Barnyardgrass Control Research Articles

Clomazone and Oxyfluorfen Combinations in a Flooded Rice System

Abstract Rice producers battle herbicide-resistant weeds worldwide while producing rice for ≥50% of the world’s population. Oxyfluorfen can provide rice producers with an alternative site of action for barnyardgrass control, as there are no documented cases of grass weeds being resistant to the herbicide in the midsouthern United States. Oxyfluorfen is anticipated to be labeled in the Roxy Rice Production System and may be sold as a clomazone:oxyfluorfen premixture; hence, experiments were conducted in 2021 and 2022 to evaluate preemergence-applied clomazone:oxyfluorfen ratios compared to clomazone alone on silt loam and clay soils. All ratios of the herbicides caused less than 7% injury to rice in two of four site-years on silt loam soils, whereas, in the two other site-years, the mixtures caused 10% to 40% rice injury at all observation timings. All combinations of the two herbicides provided at least 73% barnyardgrass control 5 weeks after rice emergence (WAE) in three of the four site-years on silt loam soils. In at least two of four site-years at 1 and 3 WAE, barnyardgrass control was improved when oxyfluorfen was added to clomazone compared to clomazone alone. On clay soil, barnyardgrass control in both site-years was ≥77% at 5 WAE for all clomazone and oxyfluorfen ratios. Injury to rice ranged from 13% to 30% for all treatments containing clomazone and oxyfluorfen in one of two site-years on clay soil at all observation timings. At 7 WAE, contrasts indicated that the 1:3 ratio of clomazone to oxyfluorfen provided greater barnyardgrass control than the 1:1.5 and 1:2 ratios in one of two site-years. Based on these findings, oxyfluorfen would improve the consistency of barnyardgrass control over clomazone alone in some instances. However, there is an increased risk of injury to rice with the addition of oxyfluorfen.

Oxyfluorfen use in Combination with Clomazone or Quinclorac

Abstract Oxyfluorfen, a Herbicide Resistance Action Committee (HRAC)/Weed Science Society of America (WSSA) Group 14 herbicide that inhibits protoporphyrinogen IX oxidase, has shown significant potential in controlling barnyardgrass. Despite its current lack of labeling for use in midsouthern U.S. rice due to the potential for crop injury, the introduction of a trait in rice that confers resistance to oxyfluorfen could provide producers with an effective alternative site of action for weed control. Field experiments were conducted during the 2021 and 2022 growing seasons near Stuttgart, AR, and near Lonoke, AR, to determine the optimum rates of clomazone (280 or 336 g ha-1) and oxyfluorfen (673 or 840 g ha-1) to use in sequential preemergence (PRE) and postemergence (POST) applications on a silt loam soil and to assess the efficacy of oxyfluorfen when combined with clomazone and quinclorac PRE, followed by oxyfluorfen POST. No differences in barnyardgrass control were observed among treatments 14 days after emergence (DAE) in three site years, as all control was ≥90%. By 35 days after the postemergence application (DAPOST), all barnyardgrass control was ≥94% for herbicide treatments in all site years. All herbicide treatments resulted in lower barnyardgrass seed production than the nontreated in 2021. Contrasts revealed that oxyfluorfen applied PRE on a silt loam soil resulting in barnyardgrass control similar to clomazone or quinclorac alone at 14 DAE. Although oxyfluorfen combined with clomazone or quinclorac did not increase barnyardgrass control, an additional site of action for control of this weed could help reduce the evolution of resistance. Mixing oxyfluorfen with clomazone in a dry-seeded rice production system in the midsouthern U.S. would effectively control barnyardgrass and reduce the risk for resistance to both herbicides, further highlighting the potential of oxyfluorfen in rice production.

Cultivo de soja em área de arroz irrigado para reduzir a infestação de plantas daninhas

ABSTRACT Lowland rice in Santa Catarina (SC), Brazil, is grown as a sole crop, which has aggravated problems with weeds. In this context, the objective of this study was to evaluate the efficacy of weed management systems in soybean crops to decrease weed infestation in lowland rice production areas, using pre- and post-emergence herbicides. The experiment was conducted in Turvo, SC, from August 2021 to April 2022. A randomized block design with four replications was used, in a 6 × 5 factorial arrangement. The factors consisted of six pre-emergence herbicides treatments (S-metolachlor, diclosulam, sulfentrazone, sulfentrazone + diuron, pyroxasulfone + flumioxazin, and a control without herbicide), and five post-emergence herbicide treatments: control without herbicide, glyphosate at two rates (930 and 1,550 g a.e. ha-1), applied alone or in combination with clethodim. The herbicide sulfentrazone caused persistent phytotoxicity and resulted in the lowest soybean grain yield. The herbicide S-metolachlor was ineffective in controlling weed species, except barnyard grass, even when combined with post-emergence application. The poor control of these weed species does not result in significant interference, causing no significant decreases in grain yield of soybean crops grown in floodplain soils. The use of S-metolachlor, diclosulam, and pyroxasulfone + flumioxazin, combined with post-emergence application of glyphosate (930 g a.e. ha-1), resulted in highly effective control of barnyard grass, inhibiting weed seed production. Only the combination of glyphosate (1,550 g a.e. ha-1) with clethodim can suppress barnyard grass seed production without using pre-emergence herbicides.

