Corn that is resistant to aryloxyphenoxypropionate, known commercially as Enlist™ corn, enables the use of quizalofop-p-ethyl (QPE) as a selective postemergence (POST) herbicide for control of glufosinate/glyphosate-resistant corn volunteers. Growers usually mix QPE with 2,4-D choline or glufosinate or both to achieve broad-spectrum weed control in Enlist corn. The objectives of this study were 1) to evaluate the efficacy of QPE applied alone or mixed with 2,4-D choline and/or glufosinate to control glufosinate/glyphosate-resistant corn volunteers in Enlist corn and 2) to determine the effect of application time (V3 or V6 growth stage of volunteer corn) of QPE-based treatments on volunteer corn control and Enlist corn injury and yield. Field experiments were conducted in Clay Center, NE, in 2021 and 2022. Quizalofop-p-ethyl (46 or 93 g ai ha−1) applied at the V3 or V6 growth stage controlled volunteer corn by ≥88% and ≥95% at 14 and 28 d after treatment (DAT), respectively. QPE (46 g ai ha−1) mixed with 2,4-D choline (800 g ae ha−1) produced 33% less than expected control of V3 volunteer corn in 2021, and 8% less than expected control of V6 volunteer corn in 2022 at 14 DAT. Volunteer corn control was improved by 7% to 9% using the higher rate of QPE (93 g ai ha−1) in a mixture with 2,4-D choline (1,060 g ae ha−1). QPE mixed with glufosinate had an additive effect and interactions in any combinations were additive beyond 28 DAT. Mixing 2,4-D choline can reduce QPE efficacy on glufosinate/glyphosate-resistant corn volunteers up to 14 DAT when applied at the V3 or V6 growth stage; however, the antagonistic interaction did not translate into corn yield loss. Increasing the rate of QPE (93 g ai ha−1) while mixing with 2,4-D choline can reduce antagonism.

Six field experiments were established in southwestern Ontario in 2021 and 2022 to evaluate whether the addition of a grass herbicide (acetochlor, dimethenamid-p, flufenacet, pendimethalin, pyroxasulfone, or S-metolachlor) to tolpyralate + atrazine improves late-season weed control in corn. Tolpyralate + atrazine caused 12% and 5% corn injury at 1 and 4 wk after herbicide application (WAA); corn injury was not increased with the addition of a grass herbicide. Weed interference reduced corn yield 60%. The addition of a grass herbicide to tolpyralate + atrazine did not enhance velvetleaf control. The addition of acetochlor or dimethenamid-p to tolpyralate + atrazine enhanced pigweed species control 4% 4 WAA; the addition of other grass herbicides tested did not increase pigweed species control. The addition of acetochlor enhanced common ragweed control 5% at 4 WAA, and the addition of acetochlor or dimethenamid-p enhanced common ragweed control 8% at 8 WAA; the addition of other grass herbicides did not improve common ragweed control. The addition of acetochlor to tolpyralate + atrazine enhanced common lambsquarters control up to 4%; there was no enhancement in common lambsquarters control with the addition of the other grass herbicides. Tolpyralate + atrazine controlled barnyardgrass 90% and 78% at 4 and 8 WAA, respectively; the addition of a grass herbicide enhanced barnyardgrass control 9% to 10% and 21% at 4 and 8 WAA, respectively. Tolpyralate + atrazine controlled green or giant foxtail 80% and 69% at 4 and 8 WAA, respectively; the addition of a grass herbicide enhanced foxtail species control 15% to 19% and 24% to 29% at 4 and 8 WAA, respectively. This research shows that adding a grass herbicide to tolpyralate + atrazine mixture can improve weed control efficacy, especially increased annual grass control in corn production.

Herbicides are often used to terminate cover crops. Producers would like to use herbicides that work quickly, are effective, and do not increase the risk of selecting herbicide-resistant weeds. Eight experiments were conducted to determine whether mixing glyphosate (900 g a.e. ha−1) with rimsulfuron (15 g a.i. ha−1), mesotrione (100 g a.i. ha−1), or rimsulfuron + mesotrione enhances winter rye control and to ascertain whether using urea ammonium nitrate (UAN) as the herbicide carrier improves and accelerates herbicide efficacy. Winter rye control was assessed 1, 2, 3, and 4 wk after application (WAA) and biomass was measured 4 WAA. The addition of rimsulfuron, mesotrione, or rimsulfuron + mesotrione to glyphosate did not enhance winter rye control. Similarly, using UAN as the herbicide carrier did not improve or accelerate herbicide efficacy. Glyphosate alone provided the greatest level of winter rye control. The addition of rimsulfuron, mesotrione, or rimsulfuron + mesotrione to glyphosate did not increase the level or speed of control. However, mixing glyphosate with rimsulfuron, mesotrione, or rimsulfuron + mesotrione adds other modes of action without compromising winter rye control.

