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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]

The use of Enlist®, XtendFlex®, and LibertyLink® cropping systems are effective tools to facilitate weed management in cotton (Gossypium hirsutum L.). These technologies enable farmers to use 2,4-D, dicamba, or glufosinate over the top of cotton in season. However, the incidence of Palmer amaranth (Amaranthus palmeri S. Wats.) escapes demonstrates the importance of surveilling the spread of herbicide resistance. Therefore, this study aimed to evaluate herbicide resistance in Palmer amaranth accessions collected after glufosinate and auxin mimic herbicides (2,4-D or dicamba) were applied for weed control. A total of 22 accessions from eastern Arkansas were collected in the 2021 growing season. Herbicide treatments were equivalent to 0.5× or 1× rate of 2,4-D (Enlist One®) at 0.48 and 0.95 lb ae/ac, dicamba (XtendiMax®) at 0.25 and 0.5 lb ae/ac, and glufosinate (Liberty®) at 0.29 and 0.58 lb ai/ac, respectively. All treatments were applied to greenhouse-grown Palmer amaranth plants with 5 to 6 leaves, and 2 runs of 50 plants per accession were sprayed per treatment. Plant mortality (%) was assessed 21 days after treatment. Treatments with 2,4-D, dicamba, and glufosinate at 0.5× resulted in 80% or less mortality to 18, 13, and 6 accessions, respectively. Treatments with a 1× rate provided more than 80% control to all accessions treated with dicamba; meanwhile, only 18 and 21 accessions treated with 2,4-D and glufosinate, respectively, resulted in the same level of mortality. 2 accessions that resulted in less than 60% mortality after treatment with a 1× rate of 2,4-D were further evaluated, and resistance to 2,4-D was confirmed. These findings demonstrate the importance of monitoring weed survival in production fields. Implementing integrated weed management strategies to reduce selective pressure over current herbicide options could help mitigate herbicide resistance cases. [ABSTRACT FROM AUTHOR]

Resistance to glufosinate in Palmer amaranth (Amaranthus palmeri S. Wats.) was first reported in 2021 in Arkansas. Alternative chemical control methods are highly sought to avoid the spread of this problematic herbicide-resistant weed across the southern region of the United States. This study aimed to determine the effectiveness of herbicides labeled for preplant or preemergence applications in cotton (Gossypium hirsutum L.) and soybean (Glycine max L.) to control glufosinate-resistant Palmer amaranth. The preemergence (PRE) treatments were imazaquin (0.12 lb ai/ac), pendimethalin (1 lb ai/ac), diuron (1 lb ai/ac), metribuzin (0.67 lb ai/ac), flumioxazin (0.063 lb ai/ac), saflufenacil (0.045 lb ai/ac), fomesafen (0.25 lb ai/ac), trifludimoxazin (0.045 lb ai/ac), acetochlor (1.124 lb ai/ac), S-metolachlor (1.24 lb ai/ac), pyroxasulfone (0.129 lb ai/ac), and fluridone (0.15 lb ai/ac). Irrigation in the amount of 1 inch was applied after application to ensure the activation of herbicides. A postemergence (POST) treatment with glufosinate at 0.585 lb ai/ac was applied twenty days after preemergence treatments to confirm the presence of a glufosinate-resistant accession in the trial site. A randomized complete block design with 4 replicates was used with a nontreated control for comparison. Visual control (%) was rated, and aboveground biomass was collected 6 weeks after PRE treatments. Biomass reduction (%) was calculated in comparison to the nontreated control. The lowest visual control and biomass reduction were observed in treatments that received only glufosinate POST or imazaquin preemergence due to resistance to these herbicides. Low control and biomass reduction were also detected following the treatment with pendimethalin. Besides the herbicides mentioned above, visual control and biomass reduction rates were similar for all other herbicides. Although most of the tested herbicides provided acceptable Palmer amaranth control, overlapping multiple effective residual herbicides and POST-applied options are crucial to controlling glufosinate-resistant populations. [ABSTRACT FROM AUTHOR]

Arkansas rice (Oryza sativa L.) producers face challenges when transitioning to a furrow-irrigated rice (FIR) system, which lacks a continual flood to prevent weed emergence. The lack of a continual flood allows Palmer amaranth [Amaranthus palmeri (S.) Wats.] emergence throughout most of the growing season and creates an environment conducive for growth. The presence of Palmer amaranth in a FIR system may result in reduced rice yields and a greater need for additional herbicide applications. A field trial was conducted at the Milo J. Shult Agricultural Research and Extension Center in Fayetteville, Ark., during the 2022 growing season to assess the impact of Palmer amaranth on FIR. Newly emerged Palmer amaranth plants were marked every 7 days, beginning 1 week prior to rice emergence through 4 weeks after rice emergence. Palmer amaranth biomass decreased by 1.5 oz, on average, every 7 days that the emergence of the weed was delayed relative to rice. At 2 weeks after rice emergence and beyond, most Palmer amaranth plants failed to survive until rice harvest. Averaged over emergence times, female plants weighed more than male plants, which resulted in greater interference with rice for limited resources. Female Palmer amaranth plants that emerged one week prior to the emergence of rice produced 270,000 seeds per plant while Palmer amaranth plants that emerged the week after rice produced 11,000 seeds per plant. Palmer amaranth plants that emerged 1 week prior to rice reduced rough rice yield by 60% at 6 inches from the weed. These results show that Palmer amaranth emergence timing is a critical factor influencing rough rice yield potential, Palmer amaranth seed production, and Palmer amaranth biomass. [ABSTRACT FROM AUTHOR]

