North Carolina growers have long struggled to control Italian ryegrass, and recent research has confirmed that some Italian ryegrass biotypes have become resistant to nicosulfuron, glyphosate, clethodim, and paraquat. Integrating alternative management strategies is crucial to effectively control such biotypes. The objectives of this study were to evaluate Italian ryegrass control with cover crops and fall-applied residual herbicides and investigate cover crop injury from residual herbicides. This study was conducted during the fall/winter of 2021–22 in Salisbury, NC, and fall/winter of 2021–22 and 2022–23 in Clayton, NC. The study was designed as a 3 × 5 split-plot in which the main plot consisted of three cover crop treatments (no-cover, cereal rye at 80 kg ha−1, and crimson clover at 18 kg ha−1), and the subplots consisted of five residual herbicide treatments (S-metolachlor, flumioxazin, metribuzin, pyroxasulfone, and nontreated). In the 2021–22 season at Clayton, metribuzin injured cereal rye and crimson clover 65% and 55%, respectively. However, metribuzin injured both cover crops ≤6% in 2022–23. Flumioxazin resulted in unacceptable crimson clover injury of 50% and 38% in 2021–22 and 2022–23 in Clayton and 40% in Salisbury, respectively. Without preemergence herbicides, cereal rye controlled Italian ryegrass by 85% and 61% at 24 wk after planting in 2021–22 and 2022–23 in Clayton and 82% in Salisbury, respectively. In 2021–22, Italian ryegrass seed production was lowest in cereal rye plots at both locations, except when it was treated with metribuzin. For example, in Salisbury, cereal rye plus metribuzin resulted in 39,324 seeds m–2, compared to ≤4,386 seeds m–2 from all other cereal rye treatments. In 2022–23, Italian ryegrass seed production in cereal rye was lower when either metribuzin or pyroxasulfone were used preemergence (2,670 and 1,299 seeds m–2, respectively) compared with cereal rye that did not receive an herbicide treatment (5,600 seeds m–2). cereal rye (Secale cereale L.) and crimson clover (Trifolium incarnatum L.)

Cotton producers need residual herbicides that can safely and practically be applied postemergence. Herbicide-coated fertilizers could allow for simultaneous application of residual herbicides and a bulk fertilizer blend. Therefore, a study was conducted in 2022 and 2023 in Fayetteville, AR, to evaluate cotton tolerance to 12 herbicide treatments coated onto a fertilizer blend and applied over cotton. Herbicides and rates evaluated included diuron at 840 g ai ha−1, florpyrauxifen-benzyl at 29 g ai ha−1, flumioxazin at 105 g ai ha−1, flumioxazin + pyroxasulfone at 70 + 90 g ai ha−1, fluridone at 168 g ai ha−1, fluometuron at 840 g ai ha−1, fomesafen at 280 g ai ha−1, pyroxasulfone at 128 g ai ha−1, saflufenacil at 66 g ai ha−1, saflufenacil + dimethenamid-P at 25 + 219 g ai ha−1, saflufenacil + pyroxasulfone at 44 + 91 g ai ha−1, and S-metolachlor at 1,388 g ai ha−1. In both years, fluridone, fluometuron, diuron, and S-metolachlor caused less than 10% injury at 7 d after treatment (DAT). Higher injury levels were observed in 2022 (19% to 30%) compared with 2023 (4% to 12%) for flumioxazin, fomesafen, saflufenacil, saflufenacil plus dimethenamid-P, and saflufenacil + pyroxasulfone. The elevated injury in one of two years was attributed to the presence of dew when the herbicide-coated fertilizer was applied. The initial injury was transient, as the cotton generally had recovered by 28 DAT for all herbicides. No differences in seed cotton yield or groundcover among the herbicide treatments occurred either year. These results highlight the potential of using several postemergence-applied, residual herbicides coated onto fertilizer that are not currently registered for over-the-top use in cotton.

