethenamid-P in a sequential PRE fb POST program is the only effective alternative to control ALS-inhibitor–resistant Palmer amaranth in Nebraska. The use of dimethenamid-P in a sequential PRE fb POST program, alone or mixed with foliar-active herbicides should be considered by dry edible bean growers who are dealing with ALS-inhibitor-resistant Palmer amaranth.

Although Palmer amaranth is currently not widespread in most dry edible bean−producing states in the United States, it is widespread in western Nebraska, a major dry edible bean−producing region. There is currently a lack of research on management and biology of Palmer amaranth within dry edible bean production. The objective of this study was to quantify the impact of season-long Palmer amaranth interference on yield of dry edible bean and seed production of Palmer amaranth. A field study was conducted in Scottsbluff, NE, in 2020 and 2021. Palmer amaranth interference at densities of 0, 0.2, 0.3, 0.5, 1, and 2 plants m−1 row of dry edible bean was evaluated. Palmer amaranth interference reduced dry edible bean yield by 77% at a weed density of 2 plants m−1 row compared to the weed-free control, and a 5% yield reduction threshold was estimated to occur at a Palmer amaranth density of 0.02 plants m−1 row. Yield reduction occurred primarily through a reduction in the number of pods per plant as Palmer amaranth density increased. Palmer amaranth plants produced 91,000 to 376,000 seeds per plant depending on densities, and as many as 140,000 seeds m−2. Study results will help farmers and other stakeholders estimate Palmer amaranth interference within their fields, and may help justify the economic cost of incorporating additional Palmer amaranth management practices.

Metobromuron is a major preemergence herbicide controlling mainly broadleaf weeds in common bean production in Ontario. Rainstorms at the seedling stage may splash metobromuron on the plants which results in serious injury, reduced plant stand, and low seed yield. This study determined the appropriate rates of metobromuron for identification of germplasm tolerant to the herbicide. Metobromuron of 0, 0.28, and 0.56 kg ai ha−1 in the glasshouse and 0, 0.28, 0.42, and 0.56 kg ha−1 in the field were applied POST at the unifoliolate stage of 30 bean cultivars. A significant linear effect of herbicide rate on plant injury and recovery was detected. Plant growth was reduced significantly on sensitive cultivars. Two cultivars, Taylor Hort’ and ‘UI 51’, and several plant introductions were tolerant to metobromuron. A rate range of 0.42 to 0.56 kg ha−1 of metobromuron would be appropriate to separate tolerant from sensitive bean lines.

Imazethapyr, alone and in combination with other herbicides, was applied PPI, PRE, and POST to pinto beans to determine weed control and selectivity to the crop. All of the herbicides improved pinto bean yield as compared with the unweeded control. Imazethapyr applied PPI and POST provided excellent control of black nightshade, kochia, Russian thistle, prostrate pigweed, and redroot pigweed. Barnyardgrass control with imazethapyr ranged from 58 to 96% and increased to 98% or greater when imazethapyr was combined with metolachlor, pendimethalin, trifluralin, or EPTC. Pinto bean yield was not reduced from any herbicide treatment compared to the handweeded control.

Common ragweed is a major problem in white bean production systems in Ontario. The influence of time of emergence and density of common ragweed on white bean growth and seed yield was examined in Ontario at Elora in 1990, and at Woodstock and Staffa in 1991 and 1992. Ragweed emerged with white bean seedlings (VE) and at the second trifoliate stage of white bean (V3). Time of ragweed emergence and weed density affected white bean yield at all locations. When 1.5 ragweed seedlings m−1 of row emerged at the VE stage of crop growth 10 to 22% seed yield loss occurred. Yield losses of 4 to 9% occurred when 1.5 ragweed seedlings m−1 of row emerged at the V3 crop stage. Yield loss parameter estimates, i.e., the predicted weed-free crop yield (YWF) and the maximum yield loss (A), varied among locations and with time of ragweed emergence, whereas the parameter for yield loss at low weed density (I) was more consistent across all locations and times of weed emergence. Although I values were relatively consistent across locations and times of ragweed emergence, the standard errors associated with each estimate were large. White bean leaf area index, above-ground biomass and pod number m−2 were affected most by ragweed interference. White bean density, number of seeds per pod, and seed weight per plant were not affected by ragweed interference. Ragweed emerging at VE and V3 produced a maximum of 6000 and 1000 seeds m−2, respectively. Time of ragweed emergence may be more important than weed density when evaluating weed control options.

Field trials were conducted from 2010 through 2012 to evaluate the integration of three factors: overhead irrigation after planting great northern dry bean; three methods of seedbed preparation: no-tillage, one or two diskings; and eight weed control treatments on dry bean development and weed control. The previous crop each year was corn. Overhead irrigation with 13 mm of water immediately after herbicide application and planting in early June did not improve or reduce herbicide efficacy but where herbicides were not utilized, irrigation increased weed emergence. Soil crusting increased in 2 of 3 yr when soil was disked at a 20-cm depth before planting. Crop injury from herbicides applied PRE increased when soil crusting occurred. No tillage before planting reduced crop injury from herbicides in 2010 and 2011 and weed density in 2012. Dry bean injury was minimal from herbicides applied PRE except for flumioxazin, which reduced crop density in 2011 and 2012. Imazamox plus bentazon applied POST caused early-season dry bean injury in 2 of 3 yr and resulted in a reduction in crop seed yield compared to dimethenamid-P or halosulfuron applied PRE. As producers move away from intensive tillage before planting to reduced tillage or no-tillage production systems, the results of this experiment show that dimethenamid-P, halosulfuron, pendimethalin, and S-metolachlor can be utilized PRE to provide acceptable weed control and crop selectivity. Although flumioxazin applied PRE reduced plant density, Great Northern dry bean yields were not affected by the loss of plant stand.