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Auxin herbicide drift to susceptible soybean [Glycine max (L.) Merr.] and cotton (Gossypium hirsutum) cultivars are a significant concern. Additionally, the impact of auxin herbicide drift on pollinators' foraging sources, including soybean, needs to be understood. A field experiment was conducted in 2022 at the University of Arkansas at Pine Bluff Small Farm Outreach Center near Lonoke, Ark., to evaluate the effect of auxin herbicide simulated drift rates on soybean reproductive organs (flowers and pods), pollen grains, and grain yield. A randomized complete block design was implemented with 8 replications. Four herbicides [florpyrauxifen-benzyl (Loyant®), 2,4-D (Enlist® One), dicamba (Engenia®), and quinclorac (Facet®)] were used at 2 rates (1/100x and 1/1000x the labeled rate) except for quinclorac, applied only at 1/100x the labeled rate. Four random soybean plants were collected from each treatment at the R3 growth stage, and reproductive organs were counted. Soybean flowers were also collected for pollen quantification 1 d before anthesis, and soybean was harvested at physiological maturity. Results showed that simulated drift rates of dicamba and florpyrauxifen-benzyl decreased the total number of soybean reproductive organs, pollen grains, and grain yield compared to the untreated control. Dicamba and florpyrauxifen-benzyl applied at 1/100x of the labeled rate reduced the number of reproductive organs by 35% and 39% at R3 compared to the nontreated control. Dicamba and florpyrauxifen-benzyl applied at this rate decreased pollen grains produced per anther by 28% and 18%, respectively, compared to the nontreated control. Applications of dicamba and florpyrauxifen-benzyl at 1/100x of the labeled rate reduced soybean grain yield by 43% and 27%, respectively, compared to the nontreated control. In addition to grain yield reduction, these results show that simulated auxin herbicide drift rates negatively impact pollinators' foraging sources with decreased pollen grain production and reducing the total number of reproductive organs, further illustrating the need for drift mitigation strategies to be developed and implemented. [ABSTRACT FROM AUTHOR]

Reviton® (tiafenacil) is a new protoporphyrinogen oxidase (PPO)-inhibiting herbicide labeled for burndown applications. However, as burndown applications can be stretched across a wide range of dates in the mid-South, there is an increased potential for off-target movement onto emerged crops. As a result, research was needed to determine the effects of simulated drift rates of Reviton on soybean [Glycine max (L.) Merr.]. In 2022, an experiment was established in Newport, Ark., St. Joseph, La., Alexandria, La., and Milan, Tenn., to assess the tolerance of soybean to simulated drift rates of Reviton herbicide when exposed at the V2 soybean growth stage. Reviton simulated drift rates of 1/8, 1/16, 1/32, 1/64, 1/128, and 1/256 of the labeled rate (1 fl oz./ac) were applied to determine the potential consequences of off-target movement. The higher simulated drift rates of Reviton (1/8x and 1/16x) caused greater visual injury (greater than 60% 2 weeks after application), height reduction (approximately 36% reduction 4 weeks after application), and yield reduction (55% and 26% reduction for the 1/8x and 1/16x rates, respectively) compared to other rates. These results suggest soybean growers should be concerned about Reviton drift onto their soybean crop, and appropriate measures should be taken to reduce off-target movement of Reviton to avoid soybean growth and yield reductions. [ABSTRACT FROM AUTHOR]

Yellow nutsedge (Cyperus esculentus) has the capability of competing with cotton throughout the season, causing a yield reduction of 34%. Envoke gives another option in a cotton production system for controlling problematic weeds such as morningglories and yellow nutsedge. Two studies were conducted in 2022 at Tillar, Ark., in a Herbert silt loam soil with the objective of evaluating Envoke rates and tank mixtures when applied postemergence in Enlist and XtendFlex cotton systems. Trials were arranged in a randomized complete block design with four replications. Herbicides used included individual and combinations of Envoke at 0.075 and 0.125 oz/ac, Enlist One at 32 oz/ac, Engenia at 12.8 oz/ac, Roundup PowerMax 3 at 30 oz/ac, Dual Magnum at 16 oz/ac, and Warrant at 64 oz/ac. All data were analyzed using JMP Pro 17 and subjected to analysis of variance using Tukey's honestly significant difference (a = 0.05). The higher rate of Envoke generally resulted in greater injury, especially when combined with Roundup PowerMax and either Enlist One or Engenia at 21 days after treatment (DAT) compared to the lower rate. No control of Palmer amaranth was observed by Envoke due to it being an acetolactate synthase-resistant population. Palmer amaranth control was not decreased due to the tank mixture of Envoke with either Enlist One or Engenia. The use of Envoke in a tank mixture with either Enlist One or Engenia will provide an alternative to yellow nutsedge control in both Enlist and XtendFlex systems. [ABSTRACT FROM AUTHOR]

