Diflufenican is a selective phenyl ether, Group 12 herbicide. There is limited information on the weed control efficacy of diflufenican and the potential improvement in weed control when co-applied with isoxaflutole. Three field studies were conducted in Ontario to evaluate isoxaflutole, diflufenican, and their combinations applied preemergence (PRE) for weed control in corn. Isoxaflutole at 52.5, 79, and 105 g ai ha⁻¹ provided effective control of velvetleaf (83-89%, 91-98%, and 92-97%), green pigweed (73-85%, 85-91%, and 94-97%), common ragweed (81-86%, 93-97%, and 95-97%), and common lambsquarters (88-89%, 96-99%, and 98-100%) evaluated at 2, 4, and 8 weeks after treatment (WAT), respectively. Diflufenican alone at 75-150 g ai ha⁻¹ provided ≤3% control of velvetleaf, ≤38% of green pigweed, ≤7% of common ragweed, and ≤20% of common lambsquarters. Isoxaflutole + diflufenican mixtures generally provided similar control to isoxaflutole applied alone. For barnyardgrass, isoxaflutole alone provided 16-75% control, while diflufenican was ineffective (<3%). The co-application of isoxaflutole + diflufenican improved control to 34-86%, with synergistic effects observed with barnyardgrass control at several rates and timings. Isoxaflutole and diflufenican, applied alone, controlled green foxtail at 15-72% and 0-12%, respectively. The co-application of isoxaflutole + diflufenican improved green foxtail control to 25-89% with synergistic responses at some rates and evaluation timings. There was minimal corn injury with the treatments evaluated. Weed interference reduced corn yield up to 69%. Weed interference with diflufenican alone resulted in corn yields of 4.57-4.75 T ha⁻¹ which were similar to the nontreated control (3.33 T ha⁻¹). Reduced weed interference with isoxaflutole alone and in mixtures with diflufenican resulted in corn yields of 8.36-10.83 T ha⁻¹ which were higher than both the nontreated control and diflufenican treatments. Overall, isoxaflutole provided consistent broadleaf weed control, while synergistic interactions with diflufenican enhanced barnyardgrass and green foxtail suppression.

Selection of effective herbicide strategies (i.e., one-pass versus two-pass and timing [preemergence versus postemergence]) is of great importance to corn growers. Field studies were conducted to evaluate overall end-of-season weed control efficacy of multiple herbicide strategies in conventional tillage corn production systems. These studies were carried out over six site-years at four locations in Wisconsin: Arlington (2018 and 2019), Brooklyn (2019), Lancaster (2019), and Janesville (2018 and 2019). Herbicide strategy treatments included one-pass preemergence, one-pass postemergence, two-pass preemergence followed by (fb) postemergence, and two-pass preemergence fb postemergence with layered residual herbicides. The weed species present at the experimental site-years included common lambsquarters, giant foxtail, giant ragweed, velvetleaf, and waterhemp. Except Arlington-2019, the herbicide strategy was not as influential for the site-years infested with common lambsquarters, giant foxtail, velvetleaf, and waterhemp species (e.g., Arlington-2018, Brooklyn-2019, Lancaster-2019), as effective overall end-of-season control (>90%) was achieved regardless of the herbicide strategy, and no significant differences were observed in the combined weed biomass across strategies. A two-pass strategy (e.g., preemergence followed by postemergence, or preemergence followed by postemergence with layered residual herbicides) was necessary for effective overall end-of-season control at the site-years infested with giant ragweed (Janesville-2018 and -2019). Weed interference reduced corn yield by 11% to 75% across site-years. Although certain weed communities can be effectively controlled by a one-pass herbicide strategy, two-pass strategies provided the greatest and most consistent overall end-of-season weed control and corn yield across all site-years, regardless of weed species composition and environmental conditions. Hence, a two-pass herbicide strategy is recommended for conventional-tillage corn production in Wisconsin to ensure effective end-of-season weed control while protecting yield potential of the crop, particularly in fields infested with moderate to high density of troublesome weeds such as giant ragweed.

