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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]

Chloroacetamide herbicides are unavailable for U.S. rice production, likely due to the high risk of injury and variability associated with an early application and activation timings. Environmental conditions can induce severe injury and stand loss at early application timings. Previous research from the University of Arkansas System Division of Agriculture has demonstrated the efficacy of Warrant® [acetochlor, Weed Science Society of America (WSSA) Group 15] to control problematic weeds in rice and a fenclorim seed treatment to reduce rice injury under typical drill-seeded rice-growing conditions but not under cool, saturated conditions. Therefore, two growth chamber experiments were initiated to evaluate rice tolerance with a 12-hour photoperiod, a night temperature of 55 °F, and a 75 °F day temperature. The experiment was designed as a three-factor factorial: with or without fenclorim (2.5 lb/1000 lb of seed), with or without Warrant (2.5 pt/ac) applied delayed-preemergence (DPRE), and a 0.25-in. or 1-in. planting depth. Rice shoots, heights, and visual injury estimates were recorded weekly until termination and biomass collection 30 days after emergence (DAE). The fenclorim seed treatment alone at 7 and 14 DAE caused a reduction in height by delaying emergence relative to the nontreated control, but height recovered by 21 DAE. Warrant alone caused injury ranging from 15% to 60%, while the fenclorim seed treatment reduced injury to rice from Warrant ranging from 0% to 20%. The deeper planting depth also improved tolerance to Warrant alone for all evaluations but did not provide commercial tolerance. Relative to the nontreated control, fenclorim alone improved aboveground rice biomass, while fenclorim and Warrant were comparable to the nontreated control and greater than Warrant alone. After 14 DAE, the fenclorim seed treatment enhanced crop tolerance to Warrant for all evaluations. Based on the results of this study, Warrant applied DPRE at 2.5 pt/ac with a fenclorim seed treatment should provide commercial tolerance in drill-seeded rice. [ABSTRACT FROM AUTHOR]

Sheath blight caused by Rhizoctonia solani AG1-1A is the most prevalent disease in rice fields of Arkansas causing up to 15% grain yield loss. Nearly 57% of rice fields in Arkansas receive at least one fungicide application every year and most of these fungicides are to manage sheath blight. In some commercial rice fields, low application spray volumes used to deliver fungicides to the crop are blamed for the lower efficacy of fungicides used to suppress diseases such as sheath blight and false smut. Field tests for sheath blight suppression were conducted for the 3rd season in 2021 to evaluate two volumes of water (3 and 10 gallons per acre) as a carrier to apply two fungicides (Amistar Top and Quilt Xcel at 15 and 21 fl oz/ac rates, respectively). The sheath blight data analysis showed significant difference in disease suppression and grain yield between the sprayed and unsprayed treatments. However, there was no significant difference in efficacy between Amistar Top and Quilt Xcel in the degree of sheath blight suppression. Sheath blight in unsprayed plots showed most progression throughout the season followed by the plots sprayed with 3 gal/ac. The highest suppression of disease was in plots that received fungicides sprayed using 10 gal/ac of carrier water. In false smut plots, there was no significant differences between the sprayed and unsprayed treatments in the number of galls counted on panicles collected from 8 ft2 or galls counted from 8.8 lb of harvested seed. Effects of both fungicides and the water volumes used to deliver were not significant in suppressing false smut. Although not significant, the unsprayed plots occasionally had lower diseased panicles or gall counts compared to the sprayed check. When visually compared, panicles of secondary tillers in plots that received fungicides appeared greener and carry more false smut galls than the unsprayed plots. The study on false smut is inconclusive and needs repeated study. [ABSTRACT FROM AUTHOR]