Successful cover crop (CC) establishment in the fall is important to maximize CC production, which is critical for achieving many objectives of CCs. Competition from winter weeds may reduce CC establishment and biomass production. A preplant herbicide, such as paraquat, at the time of CC planting in the fall will reduce winter weed pressure resulting in better establishment and growth. An experiment was conducted between 2019 and 2021 to test this hypothesis by evaluating a no-CC check, cereal rye, hairy vetch, crimson clover, and cereal rye + hairy vetch drilled with and without paraquat applied at planting (mid-October to mid-November) following either a corn or soybean crop. Visible weed suppression ratings were collected in mid-April, and total CC and weed biomass was collected in late April. More CC biomass was accumulated following corn than soybean, regardless of preplant herbicide application, because corn is typically harvested before soybeans. Therefore, CCs should be planted early to accumulate more biomass. Weed suppression varied by weed species from all factors, but in general weed suppression was best from a CC mixture containing cereal rye and paraquat applied at planting. If weed suppression is the main goal of the CC, then a preplant herbicide at CC planting is recommended. However, if CC weed suppression goals can be achieved through biomass accumulation, no preplant herbicide is needed. This information is useful for producers to achieve various CC objectives while managing costs.

More growers across the U.S. Midwest are considering interseeding or overseeding cover crops into corn for soil health purposes. One challenge of this practice is the potential injury from soil residual herbicides applied preemergence (PRE) for weed control in corn to the interseeded and overseeded cover crop species. Field-treated soil was collected in 2021 and 2022 at Janesville, WI, and Lancaster, WI, to investigate the impact of PRE residual herbicides on establishment of interseeded and overseeded cover crops via greenhouse bioassay. Soil samples (0 to 5 cm depth) were collected from field experiments at 0, 10, 20, 30, 40, 50, 60, and 70 days after treatment (DAT). Treatments consisted of 14 single and multiple sites of action (SOAs) PRE herbicides plus a nontreated check (NTC). Four bioindicator cover crop species were used in the greenhouse bioassay: annual ryegrass, cereal rye, radish, and red clover. Cover crop biomass was collected 28 d after bioassay seeding. Cover crop species responded differently across herbicide treatments. Annual ryegrass and cereal rye were sensitive to treatments containing herbicide Group 15, whereas Groups 2, 4, 5, 14, and 27 had minimal impact on their establishment when field soil was collected at 30 DAT (interseeding scenario) and 70 DAT (overseeding scenario) compared to the NTC. Radish and red clover were sensitive to herbicide Groups 2, 4, and 27, whereas Groups 5, 14, and 15 had minimal impact on their establishment. Annual ryegrass, radish, and red clover were more sensitive to PRE herbicides containing two and three SOAs than to herbicides with a single SOA. On the basis of these greenhouse bioassay results, cover crop species should be carefully selected depending on the soil residual herbicide when interseeded and overseeded into corn. Field studies will be conducted to validate these results and support recommendations to growers interested in this system.

Limited research has been directed at evaluating the ability of single cover crop plantings to suppress weeds in crops beyond the initial field season. Thus, this experiment was conducted to investigate the ability of a second-year self-regenerated annual and second-year perennial cover crop planting to suppress weeds during the critical period for weed control (CPWC) in soybean crops. Whole-plot treatments included 1) conventional till, 2) no-till with cover crop residue, 3) living mulch + cover crop residue, and 4) living mulch + winter-killed residue. Subplot treatments involved weed management intensity: a) no weed management (weedy), b) weeds manually removed through the CPWC (third node soybean stage; V3), and c) weeds manually removed until soybean canopy closure (weed-free). Overall, total annual cover crop biomass during the second field season was comparable to biomass obtained from direct seeded stands during the initial field season. All cover crop treatments reduced total weed biomass through the CPWC compared to conventional till. Soybean yield was low across all treatments in this experiment. Still, yield was similar between cover crop and conventional till treatments at one site-year, however, yields were lower in all cover crop treatments at the other site-year.