Field experiments were conducted in 2022 at the University of Arkansas Pine Bluff Small Farm Outreach Center near Lonoke, Ark., to evaluate the impact of coating fertilizer with herbicides on weed control efficacy. The first study used three herbicide programs [florpyrauxifen-benzyl (Loyant), a premixture of florpyrauxifen-benzyl + penoxsulam (Novixid), and a mixture of halosulfuron (Permit) + florpyrauxifen-benzyl (Loyant)] applied either as directly coated on urea or as a foliar spray application following urea application, leading to a total of six treatments. Urea (46%), Loyant, Novixid, and Permit were applied at 68.96, 0.03, 0.06, and 0.01 lb ai/ac, respectively. A nontreated control that received an application of urea was also included for weed control evaluation purposes. In a second study, the effect of coating urea with the 4-hydroxyphenylpyruvate dioxygenase-(HPPD-) inhibiting herbicide benzobicyclon (Rogue) was evaluated for weed control. Benzobicyclon sprayed versus coated on urea was applied preflood, flood or post-flood (2 weeks after flood treatment) at 0.34 lb ai/ac. In the first study, barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.], rice flatsedge (Cyperus iria L.), and yellow nutsedge (Cyperus esculentus L.) control were affected by treatments at 7, 14, and 22 days after application (DAA), while hemp sesbania [Sesbania herbacea (Mill.) McVaugh] control was affected only at 7 DAA. In most cases, Novixid sprayed foliarly and Novixid-coated urea provided near similar levels of control of barnyardgrass, rice flatsedge, yellow nutsedge, and hemp sesbania. In the second study, hemp sesbania and sprangletop (Diplachne spp) control were numerically improved with Rogue applied at flood compared to the other application timings. Also, Rogue-coated on urea at flood provided numerically greater control of both weeds, 15 and 29 days after flood, than did the herbicide when sprayed. As a result, Novixid-coated and Rogue-coated fertilizers may be viable options to maintain high levels of weed control on some of the most problematic Arkansas rice weeds while mitigating off-target herbicide movement. [ABSTRACT FROM AUTHOR]

Reviton (tiafenacil) is a new protoporphyrinogen oxidase (PPO)-inhibiting herbicide labeled for burndown applications. However, as burndown applications can be stretched across a wide range of dates in the Mid-South, there can be a high potential for off-target movement to occur onto emerged crops. As a result, research was needed to determine the effects of simulated drift rates of Reviton to rice (Oryza sativa L.). In 2022, an experiment was established in Lonoke, Arkansas, St. Joseph, Louisiana, and Stoneville, Mississippi, to assess the tolerance of rice to simulated drift rates of Reviton herbicide at two exposure timings. Reviton simulated drift rates of 1/8, 1/16, 1/32, 1/64, 1/128, and 1/256 of the labeled rate (1 fl oz/ac) were applied to determine the potential consequences of off-target movement on rice. No height or rough rice yield differences resulted from exposure to simulated drift rates of Reviton. Reviton caused greater visual injury to rice at higher simulated drift rates (particularly 1/8 and 1/16 of the labeled rate) when exposure occurred at an early growth stage; however, rice recovered without yield reduction. This research indicates rice growers should not have major concerns about Reviton drift onto their rice crop; however, appropriate measures should always be taken to reduce off-target movement of herbicide applications. [ABSTRACT FROM AUTHOR]

Italian ryegrass [Lolium perenne L. ssp. multiflorum (Lam.) Husnot] has become more problematic and difficult to control because it is resistant to multiple herbicides. Fall-applied residual herbicides have effectively controlled other winter annual weeds and could be another option in controlling Italian ryegrass. The objective of this study was to evaluate multiple residual herbicides for the control of Italian ryegrass in the fall and the following spring before planting soybean [Glycine max (L.) Merr.]. Before any weed emergence, a field experiment was initiated at the University of Arkansas System Division of Agriculture's Jackson County Extension Center near Newport, Ark., in the fall of 2021. Treatments in this experiment consisted of Anthem® Flex (4 fl oz/ac), Command® (20 fl oz/ac), Dual Magnum® (1.33 pt/ac), Outlook® (16 fl oz/ac), Prowl® (2.1 pt/ac), Treflan® (2 pt/ac), Warrant® (2.5 pt/ac), Warrant® (5 pt/ac), and Zidua® SC (3.75 fl oz/ac). Initial visual control of Italian ryegrass 14 days after application (DAA) (28 Oct. 2021) exceeded 95% for every herbicide treatment except for Prowl and the low rate of Warrant. Only Zidua SC, Anthem Flex, and Dual Magnum retained effective residual control at 60 DAA (13 Dec. 2021) (>95%) and 166 DAA (29 March 2022) (>90%). Overall, using Zidua SC, Anthem Flex, and Dual Magnum herbicides were the most effective options to control Italian ryegrass in the fall and following spring before planting soybean. These fall-applied treatments would improve overall Italian ryegrass management and delay the evolution of resistance to postemergence herbicides. [ABSTRACT FROM AUTHOR]