Due to genetic similarities between johnsongrass (Sorghum halepense L. Pers.) and grain sorghum (Sorghum bicolor L. Moench), few herbicides are available to effectively remove the troublesome weed without injuring the crop. In order to combat this issue, multiple new grain sorghum lines are being developed in grain sorghum to help producers by allowing over-the-top applications of herbicides previously unavailable, with some commercialized in 2021. These technologies include resistance to both acetyl CoA carboxylase (ACCase) and acetolactate synthase (ALS) inhibitors. Johnsongrass seed from locations in Arkansas were collected, and a greenhouse study was conducted in Fayetteville, Ark., in 2020 and 2021 to determine the effectiveness of the herbicides that will be labeled in these new technologies. Johnsongrass seeds were collected from 63 fields within six counties in eastern Arkansas. These accessions were threshed and then seeded in the greenhouse, where seedlings were treated with fluazifop at 0.09 lb/ac, quizalofop at 0.04 lb/ac, nicosulfuron at 0.03 lb/ac, and imazamox at 0.05 lb/ac. All herbicides were applied with 1% v/v crop oil concentrate. Overall, the two ACCase inhibitors, quizalofop and fluazifop, provided the highest levels of control, with a percent mortality of greater than 90% across all accessions tested aside from one accession from Crittenden County. These herbicides showed minimal variability in visual johnsongrass control and percent mortality. The lowest percent mortality was for nicosulfuron, which only controlled 87% of the plants treated. Imazamox resulted in 91% mortality of johnsongrass. Imazamox and nicosulfuron showed high levels of variability across all accessions. These findings show that imazamox and nicosulfuron will be ineffective at controlling Arkansas johnsongrass accessions in many fields. If Arkansas grain sorghum producers are planting into areas with known johnsongrass pressure, the best option is to utilize a technology that enables the use of quizalofop. [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]

Soybean [Glycine max (L.) Merr.] cropping systems are an essential part of agriculture in the United States. Palmer amaranth [Amaranthus palmeri (S.) Watson] is one of the most troublesome weeds in these systems and can reduce yields for producers. Herbicide resistance has posed new obstacles to controlling Palmer amaranth. Methods such as mechanical seed destruction can add another option for producers to combat this troublesome weed. Field trials were initiated at both the University of Arkansas System Division of Agriculture's Jackson County Extension Center located near Newport, Arkansas, and the Northeast Research and Extension Center located in Keiser, Arkansas, to assess how desiccation of soybean infested with Palmer amaranth affects shattering of the weed and the effectiveness of a Redekop™ seed destructor. Treatments of 5 different desiccants were applied to plots, and plots were then split with harvest weed seed control and no harvest weed seed control being the subplot factor. Results showed that harvest weed seed control significantly reduced the number of viable seeds returning to the soil seed bank by 60% at the Keiser location and 64% at the Newport location. Treatment and the interaction between treatment and harvest weed seed control were insignificant. With Palmer amaranth resistance making it harder to control, using methods such as a Redekop seed destructor as a harvest weed seed control tactic can help combat the growing problem. [ABSTRACT FROM AUTHOR]

Johnsongrass [Sorghum halepense (L.) Pers.] escapes and infestations have been a growing issue for soybean [Glycine max (L.) Merr.] producers across the mid-south. Reliance on glyphosate and acetyl CoA carboxylase (ACCase) inhibitors for grass control could have increased resistant populations. A greenhouse study was conducted in Fayetteville, Ark., in 2020 and 2021 to determine the extent of johnsongrass in Arkansas with resistance to aryloxyphenoxypropionate herbicides and glyphosate. Johnsongrass seeds were collected from 63 locations within 6 counties in eastern Arkansas. These accessions were seeded in the greenhouse and treated with fluazifop at 0.9 lb ai/ac, quizalofop at 0.04 lb ai/ac, and glyphosate at 0.77 lb ae/ac. The only treatment resulting in 100% mortality of all accessions was quizalofop. Some escapes were observed to fluazifop, but all accessions, outside of one from Crittenden County, had greater than 90% control. Variable levels of mortality, ranging from 10% to 100%, were observed with glyphosate. Overall, Arkansas johnsongrass accessions showed high levels of variability in control when treated with glyphosate, while fluazifop and quizalofop applications appeared effective on the accessions tested. [ABSTRACT FROM AUTHOR]

