Commercialization of florpyrauxifen-benzyl as Loyant® in 2018 as a synthetic auxin herbicide in rice was followed by soybean injury due to off-target movement of spray applications in the mid-southern United States. Concerns surrounding off-target movement led to the exploration of an alternative application method to help alleviate the issue. Field experiments were conducted in 2020 and 2021 to explore the likelihood of a reduction in soybean injury following applications of florpyrauxifen-benzyl coated on urea in narrow- and wide-row soybean systems and to determine the likelihood of volatilization from this novel application method. Florpyrauxifen-benzyl spray-applied at 0.18 g ai ha−1 caused greater than 60% injury, whereas coating the herbicide on urea at 5.63 g ai ha−1 never exceeded 30% injury in narrow-row soybean. Similarly, florpyrauxifen-benzyl spray-applied at 0.18 g ai ha−1 caused greater than 50% injury, whereas coating the herbicide on urea at 5.63 g ai ha−1 never exceeded 30% injury in wide-row soybean. As soybean injury increased, relative yield decreased in both narrow- and wide-row soybean. Spray-applied florpyrauxifen-benzyl decreased relative soybean groundcover, yield components, and soybean survival rate as the herbicide rate increased, whereas coating the herbicide on urea resulted in little to no decrease in both narrow- and wide-row soybean assessments. No negative impacts on relative yield and yield components of soybean from florpyrauxifen-benzyl coated on urea indicates that even though visible injury may persist, there is a low likelihood of any yield losses associated with the herbicide exposure using this application method. Additionally, coating the florpyrauxifen-benzyl on urea did not increase the likelihood of volatilization under any of the evaluated soil moisture conditions. Overall, applying florpyrauxifen-benzyl coated on urea is likely to be a safer application method and can reduce soybean injury compared to spray-applying the herbicide when favorable off-target movement conditions exist.

Complaints regarding the sensitivity of rice to florpyrauxifen-benzyl and off-target movement of the herbicide occurred following its commercial launch in 2018 in the midsouthern United States. These two concerns encouraged the exploration of an alternative application method for florpyrauxifen-benzyl in rice. A field study was conducted in 2020 and 2021 to determine if coating florpyrauxifen-benzyl on urea would reduce negative impacts of the herbicide to rice. Five commercial rice lines were evaluated: ‘Diamond’, ‘Titan’, ‘RT7321 FP’, ‘RT7521 FP’, and ‘XP753’. Florpyrauxifen-benzyl coated on urea at a 2× rate (60 g ai ha–1) reduced rice injury in one of five commercial rice lines in 2020 and four of five commercial rice lines in 2021, compared to spray applications at the same rate. In 2020, ‘RT7521 FP’ exhibited a 17-percentage point injury reduction when coating florpyrauxifen-benzyl on urea at a 2× rate vs. the same rate sprayed. In 2021, rice injury was reduced by 26, 10, and 27 percentage points in the commercial rice lines ‘Diamond’, ‘Titan’, and ‘XP753’, respectively, following coated urea vs. spray applications at 4 wk after treatment (WAT). ‘XP753’ exhibited reduced injury (15 percentage points) by coating florpyrauxifen-benzyl at a 1× rate (30 g ai ha–1) 4 WAT in 2021, and another, ‘Diamond’, had comparable groundcover to nontreated plots when florpyrauxifen-benzyl was coated on urea at a 1× rate rather than the reductions observed from the spray application at a 2× rate. Yield differences were a function of urea rate rather than application method, where in six out of ten instances greater rough rice grain yield occurred at the higher rate. Findings from this experiment indicate that coating florpyrauxifen-benzyl on urea can reduce the amount of injury observed, especially in areas of overlap where you would have a 2× rate.

Tiafenacil is a new nonselective protoporphyrinogen IX oxidase–inhibiting herbicide with both grass and broadleaf activity labeled for preplant application to corn, cotton, soybean, and wheat. Early season rice emergence and growth often coincide in the mid-southern United States with applications of preplant herbicides to cotton and soybean, thereby increasing the opportunity for off-target herbicide movement from adjacent fields. Field studies were conducted to identify any deleterious effects of reduced rates of tiafenacil (12.5% to 0.4% of the lowest labeled application rate of 24.64 g ai ha−1) applied to 1- or 3-leaf rice. Visual injury 1 wk after treatment (WAT) for the 1- and 3-leaf growth stages ranged from 50% to 7% and 20% to 2%, respectively, whereas at 2 WAT these respective ranges were 13% to 2%, and no injury was observed. Tiafenacil applied at those rates had no negative season-long effect because observed early season injury was not manifested as a reduction in rice height 2 WAT or rough rice yield. Application of tiafenacil to crops directly adjacent to rice in its early vegetative stages of growth should be avoided because visual injury will occur. When off-target movement does occur, however, the affected rice should be expected to fully recover with no effect on growth or yield, assuming adequate growing conditions and agronomic/pest management are provided.