Furrow-irrigated rice (Oryza sativa L.), or row rice, has increased in acreage in Arkansas in the past few years. This practice allows growers to potentially grow rice on steeper ground that would require a vast number of levees that is labor and time intensive. However, this non-traditional rice growing method has a weed management drawback. The removal of the flood as a means of weed control places additional pressure on other weed management strategies and potentially different herbicide programs. Therefore, the objectives of this research were to determine if the manipulation of drill row spacing and bed width would influence season-long weed control. Two studies were seeded with hybrid rice RT7521 FP in 2021 and 2022 at Lonoke and Pine Tree, Ark. to evaluate treatments that consisted of three bed widths (30-, 38-, and 60-in.) and four drill row spacings (5-, 7.5-, 10-, and 15-in.). Barnyardgrass [Echinochloa crus galli (L.) P. Beauv.] density was assessed at the 5- to 6-leaf rice stage and preharvest. Canopy closure was captured with aerial digital images from a small, unmanned aircraft system (sUAS) collected at the 3-6 leaf and panicle differentiation rice stages. Rough rice yield was harvested with a plot combine and adjusted to 13% moisture. In general, barnyardgrass densities were lower across narrower drill row spacings (=7.5-in.) and bed widths (30-in.) early in the season; however, little differences were seen at the later preharvest timing. Canopy closure responded similarly as narrower drill row spacing and bed width had greater canopy closure. Rough rice yield was impacted less by drill row spacing and bed width, but narrower drill row spacing and bed width had a slightly higher numerical yield increase. Early findings suggest that a grower choosing this method of rice management should choose the narrowest drill row spacing allowed by their equipment and the narrowest bed widths that they can obtain to maximize weed management efforts. [ABSTRACT FROM AUTHOR]

In a flooded Arkansas rice system, producers and consultants identified the most problematic weed they face is barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.]. Due to the evolution of herbicide resistance and the overall hardiness of the weed, other control measures are needed for barnyardgrass in rice. The objective of this study was to evaluate the influence of rice cultivars and the manipulation of drill row width for barnyardgrass control in rice. Field experiments were conducted at the University of Arkansas System Division of Agriculture's Pine Bluff Small Farm Outreach Center, near Lonoke, Arkansas, Pine Tree Research Station, near Colt, Arkansas, and the Rohwer Research Station, near Watson, Arkansas in 2021 and 2022. The experiments were designed as randomized complete block split-plot designs (16 treatments) replicated 4 times with 4 nontreated controls for each drill width spacing. Each trial consisted of a whole plot factor of 4 drill row width spacings: 5, 7.5, 10, and 15 in. The subplot factor consisted of 4 cultivars: medium-grain inbred (CLM04), long-grain inbred (CLL16), long-grain hybrid (RT 7301), and FullPage long-grain hybrid (RT 7521 FP). Results indicated no interaction of drill row width spacing and rice cultivar for any response variables. A decrease in barnyardgrass density was observed for the 7.5-in. spacing compared to the 15-in. spacing across site-years for the 5- to 6-leaf (preflood) and preharvest rice stages. A 43% decrease in barnyardgrass density was observed for the hybrid cultivars compared to the inbred at the preharvest timing. Based on small unmanned aerial system (sUAS) imagery at panicle differentiation, there was a 20 percentage point decrease in canopy coverage from the 7.5 in. drill row width to the 15 in. width. This research provides insights on alternative weed management efforts through more precise drill row width spacing and cultivar selection in an Arkansas flooded rice system. [ABSTRACT FROM AUTHOR]

An increase in weedy rice (Oryza sativa L.) populations resistant to herbicides has heightened the need for alternative modes of action. Benzobicyclon is a 4-hydroxyphenylpyruvate dioxygenase inhibitor, the first of its kind labeled in rice. Benzobicyclon has shown substantial control of various monocot and broadleaf species, and this study evaluated the effectiveness of benzobicyclon as a weed control partner in imidazoline-resistant rice weed control systems. The study was organized as a split-plot in a randomized complete block design. The whole-plot factor was the presence or absence of benzobicyclon at 12.6 fl oz/ac applied post-flood, and the subplot factor was herbicide treatments containing imazamox and imazethapyr applied at either 2- to 3-leaf (early postemergence) or 5-to 6-leaf (preflood). Weedy rice and barnyardgrass (Echinochloa crus-galli) visual control, visual rice injury, and stunting evaluations were taken five times up to six weeks after post-flood treatment (WAFT). Rough rice yield was taken at crop maturity. Visual injury was minimal, never exceeding 12%, and there was no more than 8% injury due to bleaching. Improved visual weedy rice control was observed with the addition of benzobicyclon to 1) no additional herbicide, 2) imazamox at 5 fl oz/ac applied at 5- to 6-leaf rice, and 3) imazamox at 5 fl oz/ac applied post-flood. Rice yields were similar among all treatments. The findings from this research show that adding benzobicyclon to existing weed control programs in imidazoline-resistant rice can improve weedy rice control and aid in lowering weedy rice seedbank density. [ABSTRACT FROM AUTHOR]

Barnyardgrass and Palmer amaranth are difficult-to-control weeds in furrow-irrigated rice (FIR), especially as herbicide resistance continues to grow throughout the mid-South. The lack of flood in FIR considerably changes weed management for rice. Most growers that use only chemical weed management programs are looking for alternative methods to limit soil weed seedbank replenishment from escaped weeds. The objective of this experiment was to evaluate the use of a Redekop™ Seed Control Unit (SCU) as a non-chemical management strategy for harvest weed seed control (HWSC) of barnyardgrass and Palmer amaranth in FIR. The experiment was designed as a randomized complete block (550 by 25 ft) with eight replications, in Keiser, Ark., in 2022. The two treatments evaluated were harvesting with the Redekop SCU engaged or harvesting with the Redekop SCU disengaged, as would occur in a conventional harvest rice field. In plots where the Redekop SCU was used, seedbank replenishment was reduced by 69% and 83% for barnyardgrass and Palmer amaranth, respectively. Based on initial evaluations, the Redekop SCU could be an asset for rice producers. As HWSC methods become available for commercialization, additional parameters need to be further evaluated, specifically shattering of weed seed before crop harvest and the height distribution of seed on targeted weed species. Incorporation of HWSC may allow producers searching for a systems approach to better manage difficult-to-control weeds by diminishing the number of viable seeds returned to the soil-seedbank. [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]