Knotroot foxtail has become more prevalent and problematic in pastures and hayfields in the southeastern United States. Gaps exist in our knowledge of which herbicide practices are best for managing this species in bermudagrass forage production. This study was conducted to determine the efficacy of various ways to control knotroot foxtail in bermudagrass with herbicide applications in autumn, postemergence (POST), with and without also applying a herbicide in preemergence (PRE), in spring. The study was a randomized complete block with a factorial arrangement of treatments and included a nontreated control for both fall and spring timings. Glyphosate at two rates (0.35 or 0.7 kg ae ha−1), nicosulfuron (0.07 kg ai ha−1) + metsulfuron (0.012 kg ai ha−1), and hexazinone (1.3 kg ai ha−1) were applied alone in the fall or followed by indaziflam (0.067 kg ai ha−1) or pendimethalin (4.46 kg ai ha−1) in the spring. Three harvests were conducted throughout the growing season to evaluate weed species (knotroot foxtail, large crabgrass, and horsenettle) and bermudagrass biomass as well as overall species composition. The combination of fall and spring treatments did not affect weed species or bermudagrass biomass. Therefore, treatment main effects were analyzed by fall or spring application timing. A spring application of either pendimethalin or indaziflam increased bermudagrass biomass compared with that of the nontreated control. However, neither PRE herbicide effectively reduced knotroot foxtail biomass compared with the nontreated control, although pendimethalin did reduce season-long knotroot foxtail composition. Spring PRE herbicides are an effective tool for forage producers, but further research is needed to identify effective herbicides and additional approaches for the control of knotroot foxtail.

The methyl ester of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} applied at 0.8 to 1.4 kg ai/ha and incorporated prior to seeding winter wheat (Triticum aestivum L.) controlled downy brome (Bromus tectorum L. ♯ BROTE) better than when applied preemergence at 1.7 kg/ha in 2 of 4 yr. The emulsifiable concentrate and a granular formulation of diclofop performed similarly. Controlling downy brome improved wheat yields 3 of 4 yr. However, preplant-incorporated applications of diclofop at 1.4 kg/ha reduced wheat yield 1 of 4 yr. Greenhouse data indicated that diclofop dissipated more rapidly in moist soil than in air-dry soil.

Field studies were conducted in 2007 and 2008 at seven sites in Ohio, Indiana, and Illinois to determine the effect of PRE herbicide and POST application timing on weed control and yield of glyphosate-resistant corn. Levels of PRE herbicide included none; low—atrazine; medium—atrazine and metolachlor; and high—atrazine, mesotrione, and metolachlor. Glyphosate was applied POST when corn was 30 cm tall, or 1 or 2 wk later. Common lambsquarters, giant foxtail, and giant ragweed infested at least six of the seven sites, and other weed species occurred at two to three sites. Control of weeds at the time of POST application ranged from 48 to 91%, 58 to 99%, and 87 to 100% for the low, medium, and high levels of PRE herbicide, respectively, averaged over POST application timing. Control of giant foxtail and redroot pigweed decreased by about 20% between the second and third POST timing, averaged over PRE herbicide, but control of other weeds was similar among timings. Late-season control of common ragweed, velvetleaf, common lambsquarters, and Pennsylvania smartweed exceeded 90%, regardless of PRE herbicide or POST timing. Control of redroot pigweed, ivyleaf morningglory, and giant ragweed was as low as 74, 67, and 83%, respectively, but the high level of PRE herbicide resulted in 90 to 97% control of these weeds. An interaction between PRE herbicide and POST timing for late-season control of giant foxtail, tall waterhemp, and yellow nutsedge reflected the more effective control among POST timings from the higher levels of PRE herbicide. The overall trend in this study was for more effective weed control in PRE/POST herbicide programs with more comprehensive PRE herbicides that have substantial activity on both grass and broadleaf weeds. Highest yield occurred where the PRE treatment consisted of a two- or three-way combination of herbicides applied at 50% of the recommended rate or higher. Yield was reduced at all POST timings with atrazine alone or in the absence of PRE herbicide.

Soybean planting has occurred earlier in the Midwestern United States in recent years; however, earlier planting subjects the crop to longer durations of weed interference. This may change the optimum timing of POST glyphosate applications, or increase the need for residual herbicides applied PRE to optimize yield. A field study was conducted in 2012 and 2013 near Arlington, WI to determine the effect of planting date, residual herbicide use, and POST glyphosate timing on weed control and soybean yield. Planting dates were late April, mid-May, and early June. A PRE application of sulfentrazone plus cloransulam was applied to half the plots following each planting date. Glyphosate was applied POST to all plots at the V1, V2, V4, or R1 soybean growth stage. Planting date and glyphosate timing did not affect soybean yield in this study. However, averaged across years, planting dates, and POST glyphosate timings, yield increased from 3,280 to 3,500 kg ha−1 when a PRE herbicide with residual soil activity was used. In POST-only treatments, delaying the planting date to June decreased weed density at POST application timing from 127 to 5 plants m−2 (96%) and from 205 to 42 plants m−2 (80%) in 2012 and 2013, respectively. Where a PRE was used, total weed density at POST application timing was always less within planting date, and also declined from early to late planting date 26 to 3 plants m−2 (89%) and 23 to 6 plants m−2 (74%) in 2012 and 2013, respectively. In conclusion, both PRE herbicide use and delayed soybean planting were effective strategies to reduce the number of in-crop weeds exposed to POST glyphosate and should be considered as strategies to reduce the number of weeds exposed to POST herbicides for resistance management.