This trial assessed the effect of preemergence herbicides on newly transplanted blackberries. A 2-yr field trial was initiated in 2021 and conducted at two locations in Fayetteville and Clarksville, AR. Seven treatments consisted of six preemergence herbicides (flumioxazin, mesotrione, napropamide, oryzalin, pendimethalin, and S-metolachlor) and one nontreated check. Preemergence herbicide treatments were applied to field plots of newly transplanted blackberry plugs (‘Ouachita’), using a CO2 backpack sprayer at 187 L ha−1 covering a 1-m swath, ensuring spray pattern overlap over newly planted blackberries in 2021 and reapplied in the same manner to established blackberries of the same plots in 2022. Data were collected on crop injury and plant height of blackberry plants in each plot. Yield data were collected in the second year, and fruit were analyzed for soluble solids content, pH, and average berry weight. In the first year, mesotrione and flumioxazin treatments caused injury to newly transplanted blackberries, and mesotrione-treated blackberries (58% in Fayetteville, 29% in Clarksville) did not fully recover by 84 d after treatment (DAT). Napropamide, S-metolachlor, oryzalin, and pendimethalin did not cause crop injury greater than 6% throughout the 2021 season. In the second year (2022), no crop injury was caused by any herbicide treatments. Results from these trials verify that flumioxazin, napropamide, oryzalin, and pendimethalin at the tested rates would be appropriate options for weed control in newly planted blackberries. These results corroborate regional recommendations against the use of mesotrione in first-year blackberry plantings. The findings from this trial indicate that S-metolachlor would be safe for registration for use on blackberries because of its limited effect on crop injury and blackberry yield.

There is limited information on the crop safety and weed control potential of commercially available PRE herbicides when applied under plastic mulch on various cucumber and summer squash cultivars grown in Florida. Two cucumber field trials were conducted at the Gulf Coast Research and Education Center in Wimauma, FL, in fall 2021 and spring 2022 to determine the effects of halosulfuron, pendimethalin, S-metolachlor, sulfentrazone, fomesafen, napropamide, oxyfluorfen, and flumioxazin on crop growth and development, yield, and the control of various weed species in the fields. We conducted this trial using three cucumber cultivars: ‘Speedway’, ‘Dominator’, and ‘Mongoose’. Two summer squash field trials were conducted simultaneously, evaluating all the mentioned herbicides, except flumioxazin, in addition to rimsulfuron on three summer squash cultivars: ‘Spineless Beauty’, ‘Payload’, and ‘Everglade’. In the cucumber trials, crop damage varied with cultivar and ranged from 3% to 16% in fall 2021. All herbicides caused ≥10% crop injury, except oxyfluorfen and flumioxazin, at 28 d after transplanting (DATr) in spring 2022. In the summer squash trial, halosulfuron, S-metolachor, and flumioxazin were the three most injurious PRE herbicides, causing more than 10% crop injury in seed-grown summer squash, with no effect of PRE herbicides on crop injury in transplant-grown summer squash in fall 2021. In spring 2022, crop injury with PRE herbicides varied with cultivar, where pendimethalin and S-metolachlor were consistently the most injurious PRE herbicides, causing 14% to 25% injury at 28 DATr. All PRE herbicides caused some damage to cucumber and summer squash, with limited differences between cultivars and no effect on overall crop yield.

An experiment was conducted in 2022 and 2023 near Rocky Mount and Clayton, NC, to evaluate residual herbicide-coated fertilizer for cotton tolerance and Palmer amaranth control. Treatments included acetochlor, atrazine, dimethenamid-P, diuron, flumioxazin, fluometuron, fluridone, fomesafen, linuron, metribuzin, pendimethalin, pyroxasulfone, pyroxasulfone + carfentrazone, S-metolachlor, and sulfentrazone. Each herbicide was individually coated on granular ammonium sulfate (AMS) and top-dressed at 321 kg ha−1 (67 kg N ha−1) onto 5- to 7-leaf cotton. The check plots received the equivalent rate of nonherbicide-treated AMS. Before top-dress, all plots (including the check) were treated with glyphosate and glufosinate to control previously emerged weeds. All herbicides except metribuzin resulted in transient cotton injury. Cotton response to metribuzin varied by year and location. In 2022, metribuzin caused 11% to 39% and 8% to 17% injury at the Clayton and Rocky Mount locations, respectively. In 2023, metribuzin caused 13% to 32% injury at Clayton and 73% to 84% injury at Rocky Mount. Pyroxasulfone (91%), pyroxasulfone + carfentrazone (89%), fomesafen (87%), fluridone (86%), flumioxazin (86%), and atrazine (85%) controlled Palmer amaranth ≥85%. Pendimethalin and fluometuron were the least effective treatments, resulting in 58% and 62% control, respectively. As anticipated, early season metribuzin injury translated into yield loss; plots treated with metribuzin yielded 640 kg ha−1 and were comparable to yields after linuron (790 kg ha−1) was used. These findings suggest that with the exception of metribuzin, residual herbicides coated onto AMS may be suitable and effective in cotton production, providing growers with additional modes of action for late-season control of multiple herbicide–resistant Palmer amaranth.