Postemergence management of barnyardgrass [Echinochloa crus-galli (L.) P. Beauv] with evolution of resistance to acetyl-CoA carboxylase (ACCase) inhibitors is a challenging task. In a previous study, we confirmed several barnyardgrass accessions resistant metabolically to both the ACCase inhibitor cyhalofop-butyl (CyB; Clincher) and the synthetic auxin herbicide florpyrauxifen-benzyl (Loyant). The current study was performed to investigate effects of malathion (cytochrome P450 inhibitor) and/or 4-chloro-7-nitrobenzofurazan (NBD-Cl; glutathione S-transferase inhibitor) on metabolism of CyB in the resistant barnyardgrass accessions. Both malathion and NBD-Cl were not effective in restoring sensitivity of resistant barnyardgrass accessions to CyB (0.3 lb ai/ac). Rather, treatment with malathion followed by (fb) CyB antagonized the CyB's efficacy. Absorption of CyB in both CyB-susceptible (S) and resistant (R) barnyardgrass accessions was not influenced by malathion pretreatment. The consumption of CyB in S and R accessions decreased 1.5- to 10.5 times by pretreatment of malathion. However, production of cyhalofop-acid, the active herbicide form, was similar between treatments with CyB alone (1.8% to 17.3%) and treatments with malathion fb CyB (1.0% to 19.3%). Conclusively, malathion can antagonize CyB in barnyardgrass by contributing to reduced metabolism of CyB but not to its conversion to cyhalofop-acid. [ABSTRACT FROM AUTHOR]

Following the commercial launch of Loyant® (florpyrauxifen-benzyl) in 2018, occurrences of off-target movement of the herbicide were prevalent onto soybean [Glycine max (L.) Merr.] in proximity to rice (Oryza sativa L.). Field experiments were conducted in 2020 and 2021, in Fayetteville, Ark., to determine if Loyant-coated urea prills could mitigate damage to soybean from the herbicide in the instance of an off-target movement event in comparison to simulated spray drift. Seven low-dose rates of Loyant ranging from 0 to 3 fl oz/ac, were applied over the top of soybean at V3 as a foliar spray or coated urea and evaluated for visible injury at 7, 14, 21, and 28 days after treatment (DAT). In addition to visible injury, soybean yield was collected at harvest. A Weibull Growth curve (R2 = 0.99) was used to model visible injury at 21 DAT, and a Logistic 3P curve was fit for relative grain yield following harvest (R2 = 0.85), both as a function of herbicide rate. Additionally, a Logistic 3P model was used to regress the relationship between visible injury and relative soybean yield (R2 = 0.86). The predicted (a = 0.05) Loyant dose needed to elicit 80% visible injury to soybean from a coated or foliar application was 9.8 and 0.3 fl oz/ac, respectively, which was a 33-fold increase in soybean sensitivity when foliar spray drift occurs. At the maximum tested rate of Loyant (3 fl oz/ac), 100% of soybean yield was protected when the herbicide was coated on urea (54 bu./ac) in contrast to simulated spray drift (2 bu./ac). In areas where soybean is adjacent to rice, applications of Loyantcoated urea will likely mitigate injury to soybean as opposed to spray drift of the herbicide. [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]

Resistance to quizalofop-p-ethyl is the newest herbicide tolerance technology in rice fields. This technology provides resistance to the herbicides Provisia® and Highcard™ and adds a new mode of action for weedy rice control to the rice weed control portfolio. However, using additional chemistries is essential to ensure the prolonged viability of this technology and avoid weed resistance. Therefore, this study evaluated how benzobicyclon (Rogue®) fits into a Max-Ace® rice system where Highcard is used for weedy rice (Oryza spp.) and barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] control. The experiment was conducted in 2022 in Stuttgart, Arkansas, and organized in a two-factor randomized complete block with a split-plot setup. The whole-plot factor was with or without benzobicyclon postflood (POSTF), and the sub-plot factor was herbicide programs: 1) no herbicide, 2) quizalofop sprayed at early postemergence (EP) and preflood (PREF), 3) quizalofop sprayed at EP and POSTF, 4) quizalofop sprayed at PREF, and 5) quizalofop sprayed at POSTF, respectively. Weedy rice and barnyardgrass control was visually rated 4 weeks after POSTF treatments. Rough rice yields were obtained at the end of the season. For both weeds evaluated, the lowest control levels were obtained when quizalofop was only sprayed POSTF without benzobicyclon. Barnyardgrass and weedy rice control were above 95% whenever repeated herbicide applications of quizalofop were present, independently of benzobicyclon. The lowest yield was obtained in the treatment with a single application of quizalofop POSTF. The highest yields were obtained when treatments included benzobicyclon POSTF, or when quizalofop was sprayed twice in the season without benzobicyclon. The alliance of Max-Ace rice systems with an alternative herbicide like benzobicyclon is a potent weed control option to reduce the development of herbicide resistance throughout the years. [ABSTRACT FROM AUTHOR]