Evaluation of row width and nozzle selection on spray coverage and weed control in flooded rice

Abstract Barnyardgrass and other troublesome weeds have become a major problem for producers in a flooded rice system. Cultural control options and more efficient herbicide applications have become a priority to increase efficiency and weed control in rice. This study aimed to determine the effects of row width and nozzle selection on spray coverage and weed control in a flooded rice system. A field experiment was conducted at 7 site-years (Lonoke, AR, in 2021 and 2022; Pine Tree, AR, in 2021 and 2022; Rohwer, AR, in 2022; and Stoneville, MS, in 2021 and 2022) as a randomized complete block split-plot design. Five nozzles (XR, AIXR, TTI, TTI60, and AITTJ60) (subplot factor) were used for herbicide applications, and plots were drill-seeded in four row widths (whole plot factor) (13, 19, 25, and 38 cm). A droplet size experiment was conducted to evaluate the droplet size and velocity of each nozzle type used in the field experiment. Overall, as row width increased, barnyardgrass density increased. The rice grown in a wider width took longer to generate canopy closure, allowing weed escapes in the crop. For example, the 13-cm width had a 12 percentage point canopy coverage increase compared to the 38-cm row width at the preflood timing resulting in a reduction of six barnyardgrass plants per square meter. The smallest droplet size-producing nozzle (XR) provided greater weed control throughout the study but is more prone to drift. The dual-fan nozzles (AITTJ60 and TTI60) had variable weed control impacts, and it was difficult to predict when this might occur; however, they did have increased deposits on water-sensitive cards compared to single-fan counterparts (AIXR and TTI). In conclusion, a narrower row width (e.g., 19-cm or less) and a smaller droplet size producing nozzle (XR) are optimal for barnyardgrass control in a flooded rice system.

Two-Pass Weed Management Programs for Identity-Preserved Soybean

Weed management is a challenge in Identity-Preserved (IP) soybean in Ontario, Canada. Six experiments were established in southwestern Ontario, Canada during 2021 and 2022 to evaluate weed control and soybean yield with preemergence (PRE), early postemergence (EPOST), and PRE followed by (fb) late POST (LPOST) herbicide programs. At 8 weeks after LPOST herbicide applications, S-metolachlor/metribuzin, pyroxasulfone/sulfentrazone, and flumioxazin/metribuzin/imazethapyr applied PRE provided 7, 49, and 99% control of velvetleaf; 65, 98, and 100% control of green pigweed; 7, 8, and 82% control of common ragweed; 25, 68, and 98% control of common lambsquarters; 91, 77, and 89% control of barnyardgrass; and 62, 68, and 93% control of green foxtail, respectively. Imazethapyr + bentazon applied EPOST provided 91% control of velvetleaf; 91% control of green pigweed; 78% control of common ragweed; 95% control of common lambsquarters; 76% control of barnyardgrass; and 79% control of green foxtail. S-metolachlor/metribuzin, pyroxasulfone/sulfentrazone, and flumioxazin/metribuzin/imazethapyr applied PRE fb bentazon + fomesafen + quizalofop applied LPOST provided 61, 86, and 100% control of velvetleaf; 97, 99, and 100% control of green pigweed; 94, 88, and 99% control of common ragweed; 96, 98, and 100% control of common lambsquarters; 97, 95, and 97% control of barnyardgrass; and 97, 96, and 99% control of green foxtail, respectively. There was minimal and transient soybean injury (6% or less) with all PRE or EPOST herbicide treatments, however, S-metolachlor/metribuzin, pyroxasulfone/sulfentrazone, or flumioxazin/metribuzin/imazethapyr applied PRE fb bentazon + fomesafen + quizalofop LPOST caused up to 22% injury in soybean. Weed interference reduced soybean yield 40%. Weed interference with S-metolachlor/metribuzin and pyroxasulfone/sulfentrazone applied PRE reduced soybean yield 25 and 31%, respectively. Reduced weed interference with flumioxazin/metribuzin/imazethapyr applied PRE, imazethapyr + bentazon applied EPOST, and the two-pass programs of a PRE fb LPOST herbicide resulted in soybean yield that was similar to the weed-free control. This study concludes that there are many effective weed management programs in IP soybean; however, the two-pass weed control programs are recommended since they provide good to excellent weed control, minimize soybean yield loss from weed interference, and ensure the use of multiple herbicide modes of action which reduces the selection intensity for the evolution of herbicide-resistant weeds.