With Palmer amaranth and waterhemp evolving resistance to nine and six different sites of action (SOAs) globally, soybean producers continue to search for new options to control these problematic weeds. Bayer CropScience has announced its intentions to launch a Convintro™ brand of herbicides, one being a three-way premixture for preemergence use in soybean. The premixture will contain diflufenican (WSSA Group 12), metribuzin (WSSA Group 5), and flufenacet (WSSA Group 15), adding a new SOA for soybean producers throughout the United States. With the anticipated launch of the premixture, research is needed to evaluate the length of residual control provided by the new herbicide. Research trials were conducted in Fayetteville and Keiser, AR, and Morrice, MI, in 2022 and 2023. A 0.17:0.35:0.48 ratio of a diflufenican:metribuzin:flufenacet (DFF)-containing premixture was applied alone and in combination with additional metribuzin and dicamba. Also, metribuzin, acetochlor, a S-metolachlor:metribuzin premixture, and a flumioxazin:pyroxasulfone:metribuzin premixture were applied preemergence. The DFF-containing premixture was more effective in reducing Palmer amaranth/waterhemp emergence than acetochlor in four of six trials at 28 d after treatment (DAT). Palmer amaranth and waterhemp densities in plots treated with the DFF-containing premixture exhibited similar results to plots treated with the S-metolachlor:metribuzin premixture and the flumioxazin:pyroxasulfone:metribuzin premixture at 28 DAT. By 56 DAT, Palmer amaranth and waterhemp densities were comparable or superior in plots with the DFF-containing premixture than in those treated with acetochlor and metribuzin, and the S-metolachlor:metribuzin premixture at five of six sites. The addition of dicamba or metribuzin to the DFF-containing premixture did not reduce Palmer amaranth or waterhemp density compared to the DFF-containing premixture at 28 or 56 DAT. Overall, the DFF-containing premixture generally provided greater or comparable control over several standard herbicides, providing growers a new product for preemergence control of Amaranthus species in soybean fields.

Benghal dayflower and sicklepod are weeds of economic importance in peanut in the southeastern United States due to their extended emergence pattern and limited effective herbicides for control. Field studies were conducted near Jay, Florida, in 2022 and 2023, to evaluate the effect of planting date and herbicide combinations on Benghal dayflower and sicklepod control in peanut crops. Peanut planted in June was exposed to a higher Benghal dayflower density than peanut planted in May. Sicklepod density was similar between May and June planting dates at 28 d after preemergence and early postemergence herbicide applications, but density was greater in peanut that was planted in June, 28 d after the mid-postemergence application. A preemeergence herbicide application followed by (fb) an early postemergence application of S-metolachlor or diclosulam + S-metolachlor controlled Benghal dayflower 84% to 93% 28 d after early postemergence in peanut that was planted in May, but control was reduced to 58% to 78% in the crop that had been planted in June. Regardless of planting date, a preemeergence application fb S-metolachlor or diclosulam + S-metolachlor applied early postemergence provided <80% sicklepod control 28 d after early postemergence. Imazapic + dimethenamid-P + 2,4-DB applied postemergence improved Benghal dayflower control to at least 94% 28 d after mid-postemergence, but sicklepod control was not >85%. Regardless of the planting date, paraquat + bentazon + S-metolachlor applied early postemergence was required to achieve ≥95% sicklepod control. However, herbicide combinations that included paraquat + bentazon + S-metolachlor reduced peanut yield when planting was delayed to June. In fields that are infested with Benghal dayflower and sicklepod, it is recommended that peanut be planted in early May to minimize the potential impact of these weeds and to increase peanut yield. Late-planted peanut required more intensive herbicide applications to obtain the same peanut yield as the May-planted peanut.