Bearded sprangletop is a problematic native grass weed in California’s rice fields. The widespread and extensive use of acetyl-CoA carboxylase (ACCase)–inhibiting herbicides, such as cyhalofop-p-butyl (cyhalofop), has led to speculation that biotypes of bearded sprangletop have developed herbicide resistance to ACCase. The aim of this study was to evaluate suspected resistant bearded sprangletop biotypes, R1, R2, R3, and the susceptible biotype, S1, in terms of their levels of resistance to three ACCase-inhibiting herbicides and to characterize the molecular mechanisms of resistance. Dose–response experiments suggested that the biotype R1, R2, and R3 had high-level resistance to cyhalofop and to quizalofop-p-ethyl (quizalofop), but not clethodim. The study determined that the resistance to ACCase inhibitors was a target-site mechanism resulting from nucleotide substitution. The carboxyl transferase (CT) domain of the ACCase gene’s sequence analysis revealed the substitutions Trp-2027-Cys for R1 and R2 biotypes and Ile-2041-Asn for the R3 biotype. This study revealed the presence of target-site resistance to cyhalofop and quizalofop in at least two mutation points in representative biotypes of bearded sprangletop in California. This research highlights the significance of careful herbicide selection due to weed species responding quite rapidly to selection pressure, so as to aid in managing bearded sprangletop in rice fields.

Two separate field studies were conducted at two locations near Crowley, Louisiana, to evaluate early season applications of florpyrauxifen and a prepackaged mixture of halosulfuron plus prosulfuron in water-seeded rice production. In each study, florpyrauxifen and halosulfuron plus prosulfuron were applied at two rates and either applied to the soil surface 48 h before the seeding flooding and seeding, directly onto the pregerminated seed 24 h following seeding and immediately after removal of the seeding flood (SEED), and at pegging. Data suggest that both florpyrauxifen and halosulfuron plus prosulfuron have a role to play in water-seeded rice production. Crop injury of 19% was observed from applications of florpyrauxifen applied directly to pregerminated SEED. Additionally, 28% crop injury was observed when halosulfuron plus prosulfuron was applied directly to SEED. Due to crop injury observations, both herbicides should be avoided when the pregerminated seed is exposed to the soil surface after removing the seeding flood. These data suggest that florpyrauxifen may be a better option for postemergence application, whereas halosulfuron plus prosulfuron may be a better preemergence option in water-seeded rice production. Overall, the findings show that both herbicide technologies will provide adequate early-season weed control in water-seeded rice production.

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.

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.

In Iran, monochoria is a noxious weed in fields of transplanted rice. Two field experiments were conducted to assess the efficacy of soil-applied and foliar-applied herbicides to control monochoria in transplanted rice. Prepackaged herbicides (triafamone plus ethoxysulfuron applied at 40 g ai ha−1, pyrazosulfuron-ethyl plus pretilachlor applied at 382.5 g ai ha−1, and pendimethalin plus clomazone applied at 1,200 g ai ha−1) reduced monochoria biomass by 100%, 100%, and 14%, respectively; and a single application of flucetosulfuron at 30 g ai ha−1, pendimethalin at 990 g ai ha−1, thiobencarb at 2,750 g ai ha−1, and pretilachlor at 1,000 g ai ha−1 reduced monochoria biomass by 100%, 99%, 75%, and 56%, respectively, compared with a nontreated control. Tank-mixed bensulfuron-methyl at 45 g ai ha−1 applied with pretilachlor, thiobencarb, or pendimethalin provided 100% control of monochoria. Rice height, and straw and grain yield were greater after herbicide treatments than those of the nontreated and hand-weeded controls, indicating the advantages of chemical control of monochoria over manual weeding. Full-season monochoria interference reduced rice grain yield by 32%. In the second study, the herbicides triafamone plus ethoxysulfuron, flucetosulfuron, 2,4-D at 1,080 g ai ha−1, dicamba plus 2,4-D at 928 g ai ha−1, bispyribac-sodium at 31.25 g ai ha−1, bentazon plus MCPA at 1,150 g ai ha−1, pyribenzoxim at 30 g ai ha−1, and propanil at 5,400 g ai ha−1 applied to foliage at 4- to 5-leaf seedlings of monochoria provided ≥97% control and prevented 100% of its regrowth, with the exception of propanil. This study shows that monochoria control can be achieved by using a variety of residual and foliar-applied herbicides with different mechanisms of action.