Weed control and rice response to microencapsulated acetochlor and a fenclorim seed treatment on a clay soil

AbstractRecent research has demonstrated the ability of a fenclorim seed treatment to reduce rice (Oryza sativa L.) injury to acetochlor. However, all studies were conducted on silt loam soils and have not evaluated rice tolerance or weed control on clay soils. Experiments were initiated in 2021 and 2022 at the Northeast Research and Extension Center near Keiser, AR, to determine rice response and the effectiveness of delayed‐preemergence (DPRE)‐applied microencapsulated (ME) acetochlor (1.1, 1.7, and 2.3 lb ai acre−1) when applied to a clay soil with and without a fenclorim seed treatment at 0 or 2.5 lb ai 1000‐lb−1 of seed. Averaged over the fenclorim seed treatment, acetochlor at 1.1 and 1.7 lb ai acre−1 caused similar injury levels to rice; however, barnyardgrass [Echinochloa crus‐galli (L.) P. Beauv.] control increased at 1.7 lb ai acre−1, eliciting 19% injury to rice and 82% barnyardgrass control at 28 days after emergence (DAE). Palmer amaranth (Amaranthus palmeri S. Watson) control ranged from 82% to 93%. Additionally, fenclorim did not influence barnyardgrass or Palmer amaranth control, but it did reduce rice injury and increase shoot density, plant height, and rough rice grain yield. At 14 and 28 DAE, fenclorim at 2.5 lb ai 1000‐lb−1 of seed (averaged over acetochlor rates) reduced visible rice injury from 61% to 13% and 40% to 8%, respectively. Results from this study indicate ME acetochlor could be successfully applied to rice grown on a clay soil when a fenclorim seed treatment is used, providing producers a new site of action for use in U.S. rice production.

Barnyardgrass (Echinochloa crus-galli) control and rice injury with labeled herbicides following exposure to sub-lethal concentrations of paraquat

Abstract Rice in Mississippi is often in early seedling growth stages when paraquat-based herbicide treatments are commonly applied to corn, cotton, and soybean; therefore, off-target movement onto adjacent rice fields may occur. After an off-target movement event has occurred, weed management in the rice crop is still necessary. Field studies were conducted from 2019 to 2021 in Stoneville, MS, to evaluate rice injury and barnyardgrass control with labeled herbicides after exposure to a sub-lethal paraquat concentration. Labeled herbicide treatments were recommended rates of imazethapyr, quinclorac, propanil, bispyribac-sodium, cyhalopfop, and florpyrauxifen-benzyl applied following rice exposure to a sub-lethal concentration of paraquat. Rice injury was detected 7 and 28 d after treatment (DAT) with injury ≥ 35 and 14%, respectively, following all labeled herbicides. Florpyrauxifen-benzyl and imazethapyr injured rice the greatest 28 DAT. Following paraquat exposure, barnyardgrass control was similar for all labeled herbicide treatments 7, 14, and 28 DAT except with florpyrauxifen-benzyl and no labeled herbicide (paraquat alone) 7 DAT. Across all evaluations, barnyardgrass control was at least 12% greater following paraquat exposure and labeled herbicide treatments than with no paraquat exposure. The current research demonstrates that labeled herbicides applied following exposure to a sub-lethal concentration of paraquat resulted in <36% injury and provided as great as 95% control of barnyardgrass, depending on the herbicide treatment. Therefore, the labeled herbicides choice following rice exposure to a sub-lethal concentration of paraquat should be based on weed spectrum.