Diflufenican is a new herbicide to be labeled, potentially, for soybean [Glycine Max (L.) Merr] production in the United States. Diflufenican is an Herbicide Resistance Action Committee/Weed Science Society of America group 12 herbicide, the first group 12 herbicide labeled for use in soybean production. Soybean producers need new chemistries to help control Palmer amaranth (Amaranthus palmeri S. Wats.). Palmer amaranth has evolved resistance to 9 modes of action; therefore, diflufenican is being evaluated for its control. Two field experiments were conducted at the University of Arkansas System Division of Agriculture's Milo J. Shult Agricultural Research and Extension Center in Fayetteville, Arkansas, to evaluate the tolerance of soybean and associated weed control with various rates and application timings of the diflufenican mixture. For the tolerance trial, the diflufenican mixture was applied at 1 and 2 times the anticipated 1X labeled rates at 14- and 7-day preplant, preemergence, and 3 days after planting (DAP). The diflufenican mixture was applied 14- and 7-day preplant, preemergence, and 3 DAP at a 1X labeled rate for the weed control trial. Injury 14 DAP ranged from 2% to 20% for the 1X rate of the herbicide and 6% to 32% for the 2X rate. By 28 DAP, injury decreased for both herbicide rates, with the most injury being observed at the 3 DAP application timing for both rates. Grain yield was collected at maturity, and no difference was observed between application timings and herbicide rates. Palmer amaranth and common lambsquarters (Chenopodium album L.) control was greater than 97% for all application timings, except the 14-day preplant timing 21 DAP. By 42 DAP, the application timing of preemergence and 3 DAP provided greater than or equal to 90% control of the 2 weeds. Grain yield increased the closer the herbicide application was made to planting and soybean emergence due to improved weed control. [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]

Glufosinate is a commonly used postemergence herbicide to control weeds in glufosinate-resistant cropping systems. Recently, glufosinate resistance was detected in Palmer amaranth (Amaranthus palmeri S. Wats.) accessions from Arkansas, and the amplification and overexpression of chloroplastic glutamine synthetase enzyme (GS2) was confirmed to be the resistance mechanism in one resistant population. It is uncertain when this variation in the gene occurred, and this study aimed to verify if the GS2 copy number has increased over the years across Palmer amaranth populations with reduced susceptibility to glufosinate compared to accessions collected in 2001. Ten accessions from 2001 (A-01) and 13 accessions collected in 2020 or 2021 (A-20) were selected for this experiment. Seventy-five plants per accession were sprayed with glufosinate at 0.51 lb ai/ac to assess mortality. Gene copy number assay was conducted with DNA extracted from nontreated plants from A-01 and glufosinate survivors from A-20 accessions. Three biological replications were extracted for each accession, and each sample was assessed twice in each primer pair. Gene copy number was calculated relative to the Palmer amaranth reference gene. Glufosinate mortality decreased when comparing Palmer amaranth populations from 20+ years ago to those recently collected. All A-20 accessions tested had at least 3 survivors, while A-01 accessions had 100% mortality. Three clusters were formed with the mortality data. Cluster 1 comprised accessions with high mortality (96% to 100%) and included 2 A-20 accessions and all A-01 accessions. The other clusters only included A-20 accessions; mortality ranged from 82% to 93% and 52% to 68% in clusters 2 and 3, respectively. No significant difference was detected for gene copy number among the accessions when grouped by collection year. These results indicate that increased glufosinate tolerance is due to an unidentified mechanism(s), and additional investigations are necessary. [ABSTRACT FROM AUTHOR]

Resistance mechanisms to trifluralin have been explored in a Palmer amaranth (Amaranthus palmeri S. Watson) accession collected in eastern Arkansas. However, gene expression has not yet been studied. Thus, the objective of this research was to describe the basal gene expression levels of the a- and ß-tubulin genes in a trifluralin-resistant Palmer amaranth accession. Basal gene expression levels of the a- and ß-tubulin genes were measured relative to Cinnamoyl-CoA reductase (CCR) and peter Pan-like (PPAN) in non-treated tissue of both resistant and susceptible Palmer amaranth accessions. Results demonstrated that the basal expression levels found in both the a- and ß-tubulin genes were in the range of 0.4-1.0-fold. No significant differences were found between the resistant and susceptible accessions in either of the reference genes used. These results further corroborate the presence of nontarget site resistance mechanisms in this trifluralin-resistant accession collected in eastern Arkansas. [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 is widely used in the mid-South to control Palmer amaranth [Amaranthus palmeri (S.) Wats] in soybean and can cause severe injury and yield loss if a highly sensitive soybean 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 2021 to evaluate current soybean varieties and their tolerance to a labeled rate of soil-applied metribuzin. Injury, which was evaluated at 21 and 28 days after treatment (DAT), showed that nearly 37% of the tested varieties showed adequate field tolerance. Forty-seven percent of the tested varieties showed injury symptoms and were labeled moderately tolerant to the herbicide. The remaining 16% of the varieties screened exhibited severe injury when treated with a full rate of metribuzin. Therefore, regardless of the herbicide technology chosen by a grower, there are sufficient varieties that allow metribuzin to be integrated at a full rate into weed control programs that focus on controlling Palmer amaranth. [ABSTRACT FROM AUTHOR]

A field experiment was conducted in 2021 to evaluate the preemergence activity of metribuzin (group 5) and pyroxasulfone (group 15) herbicide combinations in the control of several weed species and to determine their effectiveness as preemergence options in soybean [Glycine max (L.) Merr.] weed management systems. All treatments provided nearly ideal control of Palmer amaranth [Amaranthus palmeri (S.) Wats.] (99%), pitted morningglory [Ipomoea lacunosa (L.)] (better than 95%), and prickly sida [Sida spinosa (L.)] (better than 97%) by 35 days after preemergence application (DA PRE). No significant impact of preemergence treatments was observed on stand loss. Overall, preemergence treatments resulted in less than 6% chlorosis and necrosis by 35 DA PRE. Additionally, only treatments with Glory® at 1.25 lb/ac (metribuzin) or 5.75 fl oz/ac of Zidua® (pyroxasulfone) plus Glory at 1.25 lb/ac resulted in 7% and 5% of crop stunting, respectively, by 35 DA PRE. In contrast, other treatments resulted in less than 1% visible stunting. Therefore, all herbicide treatments tested resulted in desirable weed control and minimal impact on early crop development. Utilizing a combination of herbicide sites of action could minimize the expansion of herbicide resistance. Generally, preemergence treatments do not provide robust weed control persisting for the entire critical weed-free period of soybean (from emergence to V4). Therefore, timely postemergence applications should be recommended to reduce possible yield impacts. [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]