Amaranthus species are problematic weeds in snap bean production systems. They reduce crop yields, and their stem fragments contaminate harvested pods. Knowledge of snap bean tolerance to different preemergence herbicides is limited; however, knowing this tolerance is essential for planning a reliable weed management system, breeding herbicide-tolerant cultivars, and registering herbicides for use on minor crops such as snap bean. Field trials were conducted in 2021 and 2022 to determine the tolerance of eight snap bean cultivars to preemergence herbicides with activity on Amaranthus species, including dimethenamid-P, flumioxazin, lactofen, metribuzin, saflufenacil, and sulfentrazone. Snap bean plant density (number of plants per square meter), plant biomass (grams per plant), and canopy biomass (grams per square meter) 21 d after treatment were used to assess crop tolerance to a range of herbicide rates. Linear mixed-effects regression models were fitted to quantify the relationships between preemergence herbicide rate and snap bean cultivar tolerance. Results indicated a high margin of crop safety with dimethenamid-P and lactofen for weed control in snap bean, and a low margin of crop safety with metribuzin and saflufenacil. Results indicated differential cultivar tolerance to flumioxazin and sulfentrazone, which could be driven by genetic variability among cultivars.

Cereal rye (Secale cereale L.) cover crop and preemergence herbicides are important components of an integrated weed management program for waterhemp [Amaranthus tuberculatus (Moq.) Sauer] and Palmer amaranth (Amaranthus palmeri S. Watson) management in soybean [Glycine max (L.) Merr.]. Accumulating adequate cereal rye biomass for effective suppression of Amaranthus spp. can be challenging in the upper Midwest due to the short window for cereal rye growth in a corn–soybean rotation. Farmers are adopting the planting green system to optimize cereal rye biomass production and weed suppression. This study aimed to evaluate the feasibility of planting soybean green when integrated with preemergence herbicides for the control of Amaranthus spp. under two soybean planting time frames. The study was conducted across 19 site-years in the United States over the 2021 and 2022 growing seasons. Factors included cover crop management practices (“no-till,” “cereal rye early-term,” and “cereal rye plant-green”), soybean planting times (“early” and “late”), and use of preemergence herbicides (“NO PRE” and “YES PRE”). Planting soybean green increased cereal rye biomass production by 33% compared with early termination. Greater cereal rye biomass production when planting green provided a 44% reduction in Amaranthus spp. density compared with no-till. The use of preemergence herbicides also resulted in a 68% reduction in Amaranthus spp. density compared with NO PRE. Greater cereal rye biomass produced when planting green reduced soybean stand, which directly reduced soybean yield in some site-years. Planting soybean green is a feasible management practice to optimize cereal rye biomass production, which, combined with preemergence herbicides, provided effective Amaranthus spp. management. Soybean stand was a key factor in maintaining soybean yields compared with no-till when planting green. Farmers should follow best management recommendations for proper planter and equipment setup to ensure effective soybean establishment under high levels of cereal rye biomass when planting green.

Flumioxazin and S-metolachlor are widely used in conventional sweetpotato production in North Carolina and other states; however, some growers have recently expressed concerns about potential effects of these herbicides on sweetpotato yield and quality. Previous research indicates that activated charcoal has the potential to reduce herbicide injury. Field studies were conducted in 2021 and 2022 to determine whether flumioxazin applied preplant and S-metolachlor applied before and after transplanting negatively affect sweetpotato yield and quality when activated charcoal is applied with transplant water. The studies evaluated five herbicide treatments and two activated charcoal treatments. Herbicide treatments included two flumioxazin rates, one S-metolachlor rate applied immediately before and immediately after transplanting, and no herbicide. Charcoal treatments consisted of activated charcoal applied at 9 kg ha−1, and no charcoal. No visual injury from herbicides or charcoal was observed. Likewise, no effect of herbicide or charcoal treatment on no. 1, marketable (sum of no. 1 and jumbo grades), or total yield (sum of canner, no. 1, and jumbo grades) was observed. Additionally, shape analysis conducted on calculated length-to-width ratio (LWR) for no. 1 sweetpotato roots found no effect from flumioxazin at either rate on sweetpotato root shape. However, both S-metolachlor treatments resulted in lower LWR of no. 1 sweetpotato roots in 2021. Results are consistent with prior research and indicate that flumioxazin and S-metolachlor are safe for continued use on sweetpotato at registered rates.