Salvage treatments for barnyardgrass (Echinochloa crus-galli) control in rice following simulated failed herbicide application

Abstract Florpyrauxifen-benzyl was commercialized in 2018 to target barnyardgrass and aquatic or broadleaf weeds. Field studies were conducted from 2019 to 2021 in Stoneville, MS, to evaluate barnyardgrass control following a simulated failure of florpyrauxifen-benzyl or other common postemergence rice herbicides. In the first field study, florpyrauxifen-benzyl was applied at 0 and 15 g ai ha–1 to rice at the two- to three-leaf stage to simulate a failed application targeting barnyardgrass. Sequential herbicide treatments included no herbicide and full rates of imazethapyr, quinclorac, bispyribac-Na, and cyhalofop applied 7 or 14 d after florpyrauxifen-benzyl treatment. The second field study was designed to evaluate barnyardgrass control with florpyrauxifen-benzyl following simulated failure of postemergence rice herbicides. Initial herbicide treatments included no herbicide and half rates of imazethapyr, quinclorac, bispyribac-Na, and propanil. Sequential applications at 7 or 14 d after the initial herbicide treatments included florpyrauxifen-benzyl at 0 and 30 g ai ha–1. Results from the first study indicated barnyardgrass control 21 d after final treatment (DAFT) was greater with sequential treatments at 7 compared with 14 d after initial treatment (DA-I) with no initial application of florpyrauxifen-benzyl. Therefore, delaying sequential treatments until 14 d after initial florpyrauxifen-benzyl at 15 g ha–1 allowed barnyardgrass to become too large to control with other rice herbicides. Rough rice yield was reduced in plots where quinclorac application was delayed from 7 to 14 DA-I with no initial application of florpyrauxifen-benzyl. The second study suggested that florpyrauxifen-benzyl application should be delayed 14 d after a herbicide failure. Although no differences in barnyardgrass control 21 DAFT were detected whether florpyrauxifen-benzyl was applied 7 or 14 DA-I of any herbicide utilized, >85% control was only achieved when florpyrauxifen-benzyl application was delayed 14 DA-I. These results demonstrate barnyardgrass control options following simulated failed applications of common rice herbicides.

Evaluation of weed control efficacy and crop safety of the PPO-inhibiting herbicide tiafenacil in California orchard cropping systems

Abstract Tiafenacil is registered in the United States for use in annual crops such as corn and soybean, but not on orchard crops. Field studies were conducted to determine orchard crop safety and efficacy of tiafenacil on important California orchard weeds. To evaluate crop safety, tiafenacil was applied at 74, 148, and 222 g ai ha−1 alone and with 38 g ai ha−1 of tolpyralate three times per year at the base of almond, pistachio, prune, and walnut trees. The first treatment was applied 2 mo after the trees had been transplanted. In all four tree crop experiments, treatments were applied once in May 2020, then three times again during the winter of 2021 and 2022 at 21-d treatment intervals. There were no visual foliar injury symptoms or treatment-related effects on tree trunk diameter change even at the highest tested rate of tiafenacil applied seven times over three growing seasons. In a separate study of weed control, in most instances, tiafenacil applied at 12 g ai ha−1 performed similarly to that of tiafenacil plus glufosinate. Control of glyphosate-resistant hairy fleabane with tiafenacil applied alone at 25 g ai ha−1 was 65% by 14 d after treatment. Tiafenacil applied at 50 g ai ha−1 to hairy fleabane performed similarly to glufosinate plus glyphosate. In a greenhouse study, tiafenacil applied at 12 g ha−1 provided 95% to 100% control of barnyardgrass and junglerice, and there was no significant difference between tiafenacil applied alone or with glufosinate. Saflufenacil applied alone or in a mixture with glufosinate was not as effective as the tiafenacil treatments for grass weed control. Based on experiments conducted over three growing seasons in four tree fruit and tree nut crops, tiafenacil crop safety appeared to be acceptable even at up to 2- or 3-fold the expected use rate.

Flood timing and flood loss impact on effectiveness of florpyrauxifen-benzyl coated on urea in rice

Abstract Florpyrauxifen-benzyl has generated complaints and concerns around rice injury and off-target movement to soybean since its commercial launch in 2018. Developing a precise method for applying florpyrauxifen-benzyl was imperative for its continued use. Experiments were conducted in 2020 and 2021 to evaluate rice weed control as influenced by preflood application interval and flood loss following florpyrauxifen-benzyl at 30 g ai ha−1 applied as a spray or coated on urea. In a preflood application experiment, coating florpyrauxifen-benzyl on urea and applying it the day of flood establishment and 5 and 10 d prior to flooding (DPTF) resulted in lower yellow nutsedge, broadleaf signalgrass, and barnyardgrass control than when the herbicide was spray at 3 and 5 wk after final treatment (WAFT). Coating florpyrauxifen-benzyl onto urea provided only 61% to 63% yellow nutsedge control at 3 and 5 WAFT, which was 35 to 37 percentage points lower than when the spray was applied at 5 or 10 DPTF. Likewise, rice yields following applications of florpyrauxifen-benzyl coated onto urea were 1,200 kg ha−1 less than yields following spray applications. Florpyrauxifen-benzyl coated onto urea and clomazone provided lower levels of weed control than spraying the herbicide alone, suggesting an explanation for the yield losses. The timing of flood loss experiment suggested that when florpyrauxifen-benzyl coated onto urea at 30 g ai ha−1 was applied preflood and flood was relinquished at 2 h, 24 h, and 7 d after flood establishment, hemp sesbania and yellow nutsedge control were not affected. However, loss of floodwater 2 h after flood establishment resulted in lower barnyardgrass control than when the flood was lost 24 h and 7 d after flooding. Generally, the period between a herbicide application and flooding completion should be minimized to aid in weed control. These results indicate the importance of maintaining a flood for weed control and nutrient management.