Drought events are predicted to increase in the future. Evaluating the response of herbicide-resistant and -susceptible weed ecotypes to progressive drought can provide insights into whether a resistance trait affects the fitness of resistant weed populations. Two experiments were conducted in a greenhouse between January and May 2021 to evaluate drought tolerance differences between Palmer amaranth (Amaranthus palmeri S. Wats.) accessions resistant to S-metolachlor (Dual Magnum®) or glyphosate (Roundup PowerMax™ II) and their susceptible counterparts. The accessions used were: S-metolachlor-resistant (17TUN-A), a susceptible standard (09CRW-A), and glyphosate-resistant and glyphosate-susceptible plants from accession 16CRW-D. The daily transpiration of each plant was measured. The daily transpiration rate was converted to normalized transpiration ratio (NTR) using a double-normalization procedure. The daily soil water content was expressed as a fraction of transpirable soil water (FTSW). The threshold FTSW (FTSWcr), after which NTR decreases linearly, was estimated using two-segment linear regression analysis. A greater FTSWcr means early stomatal closure with respect to the initiation of water deficit. The data showed differences between S-metolachlor-resistant and -susceptible accessions (P = 0.05). The FTSW remaining in the soil at the breakpoint for the S-metolachlor-susceptible accession (09CRW-A) was 0.17 ± 0.007. The FTSW remaining in the soil at the breakpoint for the S-metolachlor-resistant accession (17TUN-A) was 0.23 ± 0.004. The FTSW remaining in the soil at the breakpoint for the glyphosate-resistant and glyphosate-susceptible plants (16CRW-D) were 0.25 ± 0.007 and 0.25 ± 0.008, respectively. Although the mechanism endowing resistance to S-metolachlor might have contributed to increased drought tolerance, follow-up experiments are needed to verify this finding. Increased EPSPS copy number did not improve drought tolerance of Palmer amaranth. As droughts are predicted to increase in frequency and severity, these results suggest that S-metolachlor-resistant and glyphosate-resistant Palmer amaranth populations will not be at a competitive disadvantage compared to susceptible genotypes. Alternative and diverse management strategies will be required for effective Palmer amaranth control regardless of herbicide resistance status. [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]

Palmer amaranth [Amaranthus palmeri (S.) Wats.] is one of the most troublesome soybean weeds [Glycine max (L). Merr.]. Chemical control options are limited with the evolution of resistance to 9 herbicide sites of action (SOAs) in Palmer amaranth. In 2021, a greenhouse experiment was conducted at the University of Arkansas System Division of Agriculture's Milo J. Shult Agricultural Research and Extension Center in Fayetteville, Ark., to evaluate the response of Arkansas Palmer amaranth populations to commonly used row crop herbicides with differing SOAs. Two experimental runs were conducted as a completely randomized design with 3 spatial replications. Three difficult-to-control accessions (A2019, A2020, and B2020) along with 1 standard susceptible accession (SS2001) were treated with 10 different herbicide SOAs, including pendimethalin and S-metolachlor as a preemergence application and imazethapyr, 2,4-D, dicamba, atrazine, diuron, glyphosate, glufosinate, fomesafen, paraquat, mesotrione, and tembotrione as a postemergence application. All difficult-to-control accessions were observed to have at least 20 percentage points less mortality than a susceptible standard to 5 herbicide SOAs. Mortality of A2019 accession was at least 20 percentage points less than the susceptible standard to herbicides from 9 differing SOAs. Additionally, A2020 and B2020 showed reduced sensitivity to 5 herbicide SOAs. Furthermore, atrazine and paraquat provided >86% mortality and are still viable options for controlling challenging Palmer amaranth populations. [ABSTRACT FROM AUTHOR]

Resistance to glufosinate in Palmer amaranth [Amaranthus palmeri (S.) Watson] was first reported in 2021 in Arkansas, and evaluating alternative control options for these resistant populations is a high priority. Enhanced herbicide detoxification by glutathione S-transferase (GST) enzymes is one of the possible resistance mechanisms responsible for glufosinate resistance. Therefore, experiments were designed to evaluate if adding a GST-inhibitor would overcome glufosinate resistance in Palmer amaranth and quantify the number of chloroplastic glutamine synthetase (GS2) gene copies present in resistant plants. Seedlings of the resistant (20-59) and susceptible (SS) accessions were transplanted into a field at the University of Arkansas System Division of Agriculture's Milo J. Shult Agricultural Research and Extension Center in Fayetteville, Ark. The treatments were glufosinate applied at 10 a.m., glufosinate at 10 p.m., and glufosinate + GST-inhibitor [NBD-Cl (4-chloro-7-nitrobenzofurazan)] at 10 p.m. The total number of plants per accession in each plot was counted prior to and 2 weeks after application to calculate mortality (%). Concomitantly with the field experiment, a gene copy number assay was conducted with DNA extracted from nontreated plants from 2 different susceptible accessions and glufosinate survivors from accession 20-59. GS2 copy number was calculated relative to 2 standard genes. Overall, mortality was 17% and 97% for 20-59 and SS, respectively. Mortality did not differ among treatments. Relative to 2 reference genes, the gene copy number in the resistant accession was significantly higher than the susceptible tested. The resistant accession had 85 and 86 copies, while the 2 SS accessions had an average of only 2 GS2 copies. An increase in the chloroplastic glutamine synthetase copy number in the resistant plants enables the production of enough enzymes to survive glufosinate, which explains why the addition of a GST-inhibitor had no impact on the control of glufosinate-resistant Palmer amaranth. [ABSTRACT FROM AUTHOR]