Based on recent surveys, barnyardgrass [(Echinochloa crus-galli (L.) P. Beauv] and Amazon sprangletop [Diplachne panicoides (J. Presl) Hitchc.] are considered the most problematic grass weeds in Arkansas furrow-irrigated rice (Oryza sativa L.) fields. Without the benefit of established flood conditions to assist in controlling weeds, the utilization of residual herbicides throughout the season is required. In 2022, an experiment was conducted in Tillar, Ark., to determine the most effective one-shot rice herbicide tank-mixtures to control barnyardgrass and Amazon sprangletop in furrow-irrigated rice. Herbicide treatments consisted of Rebel EX, Ricebeaux, and Ricestar HT applied alone or in tank-mixture with Command or RiceOne and Ricestar HT + Postscript + Command applied at the 2-leaf rice stage. At 9 days after application (DAA), Ricebeaux in tank-mixture with RiceOne provided greater than 95% visual control of both grass species. By 17 DAA, herbicide efficacy had decreased from most herbicide treatments; however, Ricebeaux in tank-mixture with RiceOne and Ricestar HT + Postscript + Command continued to provide greater than 88% control of barnyardgrass. When applied alone, Rebel EX, Ricebeaux, and Ricestar HT failed to provide greater than 60% control of either grass species at 17 DAA. At the final evaluation, most herbicide treatments continued to decrease in control of both grasses; however, Ricestar HT + Postscript + Command provided 94% control of barnyardgrass and 91% control of Amazon sprangletop at 22 DAA. These data suggest that the use of multiple residual herbicides and modes of action will be beneficial in controlling these problematic grass weeds in furrow-irrigated rice. [ABSTRACT FROM AUTHOR]

Herbicide resistance has become increasingly problematic in production agriculture, creating a great demand for alternative control options. Field studies were conducted at the University of Arkansas System Division of Agriculture's Jackson County Extension Center near Newport, Ark. and the Rohwer Research Station near Rohwer, Ark. to evaluate postemergence (POST) herbicide tank-mixtures in an Enlist® E3 soybean [Glycine max (L.) Merr.] system. Treatments consisted of Enlist One® (2,4-D choline) alone and in combination with other products, including Roundup PowerMax® II (glyphosate), Moccasin® (S-metolachlor), Liberty® (glufosinate), and Reflex® (fomesafen). Visual estimations of weed control and soybean crop injury were collected 14 and 21 days after application (DAA) of the initial POST treatment, which was made to 4-to 6-in.ch weeds. At the Jackson County location, soybean was drilled in 7.5-in. row widths, and at the Rohwer location, soybean was planted in 38-in. row widths. Visual control of Palmer amaranth (Amaranthus palmeri S. Wats.) was 100% at Jackson County across all rating timings; however, there was more variability between treatments at the Rohwer location. These data demonstrate the capability of reduced row spacing to aid in successful weed management efforts. Results from the Rohwer location highlight the importance of combining a non-selective herbicide such as Roundup PowerMax II or Liberty with Enlist One to provide excellent control (= 90%) of barnyardgrass (Echinochloa crus-galli P. Beauv.), as well as adding an overlapping residual herbicide to the tank-mixture to provide weed control throughout the season. [ABSTRACT FROM AUTHOR]

The introduction of Xtend™ soybean [Glycine max (L.) Merr.] to the market has allowed the use of dicamba and glyphosate for postemergence weed control. Regulations in 2021 also required the addition of volatility reduction agents (VRAs) to dicamba spray mixtures. Understanding the impact of these VRAs paired with dicamba and glyphosate alone and in tank mixture on weed control, droplet size, velocity, and spray pH is essential. A field experiment was conducted in 2021 at the University of Arkansas System Division of Agriculture's Rohwer Research Station near Rohwer, Ark., to evaluate the impact of VRAs on dicamba (Engenia®) and glyphosate (Roundup PowerMax® II) spray solution pH and weed control. A laboratory experiment was conducted in 2022 at the University of Arkansas System Division of Agriculture's Lonoke County Extension Center, Lonoke, Ark., to measure the droplet size of the spray solutions evaluated in the field experiments. Adding glyphosate to dicamba decreased the pH of the solutions below 5.0. VRAs increased the pH of the spray solutions but did not affect weed control except for a minor reduction (5 percentage points) in barnyardgrass control 27 days after application (DAA). Results revealed an antagonistic interaction between dicamba and glyphosate for the control of Palmer amaranth (Amaranthus palmeri S. Wats.) 27 DAA and barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] 19 and 27 DAA. Glyphosate and dicamba in tank mixture reduced Palmer amaranth control by 14 percentage points 27 DAA compared to dicamba alone and reduced barnyardgrass control by 6% and 12% 19 and 27 DAA, respectively, compared to glyphosate alone. Across VRAs, dicamba alone produced droplets of the largest size with a Dv0.5 of 846 µm. Adding glyphosate to dicamba increased the driftable fines (droplets < 200 µm) from 1.56% to 4.13%. Across herbicides, VaporGrip® Xtra VRA produced the largest Dv0.5 of 763 µm. Spray droplet velocity was not different between VRAs when dicamba alone or in tank mixture was used. VaporGrip® Xtra VRA produced droplets with greater velocity when glyphosate alone was used. [ABSTRACT FROM AUTHOR]