Effectiveness of preemergence- and postemergence-applied oxyfluorfen in rice compared to current standards

Abstract Control of barnyardgrass is becoming increasingly difficult as plants evolve resistance to herbicides. ROXY oxyfluorfen-resistant rice (ROXY® Rice Production System) has been developed to provide an alternative mode of action for controlling barnyardgrass and other weeds. In 2021 and 2022, field trials were conducted at the Pine Tree Research Station near Colt, AR; the Northeast Research and Extension Center in Keiser, AR; and the University of Arkansas Pine Bluff Small Farm Research Center near Lonoke, AR, to determine the level of weed control and crop tolerance following oxyfluorfen applied preemergence (PRE) or postemergence (POST) relative to herbicides currently labeled for use in rice crops. When applied post-plant PRE on silt loam soil, oxyfluorfen alone at 1,120 and 1,680 g ai ha−1 resulted in barnyardgrass control comparable to that of clomazone applied alone at 336 g ha−1. Still, injury to rice was often greater than with clomazone, ranging from 20% to 45%. On clay soil, oxyfluorfen applied at 1,680 g ha−1 resulted in barnyardgrass control that was comparable to that of clomazone alone in both site-years at 3 wk after emergence but caused up to 18% injury to rice. When oxyfluorfen was applied at 560 to 1,680 g ha−1 at the 2-leaf rice growth stage, barnyardgrass control was ≥85% in three of four site-years 1 wk after treatment. However, injury to rice ranged from 38% to 73% for the rates evaluated. Propanil caused the greatest injury by a herbicide currently labeled for use in rice at 34%. Oxyfluorfen should be used as a post-plant PRE herbicide rather than a POST herbicide due to the injury that occurred after a POST application. The data indicate that if used as a PRE herbicide, oxyfluorfen should be applied at 560 g ha−1 to reduce the injury that occurred on silt loam and clay soils.

Barnyardgrass control in conventional and Clearfield rice grown under intermittent flooding

AbstractIn the mid‐southern United States, rice (Oryza sativa L.) is flooded primarily to suppress weed germination and growth. Two experiments were conducted to determine whether herbicide performance in conventional or Clearfield rice weed control programs was affected by intermittent flooding. The effects of flooding and herbicide program on barnyardgrass [Echinochloa crus‐galli (L.) P. Beauv] control, rice grain yield, and water applied were investigated at the Delta Research and Extension Center in Stoneville, MS, on Sharkey clay (very fine, smectitic, thermic Chromic Epiaquert). For herbicides commonly applied in conventional (clomazone, quinclorac, pendimethalin, thiobencarb, fenoxaprop‐ethyl, cyhalofop‐butyl, and bisypriboac sodium) or Clearfield rice weed control programs (imazethapyr plus bispyribac‐sodium followed by imazethapyr, imazamox or bispyribac‐sodium), intermittent flooding had no adverse effect on barnyardgrass control relative to a continuous flood. Moreover, initiating irrigation when the perched water table drops to 8 inches below the soil surface had no effect on rice grain yield and reduced water applied by 51%. Mid‐southern US rice producers can capture the water‐saving benefits of intermittent flooding while having no adverse effects on herbicide activity or crop productivity in conventional and Clearfield systems.