Sicklepod is one of the most difficult to control weeds in peanut production in the southeastern United States due to its extended emergence pattern and limited effective herbicides for control. Growers rely on preemergence herbicides as the foundation of their weed control programs; however, postemergence herbicides are often needed for season-long weed control. The objectives of this study were to evaluate the effect of planting pattern and herbicide combinations for sicklepod control in peanut crops. Due to rapid canopy closure, twin-row planting improved late-season sicklepod control by 13% and peanut yield by 5% compared with a single-row pattern. A preemergence application of fluridone, flumioxazin, or fluridone + flumioxazin provided 76% to 89% control of sicklepod 28 d after preemergence. Regardless of the herbicide applied preemergence, paraquat + bentazon + S-metolachlor applied early postemergence was required to achieve ≥90% sicklepod control 28 d after early postemergence. All preemergence herbicide treatments followed by (fb) S-metolachlor or diclosulam + S-metolachlor applied early postemergence provided <90% control 28 d after early postemergence. A mid-postemergence application of imazapic + dimethenamid-P + 2,4-DB controlled sicklepod by 67% to 79% prior to peanut harvest, and biomass reduction was unacceptable (<80%), resulting in difficulty in peanut digging. The highest peanut yield was observed when paraquat + bentazon + S-metolachlor was applied early postemergence fb imazapic + dimethenamid-P + 2,4-DB applied mid-postemergence. Based on the results of this study, a herbicide combination of paraquat + bentazon + S-metolachlor is an important early-season tool for controlling sicklepod in peanut crops. The results also showed that a twin-row planting pattern improved late-season sicklepod control but did not reduce herbicide input to protect peanut yield.

Downy brome is a cleistogamous facultative winter-annual grass weed that invades cropland, pastureland, and ruderal areas in western North America. Glyphosate-resistant downy brome, the first known glyphosate-resistant grass weed in Canada, was confirmed in a glyphosate-resistant canola field in southern Alberta in 2021. A controlled-environment study was conducted to determine the impact of preemergence soil-applied residual herbicides on glyphosate-resistant and susceptible downy brome in two field soils. Flumioxazin/pyroxasulfone (70/89 g ai ha−1), carfentrazone/pyroxasulfone (18/150 g ai ha−1), sulfentrazone/pyroxasulfone (100/100 or 150/150 g ai ha−1), and saflufenacil/pyroxasulfone (36/120 g ai ha−1) resulted in excellent (≥90%) visible control and downy brome biomass reduction 8 wk after treatment (WAT). The low rate of carfentrazone/pyroxasulfone (12/100 g ai ha−1) resulted in good (≥80%) visible control and biomass reduction 8 WAT, while the low and medium rates of saflufenacil/pyroxasulfone (18/60 or 25/84 g ai ha−1) resulted in ≥80% biomass reduction but suppression only (66% to 75%) based on visible control. Flumioxazin alone (105 g ai ha−1) resulted in good visible control (81%) 8 WAT in a sandy loam soil, but poor (13%) control in a clay loam soil. Soil type affected plant growth as evidenced by reduced growth in the untreated sandy loam soil compared to clay loam soil. The glyphosate-resistant population emerged and grew more vigorously than the glyphosate-susceptible population resulting in greater plant densities in the untreated control and some less-effective herbicide treatments. These results suggest that mixtures of a protoporphyrinogen oxidase-inhibiting herbicide with the very-long-chain fatty acid elongase inhibitor pyroxasulfone applied preemergence at ≥89 g ai ha−1 could be effective components of an herbicide layering strategy targeting glyphosate-resistant and glyphosate-susceptible downy brome.

Waterhemp has evolved resistance to Group 2, 5, 9, 14, and 27 herbicides in Ontario, Canada, making control of this challenging weed even more difficult. Acetochlor is a Group 15, chloroacetanilide herbicide that has activity on many small-seeded annual grasses and some small-seeded annual broadleaf weeds, including waterhemp. The objective of this study was to ascertain if acetochlor mixtures with broadleaf herbicides (dicamba, metribuzin, diflufenican, sulfentrazone, or flumioxazin), applied preemergence (PRE), increase multiple-herbicide-resistant (MHR) waterhemp control in soybean. Five trials were conducted over 2 yr (2021 and 2022). The acetochlor mixtures caused ≤7% soybean injury, except acetochlor + flumioxazin, which caused 19% soybean injury. Acetochlor applied PRE controlled MHR waterhemp 89% at 4 wk after application (WAA). Dicamba, metribuzin, diflufenican, sulfentrazone, or flumioxazin controlled MHR waterhemp 59%, 67%, 58%, 64%, and 86%, respectively, at 4 WAA. Acetochlor applied in a mixture with dicamba, metribuzin, diflufenican, sulfentrazone, or flumioxazin provided good to excellent control of MHR waterhemp; control ranged from 91% to 98% but was similar to acetochlor applied alone. Acetochlor alone reduced MHR waterhemp density and biomass 98% and 93%; acetochlor + flumioxazin reduced waterhemp density and biomass by an additional 2% and 7%, respectively. This research concludes that acetochlor applied in a mixture with flumioxazin was the most efficacious mixture evaluated for MHR waterhemp control.