The commercial launch of florpyrauxifen-benzyl (Loyant™) in 2018 was followed by observed soybean [Glycine max (L.) Merr.] injury due to off-target movement of the herbicide. Hence, a field experiment was conducted in 2020 and 2021 in Fayetteville, Arkansas, to evaluate soybean injury following low rates (0 to 0.094 oz ai/ac) of florpyrauxifen-benzyl applied either as a liquid spray or coated on urea at the V3 growth stage. In both years, soybean response was evaluated at 21 days after applications of florpyrauxifen-benzyl were made to drill-seeded (7-in. rows) soybean. In both years, the greatest soybean injury (100%) was observed following sprayed applications of florpyrauxifen-benzyl at 0.094 oz ai/ac. However, when florpyrauxifen-benzyl was coated on urea at 0.094 oz ai/ac, only 24% and 19% visual soybean injury was observed in 2020 and 2021, respectively. Regardless of year, coating florpyrauxifen-benzyl on urea was less injurious to soybean when compared to sprayed applications at every herbicide rate and rating timing. Likewise, no deleterious effect on yield was observed when florpyrauxifen-benzyl was coated on urea, but all sprayed applications negatively impacted yield. Overall, coating florpyrauxifen-benzyl on urea reduced soybean injury by 68 to 94 and 64 to 92 percentage points at 21 days after treatment in 2020 and 2021, respectively. Coating florpyrauxifen-benzyl on urea appears to substantially reduce soybean injury and the risk of an off-target movement occurrence. Future research is needed to establish the effectiveness of this application technique on weed control. [ABSTRACT FROM AUTHOR]

In recent years, johnsongrass (Sorghum halepense) escapes and infestations have been a growing issue for cotton (Gossypium hirsutum) producers across the mid-South. This could be due to reliance on specific herbicides such as glyphosate and acetyl CoA carboxylase inhibitors. A greenhouse study was conducted in Fayetteville, Arkansas, 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 six counties in eastern Arkansas. These accessions were then 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. Quizalofop was the only herbicide that provided 100% mortality of all accessions. Some plants escaped fluazifop, but all accessions had greater than 90% mortality, except one accession from Crittenden County. Glyphosate resulted in variable levels of mortality, ranging from 10% to 100%. Overall, Arkansas johnsongrass accessions showed high levels of variability in control when treated with glyphosate, while fluazifop and quizalofop applications appeared effective on almost all of the accessions tested. [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]

Weedy rice in Arkansas is resistant to HRAC/WSSA group 1 and 2 herbicides that are commonly used for control. The ROXY® Rice Production System (RRPS) provides tolerance to herbicides containing oxyfluorfen. Oxyfluorfen is a Herbicide Resistance Action Committee/Weed Science Society of America (HRAC/WSSA) group 14 herbicide labeled for preemergence (PRE) and postemergence (POST) applications in many crops. Oxyfluorfen currently is not labeled for use in rice; however, the Roxy trait in the RRPS allows for applications of the herbicide. During the 2021 and 2022 growing seasons, two independent field trials were conducted at the University of Arkansas System Division of Agriculture's Rice Research and Extension Center near Stuttgart, Ark. The first experiment was designed to determine if there was a rate response for weedy rice control associated with oxyfluorfen applied POST at the 2-leaf growth stage of weedy rice. The second experiment was designed to determine the optimal rate of oxyfluorfen to use PRE and POST in a sequential program when the maximum annual rate could not exceed 1.5 lb ai/ac. For the rate response experiment, oxyfluorfen (ALB2024) was POST-applied at 0.5, 0.75, 1, 1.25, or 1.5 lb ai/ac when the weedy rice reached the 2-leaf growth stage. In the sequential application experiment, mixtures of clomazone and oxyfluorfen (ALB2023) (0.3 plus 0.5, 0.75, or 1 lb ai/ac, respectively) were applied PRE, followed by a POST application of oxyfluorfen that resulted in the total amount of the herbicide applied being 1.5 lb ai/ac. Weedy rice control for all treatments ranged from 57 to 73% for the rate response experiment at 35 days after treatment. In the sequential application experiment, oxyfluorfen applied PRE resulted in 46 and 70% weedy rice control at the lowest (0.5 lb ai/ac) and highest (1 lb ai/ac) oxyfluorfen rates, respectively. At 14 days after the final treatment, 78 to 81% weedy rice control was observed for all treatments when oxyfluorfen was applied sequentially. Oxyfluorfen could potentially serve to suppress weedy rice in a RRPS; however, oxyfluorfen alone will not be able to achieve complete control. [ABSTRACT FROM AUTHOR]

Widespread herbicide resistance is an issue in rice (Oryza sativa L.) due to the difficult control of the resistant weeds, making weed management challenging for farmers. Therefore, research of new modes of action to control herbicide-resistant weeds must also include evaluations of crop safety. Fluridone was tested for potential weed control in rice; however, little is known regarding the optimum application timing to reduce crop response. Therefore, this study aimed to evaluate the influence of fluridone application timing on rice tolerance. The experiment was conducted in 2022 at the University of Arkansas System Division of Agriculture's Rice Research and Extension Center near Stuttgart, Ark. The experiment was organized as a randomized complete block with 10 application timings and 4 replications. The application timings were: 22 and 11 days preplant, preemergence (PRE), delayed-preemergence (DPRE), 1-leaf, 2-leaf, 3-leaf, 4-leaf, preflood, and immediately after flood establishment (post-flood). Nontreated control plots were included for comparison. Fluridone was applied at 0.15 lb/ac in all treatments. Visual rice injury and ground cover were collected 35 and 70 days after emergence (DAE), and rough rice yield was collected at maturity. At 35 DAE, PRE and DPRE treatments caused 13% and 11% visible injury, respectively. However, by 70 DAE, crop injury increased following the establishment of the flood, reaching 40% for both the PRE and DPRE treatments. Canopy loss occurred at 35 and 70 DAE for the PRE treatment compared to the nontreated control. Rice exhibited a high tolerance level to a post-flood fluridone application, comparable to the nontreated control. However, at the application timings PRE, DPRE, and 1-leaf, rough rice yield was lower than in plots where fluridone was not applied. Further research on rice tolerance to fluridone is needed over a wide range of environments as well as quantifying the weed control value of fluridone in drill-seeded rice culture. [ABSTRACT FROM AUTHOR]