Effect of Class Act NG Adjuvant on Glyphosate Efficacy in Corn

There is little information on the effect of the co-application of glyphosate with Class Act NG adjuvant on weed control efficacy and corn yield under Ontario environmental conditions. This study consisted of 6 field experiments that were conducted in Ontario during 2021 and 2022 to determine if the addition of Class Act NG (2.5% v/v) to glyphosate at 450, 900 and 1350 g ae ha-1 would improve weed control and result in a concomitant increase in corn yield. The co-application of glyphosate with Class Act NG resulted in no visible corn injury at 1 and 4 weeks after herbicide application (WAA). The addition of Class Act NG to glyphosate at 450 g ae ha-1 improved control of common lambsquarters, velvetleaf, Powell amaranth, common ragweed, and barnyardgrass as much as 20, 14, 9, 8, and 7%, respectively but there was no improvement in control of giant foxtail, or green foxtail and there was no increase in corn yield. The addition of Class Act NG to glyphosate at 900 g ae ha-1 improved common lambsquarters control 6 and 5% at 4 and 8 WAA, respectively and improved barnyardgrass control 4% at 4 WAA. The addition of Class Act NG to glyphosate at 1350 g ae ha-1 provided no improvement in control of velvetleaf, Powell amaranth, common ragweed, common lambsquarters, barnyardgrass, giant foxtail, or green foxtail and there was no increase in corn yield. Based on this data the co-application of glyphosate with Class Act NG results in improved control of some annual broadleaf and grass weeds (common lambsquarters, velvetleaf, Powell amaranth, common ragweed and barnyardgrass) when glyphosate is applied at 450 or 900 g ae ha-1; however, when glyphosate is applied at 1350 g ae ha-1 there was no improvement in weed control. The addition of Class Act NG to glyphosate at 450, 900 and 1350 g ae ha-1 did not result in an increase in corn yield.

Variability to flooding tolerance in barnyardgrass and early flooding benefits on weed management and rice grain yield

Barnyardgrass (Echinochloa crus-galli (L.) Beauv.) is one of the most problematic weed species in paddy fields. The recent large-scale evolution of herbicide resistance in this species requires the adoption of integrated methods of weed control. The present study aimed to determine the interaction of water depth, flooding irrigation onset, and pre-emergent herbicides on the control of barnyardgrass populations and to identify the variability and the putative genes involved in the regulation of flooding tolerance in this species. We identified tolerant, moderately tolerant, and flood-sensitive barnyardgrass populations through water depth-response experiments in a greenhouse. The relative expression of genes related to flooding tolerance were evaluated to confirm the flooding tolerance variability. A field experiment was conducted during the summer seasons of 2020/21 and 2021/22 to assess the interaction of the flooding onset, water depth, and pre-emergent herbicides on populations with different flood tolerances and herbicide resistance mechanisms. Water depths of 7.5 cm and 12.5 cm and plant height were selected for the diagnosis of flood tolerance. After 28 days under flooding, the 7.5 cm depth reduced plant height by an average of 26.82%. Of the 45 populations evaluated, 43 overcame the water depth of 7.5 cm, and four surpassed 12.5 cm. The relative expression of alcohol dehydrogenase 1 (ADH1), alcohol dehydrogenase 2 (ADH2), pyruvate decarboxylase (PDC1), aldehyde dehydrogenase (ALDH), and sucrose synthase 3 (SUS3) was between eight and sixteen times higher for the flood-tolerant population than for the sensitive one. In the field study, the anticipation of flooding to the two-leaves (V2) stage of rice resulted in an increase of up to 55.6% in the control of all populations evaluated compared with conventional irrigation at the four-leaves (V4) stage, including those resistant to herbicides. The grain yield was increased by approximately 11.4% with flooding onset in the V2 stage compared to the V4 stage. Barnyardgrass control and rice grain yield were not affected by water depths of 5 cm or 15 cm. The early flooding, in the V2 stage, increased rice grain yield and favored barnyardgrass control. However, variability in flood tolerance was identified in barnyardgrass populations, which may jeopardize the effect of early flooding for weed control in rice crops. The results we obtained add information on the basic knowledge of flooding tolerance in barnyardgrass and to the integrated weed management for dry direct-seeded rice.

First report on ALS herbicide resistance in barnyardgrass (Echinochloa crus-galli) from rice fields of India