Herbicides that inhibit protoporphyrinogen oxidase (PPO) are used in more than 40 agronomic and specialty crops across Georgia to manage weeds through residual and postemergence (POST) control. In 2017, a population of Palmer amaranth exhibiting reduced sensitivity to POST applications of PPO-inhibiting herbicides was identified by the University of Georgia. Seed were collected from the site along with a known sensitive population; distance between the samples was 200 m, increasing the likelihood of similar environmental and genetic characteristics. To quantify sensitivity for both preemergence (PRE) and POST uses, 21 greenhouse dose-response assessments were conducted from 2017 to 2022. After conducting initial rate-response studies, 13 doses per herbicide were chosen for the POST experiment; field use rates of fomesafen (420 g ai ha−1), lactofen (219 g ai ha−1), acifluorfen (420 g ai ha−1), and trifludimoxazin (25 g ai ha−1) ranging from 0× to 4× the field use rate for the susceptible population, and 0× to 40× for the suspect population were applied. Herbicide treatments included adjuvants and were applied to plants 8 to 10 cm in height. Relative resistance factors (RRFs) were calculated for control ratings, mortality, and biomass, and ranged from 105 to 318, 36 to 1,477, 215 to 316, and 9 to 49 for fomesafen, lactofen, acifluorfen, and trifludimoxazin, respectively. In the PRE experiment, herbicide applications included five to nine doses of fomesafen (1× = 210 g ai ha−1), flumioxazin (1× = 57 g ai ha−1), oxyfluorfen (1× = 561 g ai ha−1), and trifludimoxazin (1× = 38 g ai ha−1); doses ranged from 0× to 6× for the suspect population and 0× to 2× for the susceptible population. Visual control, mortality, and biomass RRFs ranged from 3 to 5 for fomesafen, 21 to 31 for flumioxazin, 6 to 22 for oxyfluorfen, and 8 to 38 for trifludimoxazin. Results confirm that a Georgia Palmer amaranth population is resistant to PPO-inhibiting herbicides applied both PRE and POST.

Preemergence applications of mesotrione, an herbicide that inhibits 4-hydroxyphenolpyruvate dioxygenase (HPPD), have recently gained regulatory approval in soybean varieties with appropriate traits. Giant ragweed is an extremely competitive broadleaf weed, and biotypes resistant to acetolactate synthase inhibitors (ALS-R) can be particularly difficult to manage with soil-residual herbicides in soybean production. This study investigated control of giant ragweed from preemergence applications of cloransulam (32 g ai ha–1), metribuzin (315 g ai ha–1), and S-metolachlor (1,600 g ai ha–1) in a factorial design with and without mesotrione (177 g ai ha–1) at two different sites over 2 yr. Treatments with mesotrione were also compared with two commercial premix products: sulfentrazone (283 g ai ha–1) and cloransulam (37 g ai ha–1), and chlorimuron (19 g ai ha–1), flumioxazin (69 g ai ha–1), and pyroxasulfone (87 g ai ha–1). At 42 d after planting, control and biomass reduction of giant ragweed were greater in treatments with mesotrione than any treatment without mesotrione. Giant ragweed biomass was reduced by 84% in treatments with mesotrione, whereas treatments without mesotrione did not reduce biomass relative to the nontreated. Following these preemergence applications, sequential herbicide treatments utilizing postemergence applications of glufosinate (655 g ai ha–1) plus fomesafen (266 g ai ha–1) and S-metolachlor (1,217 g ai ha–1) resulted in at least 97% control of giant ragweed at 42 d after planting, which was greater than sequential applications of glufosinate alone in 3 of 4 site-years. Preemergence applications of mesotrione can be an impactful addition to soybean herbicide programs designed to manage giant ragweed, with the potential to improve weed control and delay the onset of herbicide resistance by providing an additional effective herbicide site of action.