In a recent survey, Amazon sprangletop [Diplachne panicoides (J. Presl) Hitchc.] and rice flatsedge (Cyperus iria L.) were among the top problematic weeds in Arkansas rice acres. Benzobicyclon, a 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting postflood herbicide, has recently been registered for use in Arkansas and has shown to provide broadspectrum control of many aquatics, broadleaf, sedge, and grass weeds in rice. Two experiments were conducted in Tillar, Arkansas, to determine an effective rate of benzobicyclon to control Amazon sprangletop and rice flatsedge at varying growth stages. Both experiments were conducted in a randomized complete block design with four replications. Herbicide treatments consisted of benzobicyclon applied at 0.109, 0.218, and 0.328 lb ai/ac and tank-mixed with methylated seed oil concentrate at 1.0% v/v. Treatments were applied to rice flatsedge at 3 to 4 in., 6 to 8 in., and 12 to 18 in. in heights and to Amazon sprangletop at the 3 to 4 leaf, tillering and heading growth stages. At 7 days after application (DAA), no rate of benzobicyclon provided greater than 64% control of rice flatsedge. Control from all rates was less than 86% at the second height (6 to 8 in.) at 21 DAA. All rates of benzobicyclon provided greater than 98% control of rice flatsedge at the smallest height (3 to 4 in.) at 41 DAA. In the second experiment, benzobicyclon at 0.218 lb ai/ac provided greater than 90% control of Amazon sprangletop when applied to the 3 to 4 leaf timing at 21 DAA. Throughout the experiment, benzobicyclon at 0.328 lb ai/ac provided greater control of Amazon sprangletop when applied at the two smallest timings. Although little control was observed from any rate of benzobicyclon when applied to heading sprangletop, benzobicyclon at the highest rate did prohibit seedhead maturation. Based on these data, the use of benzobicyclon can be beneficial in controlling these problematic weeds. [ABSTRACT FROM AUTHOR]

The control of barnyardgrass in Arkansas rice (Oryza sativa, L.) systems has plagued growers since the crop was first cultivated in the state. Now resistance to herbicides used in Arkansas production programs has complicated barnyardgrass control, and potential delays in herbicide applications due to weather events have made that control even more difficult. Two studies were conducted at the University of Arkansas at Pine Bluff Small Farm Outreach Center near Lonoke to evaluate potential salvage options for the control of barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] in Arkansas rice production. Ten herbicide treatments were applied at preflood and postflood in two separate trials. Results show that Ricestar HT alone did not control barnyardgrass in a last resort salvage situation. Ricestar HT mixed with several other herbicide options at full rates (Facet L, Regiment, Postscript, and Clincher) provided adequate control of barnyardgrass in this salvage situation when applied both preflood and postflood. Rough rice yields followed barnyardgrass control trends and demonstrated that several salvage treatment options saved yield potential. One aspect that needs to be carefully examined is whether the salvage treatment was economically feasible and whether saving yield potential was profitable to the grower. [ABSTRACT FROM AUTHOR]

Pennsylvania smartweed [Persicaria pensylvanica (L.) M. Gomez] has become increasingly more difficult to control in Arkansas rice production systems. With the repeated use of acetolactate synthase (ALS)-inhibiting herbicides as the standard for control, more stress has been put on this site-of-action resulting in the potential consequence of resistance evolution. A greenhouse dose-response experiment was conducted in the spring and summer of 2021 at the University of Arkansas System Division of Agriculture's Lonoke Extension Center located near Lonoke, Arkansas, to assess if ALS-inhibitor-resistant Pennsylvania smartweed was present within the state. Multiple rates (0.25x, 0.5x, 1x, 2x, 4x, and 8x of a label rate) of two ALS-inhibiting herbicides [bispyribac-sodium (Regiment) and halosulfuron + prosulfuron (Gambit)] were applied to smartweed populations screened. Results indicated the Jackson County, Arkansas, Pennsylvania smartweed population to be between 5- and 10-fold resistant compared to the susceptible Lonoke County, Arkansas population based on the ED50 (estimated dose to reduce biomass by 50%). To achieve 90% control of the Jackson County, Pennsylvania smartweed population, it required a 17x rate of Gambit and 48x rate of Regiment allowed by the label. These rates for control are not economically feasible nor legal due to the herbicide label. An alternate mode-of-action, development of a new chemistry, and/or implementation of diverse management strategies are needed to help combat this newly documented resistant weed. [ABSTRACT FROM AUTHOR]

In 2021, research was conducted to determine the optimum time to terminate a cover crop while also achieving suffi- cient weed control and optimum corn yield. The test was designed as a randomized complete block with 7 cover crop termination timings: 14 and 7 days prior to planting (DPP), at planting (AP), and 7, 14, 21, and 28 days after planting (DAP). A conventional tillage treatment was added for comparison and was treated with the standard herbicide program used for termination. All termination treatments consisted of glyphosate (Roundup PowerMax 2) applied at 40 oz/ac plus S-metolachlor (Dual II Magnum) at 1.3 pt./ac and atrazine (Aatrex) at 1 qt/ac. A standard postemergence (POST) application was made at the V4 corn stage across all treatments utilizing a premix of S-metolachlor, glyphosate, and mesotrione (Halex GT 2 qt/ac) plus atrazine (Aatrex 1 qt/ac). Pioneer 1197 YHR was planted on 5 April 2021, and a visual weed control assessment was taken 28 DAP. There was no difference in Palmer amaranth or barnyardgrass control when the cover crop was terminated 7 DPP, at planting, and 7, 14, 21, and 28 DAP. Palmer amaranth control ranged from 78% to 90%, while barnyardgrass control ranged from 81% to 91% controlled. The 14 DPP termination timing only provided 50% control of Palmer amaranth and 47% control of barnyardgrass, while the conventional tillage treatment provided the least (37%) control of both Palmer amaranth and barnyardgrass. Control of Palmer amaranth and barnyardgrass was increased to 94-99% for all termination timings following the V4 POST application, and no significant differences were observed from 7-21 days following the V4 application. Corn yields were highest (160-81 bu./ac) for 14 DPP, 7 DPP termination timings, and the conventional tillage treatments. Yields from plots where the cover crop was terminated at planting, 7,14, and 28 DAP ranged from 144 to 128 bu./ac. Cover crops terminated at 21 DAP resulted in the lowest yield of the study, only 125 bu./ac. [ABSTRACT FROM AUTHOR]