Water is the most extensively used carrier for pesticide applications, and spray water quality (pH, hardness, and cation concentrations) has been shown to severely impact herbicide efficacy. The objective of this survey was to assess spray water used for herbicide applications from across Arkansas for pH, hardness, and cation concentration. Samples were solicited through multiple avenues in 2019 and 2020 and tested for pH, calcium (Ca2+), magnesium (Mg2+), sodium (Na+), and iron (Fe3+) concentrations, and a hardness index (based on Ca2+ and Mg2+ concentrations). A total of 79 spray water samples were collected and analyzed from across the state. Results indicated approximately 71% of the samples had a pH greater than 7 (alkaline), and 39% of the samples had a hardness index greater than 200 ppm (Very Hard). These levels have the potential to cause a loss in weed control. Cation testing also indicated that Na+ and Fe3+ were present in large enough concentrations in some samples from multiple counties to antagonize herbicides, causing an additional reduction in weed control. As a result, it is important to have a holistic spray water analysis across multiple cations as the Ca2+ and Mg2+ hardness index does not account for and correlate with the presence of other problematic cations that could tie up herbicide active ingredients. Future research will investigate the water quality effect on weed control from herbicides, and what adjuvants, if any, help to mitigate these effects. [ABSTRACT FROM AUTHOR]

Dicamba and glufosinate have been effective herbicides used for postemergence weed control in XtendFlex® technology. The occurrence of Palmer amaranth (Amaranthus palmeri S. Wats.) escapes in fields that rely on these tools demonstrate the importance of monitoring the emergence and spread of herbicide resistance. For that purpose, Palmer amaranth accessions were collected from fields in regions where auxins (dicamba or 2,4-D) and glufosinate are heavily relied upon for weed control. Collections occurred in the fall of 2018, 2019, and 2020 from fields located in Mississippi, Missouri, Nebraska, Illinois, Louisiana, Tennessee, and Arkansas. Every state did not sample for Palmer amaranth each year. Herbicide treatments equivalent to a 0.5X or 1X rate of dicamba at 0.25 and 0.5 lb ae/ac or glufosinate at 0.26 and 0.53 lb ai/ac were applied to greenhouse-grown plants at the 5- to 6-leaf stage. Some accessions could not be thoroughly evaluated due to limited seed availability or lack of seed viability. For all samples reported, at least 100 plants were assessed. Thus far, the screening has evaluated 193 and 206 accessions to dicamba and 210 and 215 accessions to glufosinate at a 0.5 and 1X rate of each herbicide, respectively. Evaluations of the accessions showed a high variability of plant responses to the herbicide treatments. Dicamba and glufosinate applied at a 0.5X rate resulted in less than 60% mortality to 22 and 31 accessions, respectively. Nevertheless, a full labeled (1X) rate of dicamba and glufosinate provide at least 80% mortality of 193 and 194 Palmer amaranth accessions, respectively. Future experiments will be conducted to determine the mechanism for reduced susceptibility to these herbicides as well as alternative herbicides that can be used to control these troublesome accessions. [ABSTRACT FROM AUTHOR]

Dicamba formulations like Engenia®, Fexapan®, and Xtendimax® plus VaporGrip® are labeled for over-the-top use in the XtendFlex™ soybean [Glycine max (L.) Merr.] technology system; however, mixtures of dicamba and glufosinate cannot be utilized. In 2019, a field study was conducted in Crawfordsville, at the University of Arkansas System Division of Agriculture’s Northeast Research and Extension Center near Keiser, and the Lon Mann Cotton Research Station near Marianna, Ark. In 2020, the same field study was conducted at the University of Arkansas System Division of Agriculture’s Milo J. Shult Agricultural Research and Extension Center in Fayetteville, and repeated near Keiser, and Marianna, Ark. to evaluate the efficacy of sequential applications of dicamba and glufosinate when applied at 0.2- (6 hours), 3-, 7-, 14-, and 21-day intervals from the initial application on native Palmer amaranth (Amaranthus palmeri) populations. Field experiments were conducted to determine if the time interval between sequential applications and/or sequence of herbicides could be optimized to improve Palmer amaranth control. Palmer amaranth control was optimized in the dicamba only and glufosinate only systems when sequential applications were made at the 14-, and 21- day-interval, and 7 day-interval, respectively. Palmer amaranth control was improved on larger-than-labeled weed sizes when dicamba was followed by glufosinate at the 14 day-interval. Only when dicamba was followed by glufosinate at the 14 day-interval on labeled weed sizes was 100% Palmer amaranth control achieved. These findings highlight the importance of utilizing both dicamba and glufosinate inseason and making the first application to labeled weed sizes. [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]