Bispyribac-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.

“Weedy” red rice is a problematic weed with phenotypic similarities to cultivated rice. Limited herbicide availability has driven a need for nonchemical control options for managing this pest. One preplanting strategy that is being explored is the stale seedbed methodology, which aims to maximize soil seedbank withdrawals via germination. This technique is adapted in rice by flooding a field, waiting for germination and emergence of weed seedlings, and completing the method with a mechanical or chemical control application. Optimization of this process is dependent on maximizing weed seed germination, which is primarily influenced by both temperature and moisture availability. Germinability across a range of these factors is not well understood in California red rice. Thus, this study aimed to determine germinability of California red rice accessions under various temperature and water potential treatments. Previously described red rice accessions 1, 2, 3, and 5, along with ‘M206’, a common California rice cultivar, were exposed to temperatures from 10 to 40 C in 5 C increments in combination with water potentials of 0, −0.2, −0.4, or −0.8 MPa until either germination or weed seed decay occurred. Statistical analysis indicated a three-way interaction between accession, temperature, and water potential. Germination reached 95% or greater when seeds were exposed to temperatures from 20 to 35 C in combination with 0 or −0.2 MPa. Germination was lowest when seeds were water stressed (−0.8 MPa) and when temperatures were colder than 20 C or warmer than 35 C. The ‘M206’ cultivar was utilized for comparison and demonstrated cold tolerance by germinating at 10 C, whereas weedy accessions 1, 2, and 3 did not. When temperatures were at or above 15 C, however, ‘M206’ germinated less often compared with all weedy accessions. Historical preplant temperatures in this region align with those required for weedy rice germination. Thus, the stale seedbed methodology is a viable strategy in years when ample floodwater is available.

Fall panicum is a problematic weed in cropping systems including rice in southern Florida. There is limited information on growth and reproductive ability of fall panicum in water-stressed environments. The objective of this study was to determine the effect of 12.5%, 25%, 50%, 75%, and 100% pot soil water content (SWC) levels on fall panicum growth and panicle branch production under greenhouse conditions. Fall panicum height, number of leaves, and tillers decreased over time as SWC decreased. Fall panicum height decreased by 65% and 50% at 12.5% and 25% SWC, respectively, relative to height achieved at 100% SWC. Plants at 50% to 100% SWC were able to achieve 50% tiller production within 31 to 43 d compared with 28 d at 25% SWC. The 50% tiller production was not reached at 12.5% SWC during the duration of the study. Fall panicum shoot and root biomass, total leaf area, and number of panicle branches per plant at 56 d after SWC treatment initiation decreased as SWC decreased. Fall panicum biomass decreased 83% to 85% and 66% to 68% at 12.5% and 25% SWC, respectively, relative to 100% SWC. Leaf area declined 79% and 65% at 12.5% and 25% SWC levels, respectively, compared to the 100% SWC. Fall panicum was able to produce panicles at all SWC levels, although the plant produced significantly fewer panicle branches as SWC decreased. Plants at 12.5% and 25% SWC produced 82% and 59% fewer panicle branches, respectively, compared with plants at 100% SWC. This study shows that SWC influences the growth and reproductive capacity of fall panicum. Although fall panicum did not reach its full growth potential at low SWC levels, it was able to survive and develop panicles, showing its ability to adapt and reproduce under dry conditions.