Dose–response curves for acetochlor with and without timely rotary hoeing (two passes) were derived for corn (Zea mays) fields over 2 yr. The fields were dominated by green foxtail (Setaria viridis), which constituted 73 to 86% of the weed vegetation, but also contained minor populations of common lambsquarters (Chenopodium album), Pennsylvania smartweed (Polygonum pensylvanicum), and redroot pigweed (Amaranthus retroflexus). In the absence of herbicide, rotary hoeing achieved about 50% weed control. In the absence of rotary hoeing, weed control averaged > 90% at the full label rate of acetochlor (3 kg ai/ha on clay loam soil). With two timely rotary hoeings, however, this same level of control was achieved with only 1 kg/ha acetochlor. Given the suite of weed species present in these experiments, timely rotary hoeing substituted for 67% of the label rate of acetochlor. Timeliness of rotary hoeing operations also provided consistency of results from one year to the next.

Field experiments were conducted in 2011 and 2012 in Belle Glade, FL to evaluate the response of sweet corn and weed control to pyroxasulfone on high-organic-matter soils in the Everglades Agricultural Area (EAA) of southern Florida with the use of dose-response curves. Pyroxasulfone was applied PRE at 31.25, 62.5, 125, 250, 500, and 1,000 g ai ha−1 on soil with 80% organic matter. Dose-response curves based on a three-parameter log-logistic model were used to determine pyroxasulfone rate required to provide 90% control (ED90) of spiny amaranth, common lambsquarters, and common purslane in sweet corn. The ED90 values for spiny amaranth, common lambsquarters, and common purslane control were 209, 215, and 194 g ha−1 of pyroxasulfone, respectively, at 21 d after treatment (DAT). At 42 DAT, the ED90 values for spiny amaranth, common lambsquarters, and common purslane control were 217, 271, and 234 g ha−1 of pyroxasulfone, respectively. Sweet corn yield increased with increasing rates of pyroxasulfone. An estimated 214 g ha−1 of pyroxasulfone was required to maintain sweet corn yield at 90% level of the weed-free yield. In addition, pyroxasulfone did not result in sweet corn injury. These results indicate that pyroxasulfone can provide effective weed control in sweet corn on high-organic-matter soils of the EAA.

Nitrous oxide (N2O) is a potent greenhouse gas with implicationfor climate change. Agriculture accounts for 10% of all greenhouse gasemissions in the United States, but 75% of the country's N2Oemissions. In the absence of PRE herbicides, weeds compete with soybean foravailable soil moisture and inorganic N, and may reduce N2Oemissions relative to a weed-free environment. However, after weeds arekilled with a POST herbicide, the dead weed residues may stimulate N2O emissions by increasing soil moisture and supplying carbonand nitrogen to microbial denitrifiers. Wider soybean rows often have moreweed biomass, and as a result, row width may further impact how weedsinfluence N2O emissions. To determine this relationship, fieldstudies were conducted in 2013 and 2014 in Arlington, WI. A two-by-twofactorial treatment structure of weed management (PRE + POST vs. POST-only)and row width (38 or 76 cm) was arranged in a randomized complete blockdesign with four replications. N2O fluxes were measured fromstatic gas sampling chambers at least weekly starting 2 wk after plantinguntil mid-September, and were compared for the periods before and after weedtermination using a repeated measures analysis. N2O fluxes werenot influenced by the weed by widthinteraction or width before termination, after termination,or for the full duration of the study at P ≤ 0.05. Interestingly, weobserved that POST-only treatments had lower fluxes on the sampling dayimmediately prior to POST application (P = 0.0002), but this was the onlyincidence where weed influenced N2O fluxes, andoverall, average fluxes from PRE + POST and POST-only treatments were notdifferent for any period of the study. Soybean yield was not influenced by width (P = 0.6018) or weed by width (P = 0.5825), but yield was 650 kg ha−1higher in the PRE + POST than POST-only treatments (P = 0.0007). Theseresults indicate that herbicide management strategy does not influence N2O emissions from soybean, and the use of a PRE herbicideprevents soybean yield loss.