Metribuzin is a photosystem II (PSII) inhibitor, primarily used as a preemergence (PRE) herbicide for residual weed control in soybean [Glycine max (L.) Merr.]. This herbicide, widely used in the mid-South for control of Palmer amaranth [Amaranthus palmeri (S.) Wats] in soybean, can cause severe injury and yield loss if a highly sensitive variety is planted and sprayed. Because of the importance of metribuzin in soybean for control of Palmer amaranth in Arkansas, a greenhouse screening was conducted in 2020 evaluating current soybean varieties and their tolerance to a labeled rate of soil-applied metribuzin. Injury, which was evaluated at 14 and 21 days after treatment (DAT), showed that nearly 59% of the tested varieties showed little to no response. Thirty-six percent of the tested varieties showed symptoms and were labeled as moderately tolerant to the herbicide. The remaining 5% of varieties screened exhibited severe injury when treated with metribuzin and should be avoided if metribuzin is included in a weed control program. Regardless of the herbicide technology chosen by a grower, there are sufficient varieties that allow metribuzin to be integrated into weed control programs that focus on controlling Palmer amaranth. [ABSTRACT FROM AUTHOR]

The commercialization of dicamba-resistant soybean [Glycine max (L.) Merr.] has brought forth concerns of offtarget movement of dicamba onto non-target vegetation. In order to mitigate off-target movement, producers and applicators are considering applications that do not broadcast herbicide via spray droplets, such as rope wicks and other wiper-type applicators. While wiper-type applications have been made in-crop before, the use of auxin-type herbicides such as dicamba has not been investigated. Two studies were conducted at the University of Arkansas System Division of Agriculture’s Northeast Research and Extension Center near Keiser and the Milo J. Shult Agricultural Research and Extension Center in Fayetteville in the summer of 2020 to determine the optimum application parameters for roller wiper application of dicamba in soybean. This study was designed as a 3-factor factorial with the first factor being target weed height, the second being herbicide concentration, and the third being the number of application directions. Results from these studies found that Palmer amaranth [Amaranthus palmeri (S.) Wats.] mortality increased from 31% for a single application direction to 43% with the addition of a second application direction. Mortality also increased from 30% to 44% as a result of increased herbicide concentration. An increase in soybean injury was observed with the higher herbicide concentration, but there was no impact on grain yield. The findings from this study could aid producers in optimizing wiper applications of dicamba if these practices become common. [ABSTRACT FROM AUTHOR]

Following the commercial launch of Loyant® (florpyrauxifen-benzyl) in 2018, frequent off-target movement of the herbicide to adjacent soybean [Glycine max (L.) Merr.] fields was observed. Hence, field experiments were conducted in 2020, at the University of Arkansas System Division of Agriculture’s Milo J. Shult Agricultural Research and Extension Center in Fayetteville, Ark, to evaluate soybean injury following low rates (0.003 oz ai/ac to 0.094 oz ai/ac) of florpyrauxifen-benzyl applied either as a foliar spray or coated on urea at the V3 stage. In 2 separate field experiments, the response of soybean was evaluated when florpyrauxifen-benzyl was applied in wide-row (36-in.wide rows) and narrow-row (7-in.wide rows) systems at 7, 14, 21, and 28 days after application. In both experiments, 100% soybean injury (death) occurred following foliar spray applications in both wide- and narrowrow soybean. However, when coated on urea, the maximum soybean injury from florpyrauxifen-benzyl occurred at 0.094 oz ai/ac was 20% and 24% in wide- and narrow-row soybean, respectively. At all timings, an equivalent rate of florpyrauxifen-benzyl on urea caused less injury than that of the foliar applications. Overall, florpyrauxifenbenzyl coated on urea reduced soybean injury 50% to 91% and 61% to 92% in wide- and narrow-row soybean, respectively, across all rating dates when compared to foliar applications. Impregnating florpyrauxifen-benzyl onto urea appears to substantially reduce the risk for off-target movement of the herbicide onto soybean and may allow for a means of safely applying the herbicide by air. Additional research is underway to establish the effectiveness of this application technique on weed control. [ABSTRACT FROM AUTHOR]