Glyphosate-resistant (GR) horseweed is a problematic weed for Michigan soybean growers. Additionally, rosette- and upright-horseweed growth types have been observed co-emerging during mid- to late summer in several Michigan fields. In the greenhouse, shade levels from 35% to 92% reduced rosette- and upright-horseweed biomass 31% to 99% compared with the upright growth type grown under 0% shade. Greater reductions in biomass occurred under 69% and 92% shade. Thus, increased shading by planting in narrow rows and/or planting green into cereal rye may improve horseweed suppression. A field experiment conducted over 3 site-years compared the effect of fall-planted cereal rye terminated with glyphosate 1 wk after planting (WAP; planting green) with a preemergence residual herbicide program (glyphosate + 2,4-D + flumioxazin + metribuzin) on horseweed control in soybean planted in three row widths (19, 38, and 76 cm). Planting green or applying a residual herbicide program across all row widths reduced horseweed biomass 86% to 91% and 95% to 99%, respectively, compared with soybean planted with no cover in 76-cm rows, 4 to 6 WAP. At soybean harvest, when a noneffective postemergence herbicide (glyphosate) was applied, horseweed biomass was 42% and 81% lower by planting green or applying a residual-herbicide program compared with no cover, respectively. Similarly, planting soybean in 19-cm rows reduced horseweed biomass compared with 38- and 76-cm rows. When an effective postemergence program was applied, similar horseweed biomass reductions were observed by planting green or applying a residual herbicide across all row widths. Additionally, soybean yield and economic returns were similar between planting green and applying a residual herbicide in 1 of 2 site-years. Integrating planting green and an effective postemergence herbicide program offers an alternative horseweed management strategy to applying a residual preemergence herbicide program.

Winter annual weeds begin to germinate as zoysiagrass enters winter dormancy in autumn. These weeds can suppress zoysiagrass shoot development the following spring through competition for sunlight, moisture, and nutrients. Previous research involving winter annual weed control in dormant turfgrass has been conducted primarily on bermudagrass, but less is known about how various herbicides used for this purpose will influence zoysiagrass after dormancy transition. Two field studies were conducted over 7 site-years between 2016 and 2020 to evaluate 17 herbicide treatments that are typically marketed for broadleaf weed control in spring and 18 herbicide treatments that are typically marketed for annual bluegrass control during winter for their effects on a variety of weeds and semidormant ‘Meyer’ and dormant ‘Zeon’ zoysiagrass, respectively. Glufosinate, glyphosate + simazine, and indaziflam + simazine controlled Persian speedwell by more than 90% and control was significantly greater with auxin-type and other herbicide combinations. Dandelion and Persian speedwell were better controlled with a combination of simazine and glyphosate than when glyphosate was applied alone. Glufosinate controlled dandelion, hairy bittercress, and Persian speedwell more effectively than glyphosate. In Meyer zoysiagrass, glyphosate and glufosinate controlled annual bluegrass equivalently, whereas in Zeon zoysiagrass, glyphosate controlled annual bluegrass better than glufosinate did. Foramsulfuron or treatments that contained simazine resulted in >90% control of annual bluegrass. A flumioxazin admixture with diquat, glufosinate, or glyphosate improved annual bluegrass control. Herbicide treatments that contain diquat, glufosinate, glyphosate, and metsulfuron alone or in a tank-mix should not be applied to Meyer zoysiagrass with 5% visual green turf cover due to high injury potential. In both studies, glufosinate was more injurious to Meyer and Zeon zoysiagrass than glyphosate. Overall, several herbicides that control annual bluegrass or broadleaf weeds can be safely applied to Zeon zoysiagrass during dormancy or Meyer zoysiagrass during post-dormancy transition.