The use of preemergence herbicide technology has become increasingly critical in the fight against weeds due to postemergence herbicide resistance. The objective of this study was to evaluate the use of metobromuron for efficacy and crop tolerance in soybean [Glycine max (L.) Merr.], when used alone and in combination with Tricor® (metribuzin) in comparison to Tricor, Linex® (linuron) and Trivence® (chlorimuron-ethyl, metribuzin, and flumioxazin) applied alone. Visual estimations of weed control for Palmer amaranth (Amaranthus palmeri S. Wats.) and soybean crop injury were collected 14, 28, and 35 days after the herbicide application. Weed control ratings ranged from 67.5% for metobromuron (2.11 pt/ac), as the least effective treatment, to 100% for Trivence at 28 days after application. No visual injury was observed on soybean from any treatment. These data demonstrate the importance of including preemergence herbicides in a successful weed management program as well as combining chemicals that utilize multiple, effective modes of action. [ABSTRACT FROM AUTHOR]

The most problematic weed in mid-south soybean [Glycine max (L) Merr.] is Palmer amaranth (Amaranthus palmeri S. Wats.). While the shift to Xtend® soybean technology has provided another option of control for this weed, it has allowed for other troublesome weeds to be re-introduced to production soybean. One of those potentially yield-robbing weeds is prickly sida (Sida spinosa L.) also known as teaweed. A field study was conducted at the University of Arkansas System Division of Agriculture’s Jackson County Extension Center near Newport, Ark. in 2020 to evaluate the efficacy and crop safety of preemergence (PRE) herbicides in Xtend® soybean. The study was a randomized complete block design with four replications and consisted of 10 total treatments: a nontreated control, a weed-free control, and 8 PRE herbicide treatments. A blanket postemergence (POST) application of Intact® (drift control aid) + Class Act Ridion® (adjuvant) + Tavium® plus Vaporgrip (dicamba + S-metolachlor) + Roundup® PowerMax® (glyphosate) was broadcast across the entire trial area 41 days after planting. All treatments provided equal control of Palmer amaranth 40 days after the PRE application. Prickly sida was controlled greater than 98% by all PRE treatments following the blanket POST application except for PRE treatments consisting of Boundary® (S-metolachlor + metribuzin) and BroadAxe® (sulfentrazone + s-metolachlor). There was no visual soybean injury observed with any treatments. Several PRE residual herbicides were shown to be effective at controlling both Palmer amaranth and prickly sida within Xtend soybean. [ABSTRACT FROM AUTHOR]

Off-target movement of spray particles, vapor drift, and tank contamination has occurred with the use of synthetic auxin herbicides near crops that are not resistant. Field trials were conducted in 2020 to evaluate the effects of multiple rates of auxin herbicides [2,4-D (Enlist One®), dicamba (Xtendimax®), florpyrauxifen-benzyl (Loyant®), and quinclorac (Facet®)] on susceptible soybean [Glycine max (L.) Merr] during different growth stages. Visual estimations of injury, unmanned aerial system (UAS) UAS imagery reflectance data, and yield data were collected to determine damage. Injury observed from each synthetic auxin herbicide varied slightly in symptomology. Applications made at both vegetative and reproductive stages resulted in visual crop response. Reflectance data from UAS imagery closely matched visual estimations of injury and yield data supporting ground-based assessments. Xtendimax and Loyant were the most damaging synthetic auxin herbicides to soybean at reduced rates and could cause yield loss. Further research is needed to evaluate the implications of reduced rates of each of these synthetic auxin herbicides on soybean and the role UAS imagery may play in their identification and severity. [ABSTRACT FROM AUTHOR]