Warrant® is a microencapsulated (ME) formulation of the Weed Science Society of America's Group 15 herbicides, acetochlor, capable of controlling both grasses and small-seeded broadleaf weeds. Acetochlor is traditionally used in row crops such as corn, cotton, and soybean as a residual herbicide and is not currently labeled for use in rice. A fenclorim seed treatment combined with a delayed preemergence application timing can potentially reduce injury. In 2021, an experiment was conducted in Keiser, Arkansas to evaluate the effectiveness of acetochlor as Warrant for both weed control and injury to rice on a clay soil. The experiment involved three rates of acetochlor (1.12, 1.68, and 2.25 lb ai/ac), with and without a fenclorim seed treatment at (2.5 lb ai/1000 lb-seed). All applications occurred at a delayed preemergence application timing at 15 gallons per acre (GPA). Control of three problematic weeds (Palmer amaranth, horse purslane, and broadleaf signalgrass) and rice injury were rated at 28 days after treatment (DAT). Palmer amaranth control was numerically greatest when acetochlor was applied at 2.25 lb ai/ac (93%) but did not significantly differ from 1.68 lb ai/ac (83%). In terms of horse purslane and broadleaf signalgrass, weed control was the highest at a rate of 2.25 lb ai/ac at 75% and 88% respectively and was greater than both other rates of acetochlor. Injury to 'Diamond' rice was reduced with the use of a fenclorim seed treatment at acetochlor rates of 1.68 and 2.25 lb ai/ac when compared to those rates without a fenclorim seed treatment. Fenclorim as a seed treatment provides the opportunity for ME acetochlor to be safely used in a drill-seeded rice production system on a clay soil. [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]

Fluridone is a pigment-inhibiting herbicide with applications in cotton [Gossypium hirsutum (L.)] (Brake®) and aquatic systems (SonarOne®). The success of Brake in Arkansas cotton systems has led the University of Arkansas System Division of Agriculture to evaluate this herbicide as an alternative for residual broadleaf control in flooded and furrow-irrigated rice systems. An experiment was conducted near Stuttgart, Arkansas, in 2021 to evaluate the tolerance of a drill-seeded inbred rice cultivar to early-season applications of Brake. Treatments were arranged as a two-factor factorial randomized complete block design with four replications. The first factor was herbicide rate, and the second was application timing. Brake was applied at 16 and 32 fl oz/ac at the preemergence (PRE), delayed-preemergence (DPRE), 1-2 leaf, and postflood (POSTFLD) timings. An interaction was observed between herbicide rate and application timing at 28 days after treatment (DAT), as well as at 28 days after postflood (DA POSTFLD). Except for comparable injury at the POSTFLD timing, visual injury from Brake applied at 16 fl oz/ac was less than the 32 fl oz/ac rate for each assessment. The greatest amount of injury at 28 DAT and 28 DA POSTFLD resulted from a postemergence application at the 1-2 leaf rice growth stage at the 32 fl oz/ac rate (33% and 31%, respectively). Brake applied at 16 fl oz/ac at the PRE and DPRE timing caused less than 10% injury to rice for each assessment, which is an acceptable level of crop injury. Overall, rice was tolerant to Brake applied at 16 fl oz/ac, and crop injury did not appear to increase with the establishment of a continuous flood. [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]

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]

Palmer amaranth (Amaranthus palmeri S. Watson) is a very difficult to control weed in different cropping systems including cotton (Gossypium hirsutum L.) and soybean [Glycine max (L.) Merr.]. Different chemistries have been used to control it, gradually leading to a loss of susceptibility. A Palmer amaranth accession was collected in eastern Arkansas after the failure of glufosinate to effectively control this weed in cotton. Under greenhouse conditions, the application of glufosinate at the recommended field rate (1×, 32 fl oz/ac) has not been effective. The objective of this research was to elucidate if single nucleotide polymorphisms are involved in the recently documented resistance within this accession. For that purpose, the glutamine synthetase (GS) gene was sequenced following standard procedures. Comparison of the nucleotides and their deduced protein between resistant and susceptible accessions have revealed no amino acid substitution at position 171, the site where resistance has occurred in other weeds. The outcome of this research suggests that the resistant accession most likely has a resistance mechanism other than a target-site mutation that leads to the ineffectiveness of glufosinate on this population. [ABSTRACT FROM AUTHOR]