Control of southern pine species that easily establish from seed, such as loblolly pine and slash pine (wilding pines), has historically been achieved economically through the use of prescribed fire or application of glyphosate or glyphosate and saflufenacil during site preparation. Currently, alternatives to glyphosate are being investigated for wilding pine control because of health and safety concerns over glyphosate reported by some organizations. Two exploratory studies in the Coastal Plain Region of Georgia investigated the potential of several herbicides for wilding pine control with 0.56 to 0.70 kg ha−1 of 0.9-kg ae imazapyr included in all herbicide treatments. Application timings for Study 1 were July and September (n = 8 treatments per timing), whereas Study 2 took place in July and early November (n = 4 treatments per timing). In Study 1, various rates of choline triclopyr, ester triclopyr, fluroxypyr, aminopyralid + florpyrauxifen-benzyl, and aminopyralid + triclopyr were tested, while two treatments contained glyphosate. Study 2 investigated mixtures containing flumioxazin, glufosinate, and triclopyr. Results for Study 1 revealed that the two treatments containing glyphosate had the greatest percent loblolly pine control after 120 d (87.5% and 88.6% control, respectively), while the next best control was offered by a treatment containing imazapyr plus 3.36 kg ha−1 choline triclopyr (52.6% control). July treatments offered better control than September treatments, but the efficacy of September treatments may have been impacted by a severe drought. In Study 2, treatments applied during early November that contained imazapyr and glufosinate or imazapyr, glufosinate, and flumioxazin resulted in 100% control of mixed loblolly and slash pine seedlings and saplings. All November treatments offered better control than July treatments in Study 2. Promising results from Study 2 suggest that glufosinate may warrant additional study for use in forestry site preparation as an alternative to glyphosate to control wilding pines.

The tolerance of cereal rye to eight herbicides registered for use in wheat, at two rates, was evaluated for potential labeling in cereal rye to expand limited chemical weed control options. Across five site-years, halauxifen-methyl + florasulam, pyroxsulam, and thifensulfuron-methyl + tribenuron-methyl applied at a 2X rate to cereal rye at Zadoks (Z) 13 caused less than 15% injury and had no impact on cereal rye density. These herbicides at the 2X rate reduced cereal rye heights 11% at 10 days after treatment (DAT), with rye recovering by 31 DAT; cereal rye heights were not reduced with these herbicides at their 1X rate. In contrast, significant injury was observed with the 1X rate of mesosulfuron-methyl (45%), pinoxaden (27%), and pinoxaden + fenoxaprop-P-ethyl (30%) applied postemergence; early-season height was reduced 19% to 26%. Residual herbicide pyroxasulfone applied as a delayed preemergence at Z 10 and flumioxazin + pyroxasulfone applied at Z 11 caused 27% to 28% and 16% to 47% injury, respectively, when the 1X rate was activated by rainfall within 2 d of application. These residual herbicides reduced cereal rye height and density up to 35% and 40%, respectively. Cereal rye grain yield was not influenced by herbicide or rate applied.

Six field experiments were conducted to investigate any interaction between pyroxasulfone and flumioxazin on soybean tolerance and control of multiple-herbicide-resistant (MHR) waterhemp in soybean during 2016 and 2017 in Ontario, Canada. There was a synergistic increase in soybean injury with the co-application of pyroxasulfone and flumioxazin at all rates evaluated at 2 wk after emergence (WAE), the two highest rates evaluated (134/106 and 268/211 g ai ha–1) at 4 WAE, and the highest rate (268/211 g ai ha–1) evaluated at 8 WAE. Soybean injury with all pyroxasulfone and flumioxazin treatments was transient and had no adverse effect on soybean grain yield. Pyroxasulfone applied preemergence at 45, 89, 134, and 268 g ai ha–1 controlled MHR waterhemp up to 72%, 89%, 92%, and 95%, respectively. Flumioxazin applied preemergence at 35, 70, 106, and 211 g ai ha–1 controlled MHR waterhemp up to 78%, 90%, 93%, and 96%, respectively. Pyroxasulfone/flumioxazin applied preemergence at 45/35, 89/70, 134/106, and 268/211 g ai ha–1 controlled MHR waterhemp up to 92%, 96%, 98%, and 100%, respectively. There were no significant antagonistic or synergistic interactions for the control of MHR waterhemp with pyroxasulfone/flumioxazin at rates evaluated except at 268/211 g ai ha–1, which provided a synergistic increase in MHR waterhemp control at 4 WAE. The MHR waterhemp biomass and density reductions followed a trend similar trend to visible control. Pyroxasulfone/flumioxazin at 268/211 g ai ha–1 caused a synergistic response in biomass reduction (9% difference). Based on these results, there is an additive increase in MHR waterhemp control and potential for a synergistic increase in soybean injury with the co-application of pyroxasulfone plus flumioxazin.