Sulfonylurea herbicides have been found effective in controlling glyphosate-resistant Italian ryegrass [Lolium perenne L. ssp. multiflorum (Lam.) Husnot] in fields planted to corn (Zea mays L.). FullPage™ rice (Oryza sativa L.) was released in 2020 on a limited basis and has been found to provide increased tolerance to imazethapyr and imazamox herbicide. Two experiments were conducted on a silt loam soil in Tillar, Arkansas, in 2020 and 2021 to determine the tolerance of FullPage™ rice to sulfonylurea herbicides applied preemergence (PRE) and postemergence (POST). Treatments consisted of Resolve Q (rimsulfuron + thifensulfuron) at 1.25 and 0.625 oz/ac, Steadfast Q (nicosulfuron + rimsulfuron) at 1.5 and 0.75 oz/ac, and Accent Q (nicosulfuron) at 0.75 and 0.375 oz/ac. When applied PRE, minimal levels of stunting were observed from most treatments within two weeks after application. When applied POST, crop stunting, chlorosis, leaf malformation, and necrosis were observed with most treatments, with crop stunting being more prevalent throughout the season. In 2020, within 14 days after the POST application (DAPOST), all treatments exhibited varying levels of stunting and chlorosis, with both rates of Steadfast Q resulting in the highest levels of injury. Similarly, by 35 DAPOST, the rates of Steadfast Q continued to exhibit observable levels of stunting. Regardless of the levels of phytotoxicity earlier in the growing season, rice yields were comparable across all treatments when compared to the weed-free check. In 2021, both rates of Resolve Q and Steadfast Q exhibited 8% to 23% stunting at 14 DAPOST. By 45 DAPOST, Steadfast Q at 1.5 oz/ac resulted in a significant delay in heading compared to the weed-free check, in addition to a significant yield reduction. These data suggest that when applied before rice planting or at planting, sulfonylurea herbicides may be beneficial in controlling herbicide-resistant Italian ryegrass. Although minimal yield reduction was observed when these herbicides were applied POST, significant levels of phytotoxicity were observed from all treatments. [ABSTRACT FROM AUTHOR]

Cotton (Gossypium hirsutum L.) herbicide systems that contain multiple modes of action and are applied timely are essential in controlling Palmer amaranth (Amaranthus palmeri). Arkansas cotton growers need new and improved methods and chemistry to manage this and other troublesome weeds. Trials were established in 2019 and 2020 to evaluate weed efficacy and crop response following Loyant applications post-directed in cotton. Trials were established at Marianna, Arkansas, in a Loring silt loam soil and at Tillar, Arkansas, in a Herbert silt loam soil. In 2019, PHY 350 W3FE was established at Tillar and DP 1646 B2XF at Marianna; while in 2020, PHY 400 W3FE was established at both locations. The trials were arranged in a randomized complete block design with four replications. All treatments received Brake FX preemergence at 40 oz/ac (fluometuron 33.2 oz/ac + fluridone 6.8 oz/ac) followed by Liberty (glufosinate) at 32 oz/ac plus Dual Magnum (metolachlor) at 21oz/ac at 3-4 leaf cotton. Post-directed herbicides evaluated included Loyant (florpyrauxifen-benzyl) at 5, 8, and 16 oz/ac, Durango (glyphosate) at 32 oz/ac and Roundup PowerMax (glyphosate) at 32 oz/ac. In 2019 and 2020, post-direct applications of Loyant were applied to 8- or 10-node cotton. Palmer amaranth control and epinasty were recorded at 21 days after 10-node post-direct applications at both locations. Loyant provided greater than 89% control of Palmer amaranth, as long as the rate applied was 8 oz/ac or greater. Cotton injury was significant when Loyant was applied at the 8-node growth stage; however, injury was generally reduced when applications were made to 10-node cotton. Yield reductions from all Loyant applications were observed at Marianna in 2019. No significant yield reductions were observed at either location in 2020, with the exception of, Loyant 16 oz/ac applied to 8-node cotton at Marianna. [ABSTRACT FROM AUTHOR]

In 2019 and 2020, 2 experiments were conducted to determine if Group 15 (chloroacetamide) herbicides could continue to control Palmer amaranth and if control differed by application rate. Chloroacetamide herbicides including Dual Magnum®, Outlook®, Warrant®, and Zidua® SC were applied preemergence (PRE) at various rates to determine the length of residual control of a Palmer amaranth (Amaranthus palmeri S. Wats) population with known resistance to metolachlor and a population with no known metolachlor resistance. In the 2019 experiment, only Outlook provided control greater than 90% of metolachlor-resistant Palmer amaranth at 2 weeks after application (WAA) at rates of 12.8 oz/ac and 16 oz/ac. All chloroacetamide treatments provided less than 75% control of this population 4 WAA. In the trial conducted in 2020, all chloroacetamide applications provided greater than 90% control of Palmer amaranth with no known metolachlor resistance, excluding either application rate of Warrant 2 WAA. Dual Magnum at 32 oz/ac, Outlook 16 oz/ac, and Zidua at any rate, provided greater than 70% 4 WAA. The highest rate of Zidua (5 oz/ac) provided the most control (85%) in the study by 4 WAA. Chloroacetamide herbicides are not as effective in controlling Palmer amaranth populations with known resistance to metolachlor. Results indicated that Outlook provided the best control to a resistant population at 2 WAA, but control was significantly reduced at the later evaluations. Control of the non-metolachlor-resistant biotype was consistent with all chloroacetamide herbicides, depending on rate, except Warrant. [ABSTRACT FROM AUTHOR]