Developing an effective weed management strategy is crucial to sustainable rice production in Nigeria. Rainfed lowland ecology contributes significantly to the volume of rice cultivated in terms of yield and land acreage. Nevertheless, increased weed infestation remains one of the major production constraints. This review highlights the strength and weaknesses of weed management practices in rainfed lowland ecology and research gaps, and examines the potential for developing a sustainable weed management strategy for lowland rice. In this review, a rainfed lowland situation is described (where water is limited) to engage flooding as a potential weed control option, due to the undulating land terrains. Effective weed management begins with creating a weed-free environment at the critical crop growth stages, such that broadcasted or transplanted rice seedlings can efficiently use water, nutrients, and light. Sustainable weed management practices in Nigerian lowland ecology would therefore imply that farmers begin to incorporate crop rotation to suppress problem weeds in continuous rice cropping systems; adopt conventional or minimum tillage to enhance herbicide efficacy and early establishment of rice; adopt weed-competitive and high-yielding cultivars; and practice appropriate spacing, seeding rate, and seeding methods that can support easy adoption of mechanical weeders and optimum plant population to suppress weed pressure at a later growth stage. This is feasible where farmers are supported with infrastructure, farm machinery, and other necessary inputs. Future research should engage lowland rice farmers in specific agroecological zones.

Palmer amaranth is a common weed on levees in rice fields but has become increasingly problematic with the adoption of furrow-irrigated rice and lack of an established flood. Florpyrauxifen-benzyl previously has been found effective for controlling Palmer amaranth in rice, but the efficacy of low rates of florpyrauxifen-benzyl and the effect of Palmer amaranth size on controlling it is unknown. The objective of this research was to determine the level of Palmer amaranth control expected with single and sequential applications of florpyrauxifen-benzyl at varying weed heights. The first study was conducted near Marianna, AR, in 2019 and 2020, to determine the effect of florpyrauxifen-benzyl rate on control of <10 cm (labeled size) and 28- to 32-cm-tall (larger-than-labeled size) Palmer amaranth. The second experiment was conducted in 2020 at two locations in Arkansas to compare single applications of florpyrauxifen-benzyl at low rates to sequential applications at the same rates with a 14-d interval on 20- and 40-cm-tall Palmer amaranth. Results revealed that florpyrauxifen-benzyl at 15 g ae ha−1 was as effective as 30 g ae ha−1 in controlling <10-cm-tall Palmer amaranth (92% and 95% mortality in 2019). Sequential applications of florpyrauxifen-benzyl at 8 g ae ha−1 were as effective as single or sequential applications at 30 g ae ha−1. However, no rate of florpyrauxifen-benzyl applied to 20- or 40-cm-tall Palmer amaranth was sufficient to provide season-long control of the weed, with the escaping female plants producing as many as 6,120 seed per plant following a single application.

Water seeding is a common cropping strategy in mechanized rice systems. Water seeding of rice can suppress grass weeds, but it can also encourage aquatic weeds and grass ecotypes that escape deep floodwater. In addition, water seeding prevents many cultural methods of weed control and limits available herbicides. Selection pressure from a limited palette of herbicides has resulted in widespread resistance in rice grown in California. This study examined a novel combination of drill seeding and a stale seedbed (“stale-drill”) as a means of using a nonselective herbicide to manage weeds before rice emergence. In 2016 and 2017, rice cultivar ‘M-206’ was drilled at a rate of 120 kg ha−1 to 1.3-cm, 2.5-cm, and 5.1-cm depths. Planting rice deeper than 1.3 cm delayed emergence by 3 to 4 d. A postplant-burndown (PPB) treatment of glyphosate at 870 g ha−1 was applied just prior to rice emergence. Treatment delays had mixed effects on weed control. PPB treatment was more effective at controlling Echinochloa spp. in 2017, reducing density by 30%, 48%, and 73% at 1.3-cm, 2.5-cm, and 5.1-cm seeding depths, respectively. The greatest overall weed control either year was found with applications of glyphosate + pendimethalin followed by penoxsulam + cyhalofop at 1.3-cm planting depth. Rice stand and yield components were more strongly affected by planting depth in 2017 than in 2016, possibly owing to cool weather immediately after seeding. Yields in 2017 were reduced in deeper plantings by up to 72%. Therefore, if the stale-drill method is implemented with higher-vigor cultivars or higher seeding rates, we see potential in this method as a useful tool for reducing herbicide-resistant weeds in rice fields.