Herbicide resistance coupled with a dearth of selective herbicide options has increased the complexity of annual bluegrass control in hybrid bermudagrass putting greens. Cumyluron, endothall, and methiozolin are herbicides that control annual bluegrass by inhibiting novel sites of action compared with the herbicides currently used for turfgrass management in the United States. However, peer-reviewed literature contains no information on hybrid bermudagrass putting green tolerance to these herbicides. Sixteen field studies were established on eight golf greens in Midlothian, VA, in 2021 and 2022 to evaluate effects of cumyluron, endothall, methiozolin, pronamide, and trifloxysulfuron on bermudagrass spring transition. The 16 studies were split equally between initiation during full dormancy versus mid-spring transition. Methiozolin applied at 500 and 1,000 g ai ha−1 typically increased the heat units (growing degree days with a base temperature of 15 C) required for hybrid bermudagrass to visibly achieve 90% green coverage (T90) when applied to fully dormant hybrid bermudagrass. This delay in green coverage was more pronounced at sites where hybrid bermudagrass vigor was seemingly reduced via abiotic stressors. Endothall was generally more injurious than all other treatments when applied to hybrid bermudagrass during mid-transition. Endothall applied at 840 g ai ha−1 injured hybrid bermudagrass for 0 to 9 d over a threshold of 30% (DOT30), depending on location. In two site-years characterized by increased abiotic stress, methiozolin applied at 1,000 g ai ha−1 caused 44 DOT30. Cumyluron never injured hybrid bermudagrass by more than 30% or delayed T90 regardless of application timing. These results indicate that methiozolin should be applied only within labeled rates to actively growing hybrid bermudagrass putting greens, cumyluron can be safely applied at 6,450 g ai ha−1 to dormant or actively growing bermudagrass greens, and endothall applications should be limited to dormant bermudagrass greens unless transient phytotoxicity is acceptable.

Smutgrass is a non-native perennial weed that is problematic because of its poor palatability to cattle and its difficulty to control once established. Limited literature exists to explain the effectiveness of herbicides other than hexazinone for smutgrass control and forage injury. This study aimed to evaluate seasonal applications of labeled herbicides used on forage for maximum smutgrass control. The second objective was to evaluate preemergent herbicides and hexazinone for their ability to control smutgrass germinating from seed. Hexazinone, nicosulfuron + metsulfuron-methyl, and glyphosate + imazapic were the most effective postemergence treatments, while quinclorac exhibited little activity on smutgrass. Common bermudagrass forage fully recovered from all treatments by 3 mo after treatment. Hexazinone, nicosulfuron + metsulfuron methyl, glyphosate, and imazapic were applied postemergence to smutgrass in spring, summer, and fall. Summer applications of hexazinone resulted in the greatest level of control, while spring treatments provided the least control. Applications of hexazinone or glyphosate resulted in the most effective smutgrass control. However, fall applications resulted in the least forage injury. Results of the study of preemergence herbicides indicate that treatments with indaziflam and hexazinone provide adequate control of germinating smutgrass seedlings in the greenhouse at 0.25×, 0.5×, and 0.75× of the lowest recommended labeled rate for seedling grass control. Indaziflam treatments prevented the emergence of any visible smutgrass seedling tissue, compared to hexazinone, which fully controlled the germinating seedlings by 21 d after treatment, whereas pendimethalin significantly reduced seedling numbers at the 0.5× and 0.75× rates.

The increasing development of herbicide resistance in weeds found in rice cropping systems has encouraged researchers to evaluate alternate herbicides to prevent and manage herbicide-resistant weed biotypes. Metribuzin is a photosynthetic-inhibiting herbicide that controls various important grass and broadleaf weeds. Several crops, including soybean, wheat, peas, and potato, have shown differential varietal responses to metribuzin. To determine whether rice has differential varietal responses to metribuzin for potential utilization in a rice breeding program, greenhouse experiments were conducted to evaluate the responses of 142 long-, medium-, and short-grain rice genotypes to the herbicide. Metribuzin was applied at 0, 22, 44, 88, 176, and 352 g ai ha−1 when rice plants were in the 3- to 4-leaf stage. Crop response regarding phytotoxicity, height reduction, and biomass reduction was evaluated. Metribuzin caused significant injury to all rice genotypes tested, but short-grain rice genotypes were, on average, more susceptible than medium- and long-grain rice genotypes. Short-grain rice genotypes generally had greater height reduction and produced less biomass than long-grain or medium-grain rice genotypes. Crop visual injury ratings were correlated with plant height reductions and biomass reductions. The results indicate that the level of metribuzin tolerance in rice is inadequate for commercial use; however, further research is needed to develop higher levels of herbicide resistance by mutagenized rice cultivars.