The N,N-bis(3-aminopropyl)methylamine (BAPMA) salt of dicamba (Engenia®) and diglycolamine (DGA) salt of dicamba with VaporGrip™ (XtendiMax™) are labeled for preemergence and postemergence control of broadleaf weeds in Xtend™ cotton (Gossypium hirsutum L.) and soybean [Glycine max (L.) Merr] systems. Dicamba applications to cotton and soybean have resulted in a record number of complaints regarding the off-target movement of the herbicide since the initial introduction in 2017. To counteract dicamba volatility, the University of Arkansas System Division of Agriculture has pursued potassium tetraborate tetrahydrate (potassium borate) as a volatilityreducing tank additive following the success of preliminary volatility experiments conducted in 2019. To investigate the impact of this additive on weed control in an Xtend-based system, an experiment was conducted in 2020 to evaluate the efficacy of dicamba when mixed with the additive on Palmer amaranth (Amaranthus palmeri S. Watson) and johnsongrass (Sorghum halepense L. Pers). Two low-volatile dicamba formulations (XtendiMax and Engenia) plus the potassium salt of glyphosate (Roundup PowerMax®) were combined with potassium borate at 0, 0.015, 0.3, and 0.1 M concentrations. No concentration of potassium borate compromised broadleaf or grass weed control when added to either formulation of dicamba, although some numerical decreases were observed. Overall, the addition of potassium borate to dicamba has great potential in reducing the off-target movement of dicamba without sacrificing efficacy on key weed species. [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]

Palmer amaranth [Amaranthus palmeri (S.) Wats] is one of the most problematic weed species across multiple cropping systems in Arkansas. Palmer amaranth is resistant to nine modes of action, making the weed difficult for producers to control. Diflufenican (DFF) is a Weed Seed Science Society of America (WSSA) group 12 herbicide that will likely be labeled for use in soybean. Although DFF is targeted for use in soybean, additional research is being conducted to evaluate the potential for the herbicide to carryover and injure common rotational crops. Therefore, an experiment was conducted at the Rice Research and Extension Center near Stuttgart, AR, to evaluate the sensitivity of rice (Oryza sativa L.) to low concentrations of DFF in the soil. Applications of DFF were applied preemergence (PRE) at 0.0065, 0.0125, 0.25, 0.5, and 1.0 times the anticipated 1X rate. By 2 weeks after emergence (WAE), the highest injury observed was 20% when a 1X rate was applied, and injury decreased as the rate of DFF decreased. Rice shoot counts were taken 2 WAE and no differnences were observed between treatments. By 5 WAE, less than 5% injury was observed in all treatments evaluated. Grain yield was collected at maturity, and no differences were observed among treatments. Overall, there does not appear to be a high risk for herbicide carryover to rice from soybean that received an application of DFF during the previous growing season. [ABSTRACT FROM AUTHOR]