One of the main limiting factors for high yields of flooded rice (Oryza sativa L.) is the presence of weeds, especially herbicide-resistant weeds. The aim of this study was to evaluate the association of weed management practices adopted by flooded rice farmers in the state of Rio Grande do Sul (RS), Brazil, with grain yield. For this purpose, 324 interview surveys were administered to farmers who supplied information about the history of weed management and yields. The answers to the survey indicated that weedy rice (Oryza sativa L.) and Echinochloa spp. were the most important weeds that occurred in flooded rice areas in RS. Advanced growth stage of weeds and inadequate environmental conditions such as air temperature and relative humidity were listed as the main reasons for low weed control efficacy. Farmers achieved greater rice yields when they adopted rice–soybean [Glycine max (L.) Merr.] (9,140 kg ha−1 average yield) and herbicide site of action rotations (8,801 kg ha−1 average yield) along with tank mixes (8,580 kg ha−1 average yield) as specific management practices for resistant weed control. The use of glyphosate with residual herbicides in a tank mix in the rice spiking stage is the main factor related to greater yields. The postemergence applications and their relationship to delaying of flooding in rice is a factor that reduces rice yield when no spiking glyphosate application was made. Identification of the most important weeds in terms of occurrence and knowledge of the main agronomic practices adopted by farmers are essential so that recommendations for integrated management practices can be adopted in an increasingly accurate and sustainable manner in flooded rice areas in southern Brazil.

A field study was conducted in 2017 and 2018 at the Louisiana State University Agricultural Center H. Rouse Caffey Rice Research Station near Crowley, LA, to evaluate the impact of reduced rates of halosulfuron on quizalofop activity in Louisiana rice production. Halosulfuron and a prepackaged mixture of halosulfuron plus thifensulfuron were evaluated at 0, 17, 35, or 53 g ai ha−1 and 34 or 53 g ai ha−1, respectively, in a mixture with quizalofop at 120 g ai ha−1. Control of barnyardgrass, red rice, and two non-acetyl-CoA carboxylase resistant rice lines, CL-111 and CLXL-745, were recorded at 14 and 28 d after treatment (DAT). The red rice, CL-111, and CLXL-745 represented a weedy rice population. Across all species evaluated at 14 DAT, all mixtures containing halosulfuron and halosulfuron plus thifensulfuron resulted in antagonism with an observed control of 79% to 90%, compared with an expected control of 96% to 99%. At 28 DAT, all mixtures containing halosulfuron resulted in neutral interactions for barnyardgrass control. Quizalofop mixed with halosulfuron plus thifensulfuron at the lower rate of 34 g ha−1 was able to overcome the antagonism compared with the higher rate of 53 g ha−1 for barnyardgrass control at 28 DAT. Both the high and the low rate of halosulfuron plus thifensulfuron resulted in antagonistic interaction for red rice, CL-111, and CLXL-745 control at 28 DAT. This research suggests that mixing quizalofop with halosulfuron plus thifensulfuron should be avoided, especially at the higher rate of 53 g ha−1.

Differential tolerance may be observed among rice cultivars with desiccant exposure events during rice reproduction and ripening. Five field studies were established at the Mississippi State University Delta Research and Extension Center in Stoneville, MS, to determine the effects of exposure to sublethal concentrations of common desiccants across multiple rice cultivars. Rice cultivars in the study were ‘CLXL745’, ‘XL753’, ‘CL163’, ‘Rex’, and ‘Jupiter’. Desiccant treatments included no desiccant, paraquat, or glyphosate and were applied at the 50% heading growth stage respective to cultivar. Differential injury estimates among cultivars and desiccant treatments was observed when glyphosate or paraquat was applied at 50% heading. Injury from glyphosate at 50% heading was nondetectable across all cultivars. However, injury following paraquat applications was >7% across all rating intervals and cultivars. Hybrid cultivars exhibited less injury with paraquat applications than the inbred cultivars in the study. Rice following exposure to glyphosate or paraquat at 50% heading growth stage produced rough rice grain yield decreases ranging from 0% to 20% and 9% to 21%, respectively. Rough rice grain yield decreases were observed across all cultivars following paraquat exposure, and all inbred cultivars following glyphosate exposure. Across desiccant treatment, head rice yield was reduced in three of five cultivars in the study. When pooled across cultivar, paraquat applications cause a head rice yield reduction of 10%, whereas rice yield following glyphosate application remained >95%. Although differential tolerance among cultivars to paraquat or glyphosate exposure was observed, impacts on grain quality coupled with yield reductions suggests extreme rice sensitivity to exposure to sublethal concentrations of these desiccants at the 50% heading growth stage.