In 2020, a weed control study was conducted at the University of Arkansas System Division of Agriculture’s Lonn Man Cotton Research Station near Marianna, Ark., on a Calloway silt loam soil to determine adequate weed control from a full season approach in Enlist® E3 soybeans [Glycine max (L.) Merr.]. The objective of this trial was to evaluate herbicide combinations for burndown control of large Canadian horseweed (Conyza canadensis) commonly called Marestail as well as other winter annuals. Enlist soybean were planted 15 days after burndown herbicide applications and additional herbicide programs were evaluated to determine efficacy on Marestail, Palmer amaranth, and other problematic weeds. Results indicated that herbicide programs containing Elevore® at 1 oz/ac provided the best control of Marestail, with the combination of Enlist One® 32 oz/ac and Durango® 32 oz/ac providing 90% control of Marestail and other winter annual weeds. Gramoxone® 40 oz/ac plus Verdict® 5 oz/ac provided only 73% control of Marestail but controlled Palmer amaranth 98% at the time of planting. Herbicide combinations at planting (PRE) consisted of either Trivence® 8 oz/ac plus 40 oz/ac Gramoxone or Boundary® 32 oz/ac plus 40 oz/ac Gramoxone. There was no difference in residual control of Palmer amaranth with any PRE 14 days after application (DAA). However, Marestail control was higher (>92%) where combinations of Gramoxone plus Trivence were applied compared to <75% with combinations of Gramoxone plus Boundary. This was likely due to the increased control with Elevore treatments before PRE applications. All other winter or summer annual weeds were controlled effectively following early postemergence (POST) applications, regardless of treatment. [ABSTRACT FROM AUTHOR]

Hemp sesbania (Sesbania herbacea) and northern jointvetch (Aeschynomene virginica) are among the top ten problematic rice (Oryza sativa) weeds in Arkansas. Several options are available for early-season control; but in the event of a failure or escape, there are few options for a post-flood salvage treatment that will provide adequate control. A field study was conducted in the summer of 2019 to evaluate halosulfuron (Permit), halosulfuron + thifensulfuron (Permit Plus), and halosulfuron + prosulfuron (Gambit) applied alone at multiple rates on hemp sesbania and northern jointvetch. Rates consisted of Permit at 0.33, 0.67, 1.00, and 1.33 oz/ac, Permit Plus at 0.38 and 0.75 oz/ac, and Gambit at 0.50, 1.00, 1.50, and 2.00 oz/ac. All treatments provided 100% control of both weed species at 3 weeks after treatment (WAT). At pre-harvest, all treatments still provided excellent control of greater than 94%. Permit and Gambit each applied at 1.00 oz/ac had the greatest numerical control (98%) of northern jointvetch at pre-harvest. The lowest labeled rates of the evaluated acetolactate synthase (ALS)-inhibiting herbicides would be advisable as they successfully controlled these weed species and would be more economical for the grower. For example, Permit at 0.33 oz/ac, Permit Plus at 0.38 oz/ac and Gambit at 0.50 oz/ac all controlled northern jointvetch and hemp sesbania over 95% at pre-harvest. Hemp sesbania and northern jointvetch were successfully controlled in a post-flood salvage situation using ALS-inhibiting herbicides alone. [ABSTRACT FROM AUTHOR]

Furrow-irrigated rice (Oryza sativa L.) has gained popularity over the last two years in Arkansas. The objective of this research was to determine the most effective herbicide program for season-long weed control in furrow-irrigated rice. Experiments were conducted at the University of Arkansas System Division of Agriculture's Lon Mann Cotton Research Station in Marianna, Arkansas during the 2019 growing season. Several herbicide programs were evaluated, all of which contained Command (clomazone) preemergence (PRE) alone and in combination with other herbicide modes of action, followed by two postemergence (POST) applications of various herbicide combinations. Results indicate that applications of Command plus Sharpen PRE may provide the best broad spectrum weed control when Palmer amaranth is present. Multiple residuals applied PRE increased grass control, however later applications of Clincher combinations provided the highest control of troublesome grasses such as goosegrass. Multiple applications of Loyant at 6 to 8 oz/ac or Stam plus Grandstand provided the best control of Palmer amaranth. [ABSTRACT FROM AUTHOR]

Conventional (non-GMO) corn production has significantly increased in portions of Arkansas. These conventional hybrids do not contain the Roundup Ready trait, and thus, they are at risk from off-target movement of Roundup (glyphosate) from surrounding crops. Arkansas corn growers can benefit from growing conventional corn hybrids if the impact from off-target movement of Roundup can be understood and minimalized. Trials were conducted in 2019 and 2020 to evaluate the crop response following low rates of Roundup PowerMax applied to a conventional corn hybrid. In 2019, one trial was established with Gateway 7157 conventional hybrid at Tillar, Arkansas in a Hebert silt loam soil. In 2020, trials were established with the same hybrid at Tillar, Arkansas, in a Hebert silt loam soil, Marianna, Arkansas in a Loring Silt loam soil, and Fayetteville, Arkansas in a Captina silt loam soil. Trials were arranged in a randomized complete block design with four replications. Due to uniformity of data across location and years, data were pooled, and means were separated using Tukey-Kramer grouping for treatment least squares means at a = 0.05. All treatments received Aatrex at 64 oz/ac plus Dual II Magnum at 16 oz/ac applied preemergence followed by a Roundup PowerMax treatment at either stage V2 or V6 corn (Barber et al., 2020). Roundup PowerMax rates ranged from 0.32 oz/ac (1/100X) to 6.4 (1/5X) at each stage. Visual corn injury 14 days after V2 applications was highest, with Roundup at 6.4 oz/ac causing 91% and lowest with Roundup at 0.32 oz/ac causing 4%. Stage V2 corn injury increased as the herbicide rate increased, which was expected. Visual corn injury from V2 applications continued 14 days after V6 applications in a similar trend with Roundup applied at 6.4 and 3.2 oz/ac to V2 corn causing the highest injury at 72% and 53%, respectively. These two rates also caused the highest injury when sprayed at V6. Overall injury was higher when Roundup was applied at V2 vs. V6 growth stage. Roundup applied at 6.4 and 3.2 oz/ac rates to V2 corn caused the highest yield reduction, with corn yielding 21 and 68 bu./ac, respectively. Corn yields were not reduced from Roundup rates 1.6 oz/ac or lower for any growth stage. [ABSTRACT FROM AUTHOR]