AbstractBispyribac-sodium, a herbicide that inhibits acetolactate synthase (ALS), is frequently used in rice fields in India to control weeds, including the most common noxious weed, barnyardgrass. However, rice growers have recently reported reduced control of barnyardgrass with bispyribac-sodium. Hence, a large-scale survey was carried out to assess bispyribac-sodium resistance in Chhattisgarh and Kerala, two rice-growing states. Open-field pot experiments were conducted for 2 yr to confirm resistance to bispyribac-sodium. Of the 37 biotypes tested, 30% (11) survived the recommended label rate of bispyribac-sodium (25 g ai ha−1). The effective rate of bispyribac-sodium required to achieve 50% control (ED50) of putative resistant biotypes ranged from 18 to 41 g ha−1, whereas it was about 10 g ha−1 for susceptible biotypes. This suggests that putative biotypes were two to four times more resistant to bispyribac-sodium. At 6 d after herbicide application, an in vitro enzyme assay demonstrated higher ALS enzyme activity in putative resistant biotypes (66% to 75%) compared with susceptible biotypes (48% to 52%). This indicates the presence of an insensitive ALS enzyme in those biotypes and a target site mutation as a possible mechanism for resistance. Whole-plant bioassays also suggested that the resistance problem is more widespread in Chhattisgarh than in Kerala. This study confirmed the first case of evolved resistance in barnyardgrass to bispyribac-sodium in rice fields of India.

Quick bioassay test from tillers for detecting ALS herbicide resistance of weedy rice and barnyardgrass

Resistance to acetolactate synthase (ALS) inhibitors have increased recently in South Brazil where the major weeds of flooded rice (barnyardgrass and weedy rice) have evolved resistance to imazapyr+imazapic. The aim of this research was to evaluate a growth medium for tissue regeneration of tillers in barnyardgrass, as well as an agar-based bioassays test (also from tillers) to detect susceptible and resistant biotypes of weedy rice and barnyardgrass to imazapyr+imazapic in vitro. Greenhouse experiments were conducted to detect ALS-resistant (R) and susceptible (S) weedy rice and barnyardgrass biotypes, and bioassays were carried out to evaluate an adequate growth medium for barnyardgrass tiller regeneration and determine the concentration of herbicide to distinguish R and S plants. The culture medium that provided a suitable barnyardgrass growth was MS 50% with the addition of benzylamino-purine. The tissue regeneration in vitro with the growth medium containing imazapyr+imazapic allowed to discriminate between R and S barnyardgrass and weedy rice plants. The concentration required for satisfactory control of susceptible barnyardgrass and weedy rice explants grown in vitro was 0.9 μM and 1.3 μM of imazapyr+imazapic herbicide, respectively. The bioassay in vitro using tiller regeneration provides an opportunity to predict effectively imazapyr+imazapic resistance in barnyardgrass and weedy rice.

Efficacy of Pendimethalin Rates on Barnyard Grass (Echinochloa crus-galli (L.) Beauv) and Their Effect on Photosynthetic Performance in Rice

Pendimethalin herbicide toxicity to rice plants and barnyard grass invasion have increasingly affected the productivity of direct-seeded rice (DSR) in the fields. Whether and how to promote DSR productivity and sustain weed management depend on the appropriate pre-emergence herbicide application rate to minimise its toxicity in the rice ecosystem. Pot experiments were conducted to determine the effects of pendimethalin rates (1.5, 1.75, 2.0 kg a.i. ha−1, two control treatments include the untreated control and the treated control with 1.5 kg a.i. ha−1 S-metolachlor) on barnyard grass (Echinochloa crus-galli (L.) Beaux) and their potential toxicity risk to photosynthetic performances of rice (Topaz and Sen pidao). All the pendimethalin treatments provided excellent control of barnyard grass. Among the treatments, 1.5, 1.75, 2.0 kg a.i. ha−1 pendimethalin and 1.5 kg a.i. ha−1 S-metolachlor (treated control) decreased leaf area of barnyard grass significantly by 38.9, 49.6, 49.6 and 46.2%, respectively, compared with the untreated control at 40 days after sowing (DAS). The above-ground biomass of barnyard grass significantly decreased by 40% (1.48 g plant−1) with 2.0 kg a.i. ha−1 pendimethalin and by 46.2% (1.33 g plant−1) when 1.5 kg a.i. ha−1S-metolachlor was applied at 40 DAS compared with the untreated pots. Higher pendimethalin rates increased toxicity in Topaz and Sen pidao varieties, and 2.0 kg a.i. ha−1 pendimethalin significantly reduced effective quantum yield (light-adapted) of photosystem (PS) II by 18% (0.58) and 19% (0.52), respectively, compared with the untreated control. Application of 2.0 kg a.i. ha−1 pendimethalin rate significantly decreased the maximum quantum yield (dark-adapted) of Sen pidao (0.66) compared with 1.5 kg a.i. ha−1 pendimethalin (0.68) including the untreated control. All pendimethalin treatments suppressed above-ground biomass at 55 DAS, but above-ground biomass of barnyard grass significantly decreased by 59.9% when 2.0 kg a.i. ha−1 pendimethalin was applied compared with the untreated control. Although application of 1.5 kg a.i. ha−1 pendimethalin rates reduced the effective quantum yield (light-adapted) of photosystem II of Sen pidao (0.55) by a small percentage (8%) than Topaz (0.65), it was non-toxic for both varieties compared with 2.0 kg a.i. ha−1 pendimethalin. Therefore, the use of 1.5 kg a.i. ha−1 pendimethalin can be used for effective weed management in the direct seeding of rice at an early growth stage.