ProvisiaTM and Max-AceTM rice, Oryza sativa L., are two options available to producers that enable the use of quizalofop for barnyardgrass and weedy rice control among other grass weeds. The HighcardTM formulation of quizalofop is labeled for use on Max-AceTM rice while the ProvisiaTM formulated product is labeled for use on ProvisiaTM rice. ProvisiaTM and HighcardTM formulations differ in that the latter also contains isoxadifen to help safen the herbicide in Max-AceTM rice. Weed control and crop tolerance were evaluated at the Rice Research and Extension Center near Stuttgart, Arkansas to compare HighcardTM-based herbicide programs in Max-AceTM rice to a standard ProvisiaTM program in ProvisiaTM rice. For both technologies, long-grain, inbred cultivars were drill-seeded at recommended densities. Both rice technologies included sequential applications of ProvisiaTM or HighcardTM with ZuraxTM in the first postemergence application and VopakTM in the second application (preflood). Two additional programs in Max-AceTM rice included the addition of ZuraxTM and Permit PlusTM or VopakTM and StamTM at early postemergence and preflood applications, respectively. ProvisiaTM rice was injured 17% by ProvisiaTM herbicide at 3 weeks after final treatment (WAFT), whereas rice injury in the HighcardTM programs ranged from 1% to 6% at the same evaluation. Weedy rice, Oryza sativa L., control was greater than 95% in all treatments at 4 WAFT. Barnyardgrass, Echinochloa crus-galli (P.) Beauv., control exceeded 99% at 4 WAFT for all herbicide treatments. Rough rice yields were similar among all herbicide treatments, regardless of rice technology. These findings show that timely applications of HighcardTM in Max-AceTM rice result in end-of-season weedy rice and barnyardgrass control levels comparable to those in a ProvisiaTM rice system. [ABSTRACT FROM AUTHOR]

Barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] is a highly problematic weed in flooded rice (Oryza sativa L.) that can result in significant yield losses when left unchecked. New methods of barnyardgrass control will be needed to preserve high yields in Arkansas rice production. S-metolachlor is a chloroacetamide herbicide that provides residual control of grasses and small-seeded broadleaf weeds. An experiment was conducted in Keiser, Ark. to evaluate the efficacy of S-metolachlor in a rice system in conjunction with a fenclorim seed treatment to mitigate the risk of crop injury. Three rates of S-metolachlor (0.5, 1.0, and 1.5 lb ai/ac) were applied delayed-preemergence to 'Diamond' rice that was treated with fenclorim at 0 or 2.5 lb of ai/1000 lb-seed. Visual injury to rice and visual control of barnyardgrass were rated in comparison with the nontreated control and were evaluated throughout the season. Rough rice yield was evaluated after harvest. While visual rice injury was higher on average in the first two weeks after treatment without fenclorim, by 28 days after treatment (DAT) the low rate of S-metolachlor combined with a fenclorim seed treatment caused less than 17% injury. S-metolachlor provided effective visual control of barnyardgrass at all three rates up to 28 DAT that exceeded 90% control. Overall, the presence of fenclorim reduced injury to rice at each rate of S-metolachlor, while not having an impact on weed control. At a rate of 0.5 lb ai/ac of S-metolachlor with a fenclorim seed treatment, rice yield was comparable with the nontreated control. However, increasing rates of metolachlor reduced yield. If S-metolachlor becomes labeled for use in rice, this will provide an alternative site of action for weed control without requiring a herbicide resistance trait. [ABSTRACT FROM AUTHOR]

Arkansas rice producers have noticed an increase of resilient barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] becoming increasingly difficult to control. Cultural methods of drill width spacing manipulation and nozzle selection aid in controlling this hardy weed. The objective of this study was to evaluate the influence of nozzle type and rice drill width spacing on spray coverage and weed control in rice. Experiments were conducted at the University of Arkansas at the Pine Bluff Small Farm Outreach Center near Lonoke, Arkansas and the University of Arkansas System Division of Agriculture's Pine Tree Research Station near Colt, Arkansas, in 2021. Each plot was drill-seeded with four drill width spacings: 5, 7.5, 10, and 15 inches. Two herbicide applications were made with commonly used rice herbicides with 5 types of nozzles: XR, AIXR, TTI, TTI60, and AITTJ60, of which, the TTI60 and AITTJ60 were dual-fan nozzles. Barnyardgrass density counts were assessed at the 3-leaf rice stage and prior to harvest. Water-sensitive cards were placed and sprayed at the preflood stage to assess the percent spray coverage of each nozzle type. Both experiments showed no differences between the interaction of drill width spacing and nozzle types for any response variables. At the Lonoke location, barnyardgrass density was greater at 15-in. spacing than the 5-, 7.5-, and 10-in. spacing at the 3-leaf rice stage. The smaller droplet-sized nozzles (XR, AITTJ60, AIXR) produced a greater percent spray coverage than the larger droplet-sized nozzles (TTI60 and TTI), but no increase in coverage was observed from dual-fan nozzles. This research provided insights on a more precise drill width spacing and nozzle type selection to be used in rice standard practices. [ABSTRACT FROM AUTHOR]