The ROXY® Rice Production System (RRPS) was recently commercialized in California, allowing producers to apply oxyfluorfen (HRAC/WSSA Group 14) both preemergence and postemergence. The use of oxyfluorfen in the RRPS provides producers with an additional herbicide option for barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] control in rice (Oryza sativa L.). A field experiment was conducted at the University of Arkansas System Division of Agriculture's Rice Research and Extension Center near Stuttgart, Ark., in 2022, to evaluate residual barnyardgrass control with clomazone and oxyfluorfen alone and in mixture. Herbicide treatments included clomazone at 0.25 or 0.3 lb ai/ac, and oxyfluorfen at 0.6 or 0.75 lb ai/ac applied preemergence followed by a sequential postemergence application. A 1:2 and 1:3 ratio of clomazone and oxyfluorfen (0.3 + 0.6 lb ai/ac and 0.25 + 0.75 lb ai/ac) were also evaluated. At 3 weeks after the preemergence application, but prior to the postemergence application, all rates of oxyfluorfen and clomazone alone provided =94% visual control of barnyardgrass. All combinations of clomazone and oxyfluorfen, provided 100% barnyardgrass visual control at 3 weeks after the preemergence application. At 5 weeks after the postemergence application, all treatments provided = 94% barnyardgrass control. At 6 weeks after the postemergence application, mixtures of clomazone and oxyfluorfen provided 95% or greater barnyardgrass control. Conversely, when sequential applications of oxyfluorfen alone were made, regardless of rate, barnyardgrass control was only 77% and 79% at 6 weeks after the postemergence application. When clomazone and oxyfluorfen were applied at a 1:3 ratio and 1:2 ratio or clomazone alone applied at 0.3 lb ai/ac, rice yields were comparable among treatments, ranging from 106 to 130 bu./ac. Treatments of oxyfluorfen at 0.6 and 0.75 lb ai/ac, and clomazone at 0.25 lb ai/ac, resulted in rice yields of 74 to 93 bu./ac. These results indicate that clomazone will likely be needed with oxyfluorfen to obtain extended residual barnyardgrass control in the RRPS. [ABSTRACT FROM AUTHOR]

A new soybean technology (LibertyLink® GT27™) has been approved for commercial production in the United States to provide growers with an alternative, effective weed control program utilizing multiple modes-of-action. The objective of this research was to evaluate herbicide weed control programs containing glufosinate (Liberty®), glyphosate (Roundup PowerMax®), and isoxaflutole [a 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibiting herbicide awaiting EPA approval] for their effect on efficacy and crop tolerance in LibertyLink® GT27™ soybean. A field experiment was conducted at the University of Arkansas System Division of Agriculture's Newport Extension Center, near Newport, Arkansas in the summer of 2018. Weed control programs containing residual herbicides at both pre-emergence (PRE) and post-emergence (POST) timings provided excellent, season-long control of Palmer amaranth [Amaranthus palmeri (S.) Wats.] and yellow nutsedge [Cyperus esculentus (L.)]. Minimal visible crop injury was observed across weed control programs evaluated in this research; therefore, isoxaflutole will be an excellent addition to LibertyLink® GT27™ soybean weed control programs. A numerical decrease in Palmer amaranth control was observed from a Liberty® and Roundup PowerMax® tank-mixture compared to other herbicide programs indicating a potential antagonistic interaction occurred. Herbicide program recommendations for LibertyLink® GT27™ soybean should include a pre-emergence followed by a post-emergence application with residuals to provide season-long weed control and increase post-emergence application flexibility. [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]

Benzobicyclon is a new herbicide option for Arkansas rice (Oryza sativa) that is being evaluated for post-flood weed control. Benzobicyclon is a 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor and when registered would be the first group 27 herbicide labeled in Arkansas rice. This brings a new tool to rice growers who battle problematic grass and broadleaf weeds. A field experiment was conducted at the University of Arkansas at Pine Bluff small farm outreach center in Lonoke, Arkansas in the summer of 2018 to evaluate Amazon sprangletop (Diplachne panicoides) control with the use of benzobicyclon herbicide in flooded rice. Early results show that benzobicyclon is an excellent option for the control of Amazon sprangletop. [ABSTRACT FROM AUTHOR]

Four hybrid rice varieties have been made commercially-available (FullPage™) to provide greater imidazolinone herbicide tolerance and reduce potential rice injury. The objective of this research was to evaluate rice herbicide programs, including imidazolinone chemistries, on crop tolerance and weed control within a FullPage™ rice cropping system. Field experiments were conducted at the University of Arkansas at Pine Bluff farm near Lonoke, Arkansas and the University of Arkansas System Division of Agriculture's Rice Research and Extension Center near Stuttgart, Arkansas in the summer of 2018. Results indicated FullPage™ rice had greater tolerance to the imidazolinone herbicides (imazethapyr and imazamox) than its Clearfield® rice counterparts, especially early season. Additionally, multiple herbicide programs provided sufficient season-long control of barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] and hemp sesbania [Sesbania herbacea (Mill.) McVaugh] in a FullPage™ rice cropping system while maintaining rough rice yield. [ABSTRACT FROM AUTHOR]