Russian thistle is one of the most important broadleaf weeds in the semiarid U.S. Pacific Northwest. It consumes soil water after wheat harvest, compromising the yield of the following crop. The objectives of this work were to determine the impact of post–wheat harvest herbicide application timing on Russian thistle control and of stubble height on Russian thistle postharvest control and plant dispersal. For the first objective, experiments were conducted at the Columbia Basin Agricultural Research Center, Adams, OR (CBARC), and the Lind Dryland Research Station, Lind, WA (LDRS), in 2020 and 2021. Herbicides evaluated included paraquat, glyphosate, and either bromoxynil + pyrasulfotole (CBARC) or bromoxynil + metribuzin (LDRS). The different post–wheat harvest application timings were 24 h and 1, 2, and 3 wk after harvest. For the second objective, two stubble heights (short and tall) were compared for their impact on control at CBARC and in a production field near Ione, OR. Paraquat provided the greatest control in all scenarios, with no differences in application timings or stubble height. Impacts of application timings were not clear for glyphosate or bromoxynil mixtures. For glyphosate treatments, control in short stubble was 11% greater than in tall stubble in both years. Control was also greater in short stubble for the bromoxynil + pyrasulfotole application in 2020. However, Russian thistle plant dispersal was greater in short stubble at both locations. At CBARC, plant dispersal in short stubble was 58%, compared to 18% in tall stubble. Near Ione, plant dispersal in flattened stubble was 88%, compared to 43% in nonflattened short stubble. Leaving tall stubble at harvest should be considered to reduce Russian thistle plant dispersal if the infestation is going to be left untreated after harvest; otherwise, short stubble might result in better Russian thistle control when using systemic herbicides, such as glyphosate.

Few herbicides are registered for goosegrass control in creeping bentgrass turfgrass. Topramezone controls goosegrass and is labeled for use on creeping bentgrass, but potential injury risks lead many turf managers to frequently apply it at a low-dose. This application practice increases the likelihood that topramezone treatments will be mixed with fungicide treatments. Previous research found that fungicides can reduce the activity of some herbicides, but their effects on topramezone efficacy are unknown. Four studies were established between Blacksburg, VA, and North Brunswick, NJ, in 2021 to determine whether chlorothalonil reduces goosegrass control from topramezone. In controlled environment dose-response studies the amount of topramezone needed to reduce goosegrass biomass by 50% increased from 3.04 g ha−1 to 5.27 g ha−1 when chlorothalonil (7,400 g ha−1) was added to the mixture. In field experiments, topramezone at 3.7 and 6.1 g ha−1 controlled goosegrass by 50% and 63%, respectively, at 42 d after treatment when averaged across herbicide admixtures. The addition of chlorothalonil alone and chlorothalonil plus acibenzolar-S-methyl to topramezone reduced goosegrass control from 73% to 52% and 45%, respectively, when averaged across topramezone rate. From these studies we can conclude that chlorothalonil has the potential to reduce goosegrass control when topramezone is applied at the maximum allowable rate (6 g ae ha−1) or less. This is the first report of fungicides acting to reduce herbicidal weed control efficacy in turfgrass systems.

Intermediate wheatgrass (IWG) is a cool-season perennial grass developed as a dual-purpose grain and forage crop. One barrier to adopting this crop is a lack of information on the effects of herbicides on IWG for grain production. An experiment was conducted to evaluate herbicide effects on IWG grain yield, crop injury, and weed control over 2 yr (2019 to 2021) at sites in Wisconsin, Minnesota, New York, and North Dakota. This evaluation included broadleaf herbicides registered for use on wheat: 2,4-D amine, clopyralid, MCPA, and a mixture of clopyralid + MCPA (all are categorized as Group 4 herbicides by the Weed Science Society of America). Each herbicide or mixture was applied at 1× and 2× the labeled wheat application rate to newly planted and established (1- to 5-yr-old) IWG stands in the fall or spring. Herbicides were applied during IWG tillering or jointing stages in the fall or during the jointing stage in the spring. Across site years, application timing, herbicide, and application rate showed no effect on IWG grain yield or plant injury. Broadleaf weed control ranged from 71% to 92% across herbicide treatments relative to the nontreated check at the Wisconsin site, whereas weed control at the Minnesota site was variable among treatments. At the New York site, herbicides were equally effective for broadleaf weed suppression, whereas weed pressure was very low at the North Dakota site and treatments did not affect weed cover. The results show that newly planted and established stands of IWG are tolerant to the synthetic auxin herbicides 2,4-D amine, clopyralid, and MCPA when applied during tillering or jointing in the fall or during jointing in the spring. Synthetic auxins represent a potentially useful tool for weed control in IWG cropping systems, especially for problematic broadleaf weed species.