Managing emerged weeds that have evolved resistance to herbicides is a challenging task. From dose-response experiments conducted previously, we selected barnyardgrass [Echinochloa crus-galli (L.) P. Beauv] biotypes susceptible (S) and resistant (R) to three aryloxyphenoxypropionate herbicides, namely cyhalofop-butyl (CyB; Clincher), fenoxaprop-ethyl (FeE; Ricestar HT), and quizalofop-ethyl (QuE; Provisia). For these barnyardgrass biotypes, absorption, translocation, and metabolism of CyB and QuE were evaluated to confirm the presence of a non-target-site resistance mechanism. Absorption, translocation, and total metabolism of tested herbicides were similar for S and R biotypes. Significant differences between S and R barnyardgrass were observed in the production of active acid forms of each herbicide (cyhalofop-acid and quizalofop-acid). Production of cyhalofop-acid was less in R barnyardgrass (3% to 8%) for 24 h after herbicide application than in the S barnyardgrass (8% to 16%). Meanwhile, the production of quizalofop-acid was less in R barnyardgrass (0% to 14%) throughout the study period than in the S barnyardgrass (3% to 22%). Overall results show that a non-target-site resistance mechanism altering the production of acid herbicide forms may contribute at least partly to the resistance of the tested barnyardgrass biotypes to CyB and QuE. [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]

Provisia (quizalofop-resistant) rice technology became commercially available for Mid-south growers in 2018 and was followed by injury to Provisia cultivars from postemergence applications of quizalofop. Rice is grown in close association with glyphosate-resistant corn, cotton, and soybean, increasing the risk of injury to rice through glyphosate drift. Field experiments were conducted in 2021 at Colt and Keiser, Arkansas, to determine if a sublethal rate of glyphosate interacts with sequential quizalofop applications to increase the risk for injury to Provisia rice cultivar PVL02 compared to applications of quizalofop alone. Experiments were implemented as a split-plot design, with location as a whole-plot factor and herbicide treatment (glyphosate followed by initial quizalofop application at 10-, 7-, 4-, and 0-day intervals and glyphosate applied alone at the same 10-, 7-, 4-, and 0-day intervals) as a split-plot factor. Glyphosate was applied at 0.08 lb ae/ac, 1/12.5X of the labeled use rate in soybean, and sequential quizalofop applications were at the recommended use rate of 0.1 lb ai/ac applied at the 2-leaf stage, followed by the 5-leaf stage. At 28 days after treatment (DAT), glyphosate followed by initial quizalofop at 0-day interval caused 19 percentage points more injury than glyphosate applied alone at the 0-day interval regardless of location. In addition, glyphosate followed by quizalofop at the 0-day interval had a higher glyphosate concentration in leaf tissue samples than glyphosate applied alone at the 0-day interval when sampled at 7 days after treatment for both locations. Furthermore, rough rice grain yield was reduced by 34 percentage points when glyphosate application was followed by quizalofop application at 0-day interval compared with glyphosate applied alone at Colt, Arkansas. Overall, glyphosate followed by quizalofop applications exacerbates injury over sequential quizalofop application alone or glyphosate exposure alone, and as the timing interval between exposure to sublethal glyphosate and quizalofop application shortens, the detrimental effect on Provisia rice increases. [ABSTRACT FROM AUTHOR]

Weeds compete with rice for resources, and suboptimal management can result in significant yield losses. Proper weed seedling identification with adequate herbicide application timeliness are required to develop effective weed control strategies. With a gradually decreasing barrier to entry, stakeholders are gaining interest in using drone remote sensing to facilitate scouting and optimize strategic planning. However, remote rice weed detection presents unique challenges, and rice growers will only fully benefit from available technologies if provided with decision-support systems that meet their specific needs. Often, assumptions are made on the type and quality of information that can be extracted from drone images without proof that such data can, in fact, be collected. The objective of this study was to determine if rice weed seedlings could be identified in raw drone images collected before flood. Remote sensing and ground-truth data were collected in 6 locations with different weed species, rice growth stages, and weed seedling sizes. Weed seedlings were counted in the field and in drone images collected at different flight altitudes. Data were analyzed to compare the number of weed seedlings seen in the drone images to the number of weed seedlings found in the field. Results demonstrated that it was not always possible to distinguish all rice weed seedlings in the collected images independently from image resolution. When possible, drone images needed to be collected at a very low altitude (less than 5 ft) using typical prosumer drone remote sensing equipment. The findings provided a better understanding of the possibilities and limitations of drone remote rice weed seedling detection. [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]

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, a field experiment was conducted in 2020 and 2021 in Fayetteville, Arkansas, to evaluate soybean injury following low rates (0 oz ai/ac to 0.094 oz ai/ac) of florpyrauxifenbenzyl applied either as a foliar spray or coated on urea at the V3 stage. During both years, the response of soybean was evaluated when florpyrauxifen-benzyl was applied in a wide-row (36 in.) system at 7, 14, 21, and 28 days after application. In both years, 100% soybean injury (death) occurred following foliar spray applications. However, when coated on urea, the maximum soybean injury from florpyrauxifen-benzyl at 0.094 oz ai/ac resulted in only 20% and 23% soybean injury in 2020 and 2021, respectively. At all timings, equivalent rates of florpyrauxifen-benzyl coated on urea caused less injury than that of the foliar spray applications. No deleterious effect on yield was observed in 2020 and 2021 from any florpyrauxifen-benzyl coated on urea treatment when compared to the nontreated plots, but all foliar spray treatments caused a negative effect on yield. Overall, florpyrauxifen-benzyl coated on urea reduced soybean injury by 50 to 91 and 55 to 96 percentage points in 2020 and 2021, respectively, across all rating dates when compared to foliar spray applications. Coating florpyrauxifenbenzyl onto urea appears to substantially reduce the risk for off-target movement of the herbicide onto soybean, and future research needs to establish the effectiveness of this application technique on weed control. [ABSTRACT FROM AUTHOR]