A paper-based survey was conducted from 2015 to 2017 among stakeholders of the Texas rice industry on current weed management challenges and factors influencing management decisions. A total of 108 survey questionnaires were completed by stakeholders at the rice Cooperative Extension meetings conducted in the rice-growing counties of Texas. In addition, late-season field surveys were conducted prior to harvest in 2015 and 2016 across the rice-growing counties to understand dominant weed escapes occurring in rice fields. Results from the questionnaire survey revealed that rice–fallow–rice was the most common rotation practiced in Texas rice production. Echinochloa spp., Leptochloa spp., and Cyperus spp. were the top three problematic weed issues faced by the respondents. Among the Leptochloa species, Nealley’s sprangletop, a relatively new species in rice fields, was indicated as an emerging concern. Clomazone was the most frequently used PRE herbicide, whereas quinclorac, propanil, imazethapyr, and cyhalofop were the popular POST herbicides. Most respondents (72%) made weed-control decisions on the basis of economic thresholds, whereas 63% made decisions on the basis of weed problems from previous years. Most respondents (88%) expressed moderate to high concern for herbicide-resistant weeds in their operations. Strategies to manage herbicide-resistant weeds and economical weed management practices were among the top suggested research needs. The field survey revealed that jungle rice, Nealley’s sprangletop, and hemp sesbania were the top three late-season weed escapes in rice production in Texas, with frequencies of occurrence of 28%, 19%, and 13%, respectively. Furthermore, average field area infested by a species was the greatest for jungle rice (13%), followed by hemp sesbania (11%) and weedy rice (11%). Findings from the stakeholder and field surveys help direct future research and outreach efforts for sustainable weed management in Texas rice.

Florpyrauxifen-benzyl and quizalofop were available for POST applications in 2018; however, little is known about the response of acetyl-CoA carboxylase (ACCase)–resistant rice cultivars and advanced lines to POST herbicides. A field study was conducted in 2017 and 2018 at Stoneville, MS, to characterize the response of ACCase-resistant rice cultivars and advanced lines to POST applications of florpyrauxifen-benzyl. The imidazolinone-resistant (IR) rice cultivars ‘CL163’ and ‘CLXL 745’, and ACCase-resistant rice cultivars ‘PVL01’, ‘PVL013’, ‘PVL024-B’, ‘PVL038’, ‘PVL080’, and ‘PVL081’were treated with florpyrauxifen-benzyl at 0 (nontreated control for each cultivar) and 58 g ai ha–1 at the four-leaf to one-tiller (LPOST) growth stage. At 14 d after treatment (DAT), PVL01 was injured 5% to 6% greater than CLXL 745, PVL013, and PVL081; however, injury was ≤10% at that evaluation for all cultivars. Similarly, injury was ≤13% for all cultivars 28 DAT. Mature heights were reduced for all cultivars except PVL013 and PVL081. Rough rice yield was ≥100% of the control for all cultivars except PVL081, PVL013, and CL163. Results suggest that florpyrauxifen-benzyl can safely be applied POST to rice cultivars grown in Mississippi as well as ACCase-resistant cultivars that are currently under development.

In glyphosate-resistant (GR) cropping systems, paraquat applied in mixtures with residual herbicides prior to crop emergence offers an alternative herbicide mode of action (MOA) to aid in GR weed management. Rice is sensitive to off-target herbicide movement; however, severity of injury can vary with herbicide, rate, and formulation. Therefore, research was conducted from 2015 to 2017 in Stoneville, MS, to characterize rice response to a sublethal concentration of paraquat applied at 84 g ai ha–1 in combination with common residual herbicides. Paraquat plus metribuzin injured rice 68% to 69% 14 and 28 d after treatment (DAT), which was 10% to 13% greater than injury following paraquat alone or paraquat plus fomesafen. Pooled across metribuzin and fomesafen treatments, paraquat reduced rough rice yields 23%. Paraquat plus 10 different residual herbicides injured rice ≥51% 28 DAT and reduced rough rice yields ≥21%. These studies indicate a severe negative impact on rice growth and development following exposure to a sublethal concentration of paraquat alone or in mixture with common residual herbicides. Therefore, applications of paraquat plus residual herbicides to fields in proximity to rice should be avoided if conditions are conducive for off-target movement.