In 2021 and 2022, research was initiated at two locations to evaluate the efficacy and safety of sulfentrazone in transplanted cabbage and broccoli. Treatments included oxyfluorfen at 560 g ha−1 applied pretransplant (PRE-T), sulfentrazone applied at 116 or 233 g ha−1 PRE-T, and S-metolachlor applied at 715 g ha−1 immediately after transplanting (POST-T) followed by (fb) oxyfluorfen applied at 210 g ha−1 postemergence (POST) 14 d after planting (DAP). The weedy cover of nontreated plots averaged between 6% (14 DAP) and 72% (42 DAP); all herbicide-treated plots averaged less than 30% cover at 42 DAP. At 14 and 28 DAP, oxyfluorfen, S–metolachlor fb oxyfluorfen, and the high rate of sulfentrazone reduced total monocotyledonous and dicotyledonous weed densities by 62% and 100%, respectively, relative to the nontreated control. The density of hairy galinsoga (in New Jersey) and combined ladysthumb and prostrate knotweed (in New York) were reduced by 71% to 99%. Except for the low rate of sulfentrazone, all herbicide treatments reduced weed biomass at harvest by ≥88%. Crop injury varied in response to herbicide treatments or weed competition but was also affected by crop and location. Between 14 and 28 DAP, the greatest amount of stunting (22%) was noted in the S-metolachlor fb oxyfluorfen treatments at both locations. Averaged over treatments, greater stunting was observed in broccoli than in cabbage in New York, whereas stunting estimates were higher for cabbage in New Jersey. All treatments in New Jersey resulted in significantly increased cabbage yield and broccoli and cabbage head sizes relative to the nontreated controls. No yield difference was noted between herbicide treatments and the nontreated check in New York. Data derived from these studies will be used to enhance crop safety recommendations in northeastern U.S. production environments for sulfentrazone used PRE in transplanted cabbage and support a potential label for broccoli.

Data from a national survey of 348 U.S. sports field managers were used to examine the effects of participation in Cooperative Extension events on the adoption of turfgrass weed management practices. Of the respondents, 94% had attended at least one event in the previous 3 yr. Of this 94%, 97% reported adopting at least one practice as a result of knowledge gained at an Extension turfgrass event. Half of the respondents had adopted four or more practices; a third adopted five or more practices. Nonchemical, cultural practices were the most-adopted practices (65% of respondents). Multiple regression analysis was used to examine factors explaining practice adoption and Extension event attendance. Compared to attending one event, attending three events increased total adoption by an average of one practice. Attending four or more events increased total adoption by two practices. Attending four or more events (compared to one event) increased the odds of adopting six individual practices by 3- to 6-fold, depending on the practice. This suggests that practice adoption could be enhanced by encouraging repeat attendance among past Extension event attendees. Manager experience was a statistically significant predictor of the number of Extension events attended but a poor direct predictor of practice adoption. Experience does not appear to increase adoption directly, but indirectly, via its impact on Extension event attendance. In addition to questions about weed management generally, the survey asked questions specifically about annual bluegrass management. Respondents were asked to rank seven sources of information for their helpfulness in managing annual bluegrass. There was no single dominant information source, but Extension was ranked more than any other source as the most helpful (by 22% of the respondents) and was ranked among the top three by 53%, closely behind field representative/local distributor sources at 54%.

Few published studies exist documenting banana pepper tolerance to clomazone. Therefore, field trials were conducted in 2022 at two Indiana locations [Meigs Horticulture Research Farm and the Pinney Purdue Agricultural Center (PPAC)] to evaluate crop safety in plasticulture-grown banana pepper. The experimental design was a split-plot in which the main plot factor was the clomazone rate (0, 840, and 1,680 g ai ha–1) and the subplot factor was cultivar (‘Pageant’ and ‘Sweet Sunset’). Clomazone was applied over the top of black polyethylene mulch-covered raised beds and their respective bare-ground row middles 1 d prior to transplanting 12 pepper plants per subplot. Data collected included crop injury on a scale from 0% (no injury) to 100% (crop death) at 2, 4, and 6 wk after treatment (WAT), and plant stand. Two harvests were performed in which mature fruits were counted and weighed. Injury presented as interveinal bleaching only at PPAC 2 and 4 WAT. At this location 1,680 g ha–1 clomazone resulted in greater injury to ‘Sweet Sunset’ at 2 and 4 WAT (53% and 15%, respectively) than to ‘Pageant’ (19% and 3%, respectively); however, plant stand and yield were not affected by either clomazone rate. These results suggest that the clomazone rate range currently used for bell pepper (280 to 1,120 g ai ha–1) can be applied prior to transplanting plasticulture-grown banana pepper with minimal crop injury and without reducing yield.