Loyant™ with Rinskor™ active is a new synthetic auxin herbicide that provides broad spectrum control of most broadleaf, sedge, and aquatic weed species with additional activity on barnyardgrass. A study was conducted in 2018 at the University of Arkansas Pine Bluff-Lonoke farm to determine effectiveness of Loyant on barnyardgrass following single or multiple residual applications. Treatments in this experiment consisted of Command or Obey applied pre-emergence (PRE); Command, Obey, or Ricebeaux® applied early post-emergence (EPOST); and Loyant applied pre-flood. The PRE applications of Command and Obey provided similar control (>80%) of barnyardgrass 14 days after treatment (DAT). Treatments containing EPOST applications were necessary to maintain control 15 DAT with Command followed by (fb) Ricebeaux providing greater than 90% of both barnyardgrass and broadleaf signalgrass. The addition of Loyant pre-flood provided an increase in control as long as an EPOST application was made in addition to either Command or Obey applied PRE. All programs provided greater than 95% control, except for the two pass system of Obey fb Loyant. The two-pass program of Obey fb Loyant yielded less (125 bu./ac) than the three-pass-system of Obey fb Command fb Loyant program which provided the highest yield (157 bu./ac). [ABSTRACT FROM AUTHOR]

Generally, Arkansas rice producers utilize multiple herbicides throughout the growing season to combat problematic weeds. An experiment was conducted on a silt loam soil in Tillar, Arkansas to evaluate the effectiveness of applying multiple rates of Loyant alone or in combination with commonly applied graminicides. At 20 days after treatment (DAT), Loyant 16 oz/ac + Clincher 31 oz/ac provided the most effective control of hemp sesbania, barnyardgrass, and rice flatsedge, with 99%, 98%, and 99% control, respectively. A positive trend was observed throughout the growing season as the rate of Loyant increased when applied alone or in tank-mixture with the graminicides. By 42 DAT, reduction in barnyardgrass control was observed from all treatments. It can be determined by these data that the most effective combination to control the present weeds is Loyant at 16 oz/ac + Clincher at 31 oz/ac. Regardless of the graminicide, these data suggest that applying Loyant at 16 oz/ac aided in controlling the weeds commonly found in Arkansas rice. [ABSTRACT FROM AUTHOR]

Benzobicyclon is a new herbicide with activity on a broad array of weed species that is soon to be available to rice (Oryza sativa) growers. It is an 4-hydroxyphenolpyruvate dioxygenase (HPPD)-inhibiting herbicide and when registered would be the first Group 27 herbicide labeled in Arkansas rice. Hemp sesbania (Sesbania herbacea) and northern jointvetch (Aeschynomene virginica) are very troublesome weeds in rice due to their black seed characteristics, and more options for post-flood control are needed. The objective of this research was to determine the effectiveness of benzobicyclon alone and in combination with acetolactate synthase (ALS)-inhibiting herbicides post-flood on controlling hemp sesbania and northern jointvetch. A field study was conducted in the summer of 2019 at the University of Arkansas at Pine Bluff Small Farm Outreach Center near Lonoke, Arkansas to evaluate tank-mixture options of ALS-inhibiting herbicides [halosulfuron (Permit) and halosulfuron + prosulfuron (Gambit)] at multiple rates with benzobicyclon for the control of hemp sesbania and northern jointvetch. Treatments consisted of benzobicyclon at 8.40 oz/ac applied alone and in combination with Permit at 1.00 and 1.33 oz/ac and Gambit at 0.50, 0.75, and 1.00 oz/ac. All treatments provided 85% or greater control of hemp sesbania and northern jointvetch at 4 weeks after treatment with the exception of benzobicyclon alone which provided less than 10% control of both weed species. At pre-harvest, hemp sesbania control remained above 85% for all treatments excluding the benzobicyclon alone treatment which was less than 30%. Benzobicyclon plus Permit at 1.00 and 1.33 oz/ac and benzobicyclon plus Gambit at 1.00 oz/ac provided greater than 80% control of northern jointvetch while the remainder of the treatments provided less than 70% control. Benzobicyclon alone showed no control of northern jointvetch at pre-harvest. Hemp sesbania and northern jointvetch were controlled post-flood using ALS-inhibiting herbicides. Although benzobicyclon provided minimal to no control of these weed species, mixtures with ALS-inhibiting herbicides still provided satisfactory control when using full, labeled rates. [ABSTRACT FROM AUTHOR]