Colletotrichum echinochloae: A Potential Bioherbicide Agent for Control of Barnyardgrass (Echinochloa crus-galli (L.) Beauv.).

Barnyardgrass (Echinochloa crus-galli (L.) Beauv.) is one of the most troublesome weeds in transplanted and direct-seeded rice worldwide. To develop a strategy for the biocontrol of barnyardgrass, fungal isolates were recovered from barnyardgrass plants that exhibited signs of necrosis and wilt. An isolate B-48 with a high level of pathogenicity to barnyardgrass was identified after pathogenicity tests. From cultural and DNA sequence data, this strain was identified as Colletotrichum echinochloae. The inoculation of the barnyardgrass plant with C. echinochloae caused a significant reduction in fresh weight. The isolate B-48 was highly pathogenic to barnyardgrass at the three- to four-leaf stages. When inoculated at a concentration of 1 × 107 spores/mL, barnyardgrass could achieve a reduction in fresh weight of more than 50%. This strain was safe for rice and most plant species. The results of this study indicated that this strain could be a potential mycoherbicide for barnyardgrass control in paddy fields in the future.

Response of Soybean (Glycine max (L.) Merr.) and Weed Control with Postemergence Herbicides and Combinations of Cytokinin Mixtures

A field study was conducted in 2015 and 2016 in Stoneville, MS, to evaluate the influence of cytokinin products on soybean injury and weed control when combined with common POST soybean herbicide treatments. Cytokinin treatments included no cytokinin mixture and two formulated cytokinin mixtures (kinetin-1 and kinetin-2) applied at 0.000227 kg ai ha−1. Herbicide treatments were no herbicide, glyphosate at 1.37 kg ae ha−1 alone and in combination with S-metolachlor at 1.42 kg ai ha−1 or fomesafen 0.395 kg ai ha−1. The addition of cytokinin treatments had no impact on soybean injury, plant height, or yield. Glyphosate plus fomesafen provided the greatest level of Palmer amaranth control, between 84 and 67%., 7 days and 28 days after treatment, respectively. Barnyardgrass control with glyphosate plus fomesafen was antagonized by one of two cytokinin products. To prevent possible reductions in herbicide efficacy, tank mixtures with cytokinin products should not be applied to soybean in POST herbicide applications.

Evaluation of rice tolerance and weed control with acetochlor and fenclorim

AbstractMany problematic weeds have evolved resistance to herbicides in mid-southern U.S. rice fields. With the lack of new effective herbicides, rice producers seek alternatives that are currently not labeled for rice production. Inhibitors of very-long chain fatty acid elongase (VLCFA) are currently not labeled for use with U.S. rice crops but are labeled for use in other U.S. row cropping systems and rice production in Asia. Previous research has demonstrated the utility of VLCFA inhibitors for weed control in rice; however, these herbicides induce variable amounts of injury to the crop when applied early in the growing season. Experiments were initiated in 2020 and 2021 at the Rice Research and Extension Center near Stuttgart, AR, to evaluate rice tolerance and weed control with acetochlor and seed treatment with a herbicide safener, fenclorim. Three rates of a microencapsulated formulation of acetochlor (630, 1,260, and 1,890 g ai ha−1), four application timings (preemergence, PRE; delayed-preemergence, DPRE; spiking; and 1-leaf), and without or with the fenclorim seed treatment (2.5 g kg−1 of seed) were used to evaluate rice tolerance, weedy rice control, and barnyardgrass control. Acetochlor applied DPRE at 1,260 g ai ha−1 provided better weedy rice and barnyardgrass control than applications at the 1-leaf stage at the same rate. Acetochlor rates of 1,260 and 1,890 g ai ha−1 reduced barnyardgrass and weedy rice densities by more greater than the 630 g ai ha−1 rate. The fenclorim seed treatment did not influence weedy rice or barnyardgrass control but did reduce injury for DPRE acetochlor applications. Based on these results, acetochlor can be safely applied to rice DPRE (≤19% injury) at 1,260 g ai ha−1 when the seed is treated with fenclorim, leading to ≥88% barnyardgrass and ≥45% weedy rice control 28 d after treatment.