Engenia and XtendiMax with VaporGrip are labeled dicamba products for preemergence and postemergence control of broadleaf weeds in XtendFlex cotton and Roundup Ready 2 Xtend soybean. Despite the efficacy of dicamba on problematic weeds in the mid-South, labeled applications of Engenia and XtendiMax in both cotton and soybean have presented major concerns for off-target movement, primarily to non-dicamba-resistant soybean. Extensive research has been published regarding the effects of sublethal concentrations of dicamba at multiple growth stages in soybean; however, there is limited research investigating the impact of dicamba on reproductive rice. To determine the potential consequences of dicamba drift rates on reproductive rice, an experiment was conducted near Stuttgart, Arkansas in 2018 and 2019. Dicamba at rates of 1, 1/10, 1/100, and 1,1000X, with 1X being 227 g ae/ac, were applied to rice at three reproductive growth stages (late boot, panicle exertion, and anthesis). Treatments were arranged as a two-factor factorial, with the first factor being dicamba rate, and the second being rice growth stage. There were no significant treatment effects observed for 100-seed weight, although dicamba rate played a significant role on the relative average panicle weight with a 15% and 39% reduction at the 1/10 and 1X rate, respectively. The same trend translated to reductions in both average number of seeds per panicle and grain yield, with a decrease of approximately 14% and 35%. An interaction was observed between dicamba rate and growth stage as well, with 1/10 and 1X rates of dicamba hastening rice maturity roughly 2 and 3 days, respectively. With severe consequences only being observed at high dicamba rates, the threat that off-target movement poses to rice is far less severe than what has been observed in soybean. [ABSTRACT FROM AUTHOR]

Dicamba is a herbicide currently used in Arkansas for broadleaf weed control in Xtend® and XtendFlex® cotton, soybean, corn, grain sorghum, and non-crop systems but is not labeled for use in rice. If a safe application time and rate can be determined for rice, dicamba could serve as an additional broadleaf weed control option. A field experiment focused on crop safety was conducted in 2021, near Stuttgart, Arkansas, at the University of Arkansas System Division of Agriculture's Rice Research and Extension Center to evaluate the possibility of dicamba for use as an early season broadleaf material in rice. The experiment consisted of 2 factors: herbicide rate and application timing. Dicamba was applied in the form of Clarity® at 0.5 lb ae/ac (1x) and 1 lb ae/ac (2x) at 3 separate application timings [preemergence (PRE), 1-leaf, and 5-leaf growth stage]. Rice injury 2 weeks after the PRE application was 71% and 91% at a 1 and 2x rate, respectively. Applications made after PRE had less injury, as evident by 39% and 48% injury 2 weeks after the 1-leaf rice stage application at a 1 and 2x rate, respectively. The trend continues with the 5-leaf rice stage application, where the injury for a 1 and 2x rate was 8% and 12%, respectively. At 4 weeks after flood initiation, rice recovered to ≤5% injury, except for the PRE application at a 2x rate (33%). Based on these results, the severity of injury observed from early-season dicamba applications to rice would outweigh any benefits of broadleaf weed control. [ABSTRACT FROM AUTHOR]

Loyant herbicide technology is based on a new active ingredient--florpyrauxifen-benzyl, and offers broad-spectrum weed control. Previous research reported that Loyant provided effective control of troublesome weeds in rice production, such as barnyardgrass and hemp sesbania. Researchers also reported that the herbicide provided control of Palmer amaranth, a problematic weed, especially in furrow-irrigated rice systems. A field experiment was established in 2019 to evaluate the effect of soil moisture and herbicide applications that included florpyrauxifen-benzyl on weed control and crop safety. Results showed that the treatments tested did not cause visible injury during the season. All treatments, including Loyant, were very efficacious on barnyardgrass; and even at 48 days after treatment, control was greater than 94%. Loyant treatments also effectively controlled hemp sesbania. Average rough grain yield was 240 bu./ac in Loyant-treated plots, and no statistical differences were observed among the treatments. In conclusion, treatments using Loyant were not statistically influenced by soil moisture at application and provided effective weed control. According to these results, it is possible to include Loyant herbicide as a weed control option in non-flooded and flooded rice production systems. [ABSTRACT FROM AUTHOR]