Quinclorac Applications Research Articles

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.

Assessing a programmatic approach for the control of quinclorac‐resistant smooth crabgrass (Digitaria ischaemum) in established bermudagrass turf

AbstractThe auxin‐mimicking herbicide quinclorac controls crabgrass (Digitaria spp.) after emergence in cool‐ and warm‐season turfgrass species. Quinclorac resistance has been confirmed in smooth [Digitaria ischaemum (Schreb.) Muhl.] and large crabgrass [Digitaria sanguinalis (L.) Scop.]. Two Mississippi smooth crabgrass populations have been confirmed as quinclorac‐resistant. Field experiments were conducted to evaluate programmatic approaches to control one of these populations. Treatments included the sequential application of pre‐emergence herbicides on 17 Feb. and 10 Apr. 2020, and 25 Feb. and 6 Apr. 2021, alone or with 0.84 kg quinclorac ha–1 applied postemergence on 10 April 2020 and 6 April 2021, then a second application of quinclorac alone on 18 June 2020 and 16 June 2021. Pre‐emergence treatments included 0.05 kg indaziflam ha–1, 0.84 kg prodiamine ha–1, 0.56 kg dithiopyr ha–1, and 0.47 kg prodiamine ha–1 + 0.21 kg imazaquin ha–1 + 0.73 kg simazine ha–1. Commercial standards applied on 10 Apr. and 18 June 2020, and 6 Apr. and 16 June 2021 included 0.16 kg pinoxaden ha–1 and 2.27 kg monosodium methanearsonate ha–1. Four weeks after the last application, all treatments except quinclorac (2020 and 2021), dithiopyr (2020), and pinoxaden (2020) controlled quinclorac‐resistant smooth crabgrass by >90%. Various standard pre‐emergence herbicides adequately controlled the resistant population. Quinclorac combined with pre‐emergence strategies provided greater control of smooth crabgrass than quinclorac alone. Ongoing research is investigating the mechanism of quinclorac resistance. Future research should screen a wider distribution of populations and investigate cross‐ and multiple resistance.

Field bindweed control with quinclorac in highbush blueberry

AbstractField bindweed is a perennial vining weed with vigorous growth, and is commonly found in highbush blueberry fields of Oregon. It requires and integrated strategy using multiple applications of postemergence herbicides and hand weeding for adequate control. Quinclorac is a herbicide that has been shown to control field bindweed, but no information is available indicating the tolerance of blueberry to quinclorac. The objective of this study was to evaluate the response of blueberry to quinclorac and to evaluate field bindweed control with quinclorac in different mixtures. Three groups of field studies were designed to assess 1) single application control of field bindweed, 2) use of sequential treatments to control field bindweed, and 3) long-term impact of quinclorac on field bindweed. In the single application control studies, a single application of quinclorac at 210 or 420 g ai ha−1 alone or in a mixture with rimsulfuron (35 g ai ha−1) or carfentrazone (35 g ai ha−1), controlled field bindweed by 69% to 76% while reducing its biomass between 22% and 44% compared to the nontreated control (61 g m−2). In a sequential treatment study, a single application of quinclorac (420 g ai ha−1) provided 83% to 100% control of field bindweed, outperforming three sequential applications of carfentrazone. In the long-term study, a single application of quinclorac reduced field bindweed biomass by 50% to 82% in 2019 and 62% to 87% in 2020. These results indicate that quinclorac can be safely applied to highbush blueberry plants. Early spring applications of quinclorac to field bindweed will reduce or eliminate the need for subsequent applications later in the season.

Herbicide tolerance in 11 grass species for minimal‐to‐no‐mow golf course rough

AbstractResearch was conducted to determine the tolerance of 11 grass species used in minimal‐to‐no‐mow turf areas to three postemergence herbicides applied at one‐ and twofold the maximum label rates in 2018 and 2019. Grasses were transplanted into field plots in West Lafayette, IN, in 2018 and 2019, allowed time to establish (∼1−2 mo), and then either treated with one application of quinclorac, sethoxydim, and topramezone at two rates or not treated. All 11 grass species had acceptable tolerance (≤20% injury) to quinclorac applied at 0.845 kg acid equivalent (a.e.) ha–1. Quinclorac at 1.69 kg a.e. ha–1 produced moderate injury (≥21% injury) on only little bluestem [Schizachyrium scoparium (Michx.) Nash.], prairie dropseed [Sporobolus heterolepis (A. Gray) A. Gray], and switchgrass (Panicum virgatum L.). Strong creeping red fescue (Festuca rubra L. ssp. rubra Gaudin), which had ≤5% injury from all three herbicides, exhibited the greatest tolerance among grass species tested. With the exception of strong creeping red fescue, sethoxydim significantly injured all other grass species. Injury from topramezone varied among grass species and herbicide rates. Grasses tolerant (≤20% injury) to topramezone at both rates were big bluestem (Andropogon gerardii Vitman), broomsedge bluestem (Andropogon virginicus L.), indiangrass [Sorghastrum nutants (L.) Nash], strong creeping red fescue, and tall fescue [Festuca arundinacea Schreb.; syn. Schedonorus arundinaceus (Schreb.) Dumort., nom. cons.]. Tolerance among species was variable to quinclorac, sethoxydim, and topramezone, and thus turf managers should first identify desired grass species prior to herbicide application.

Influence of Nitrogen Fertilization on Herbicide Selectivity in Rice

ABSTRACT: Chemical weed control and nitrogen fertilization are common practices in irrigated rice crops. Nitrogen is an essential element for growth and development of plants and may influence herbicide selectivity. In this study, herbicide selectivity was evaluated according to nitrogen application time in irrigated rice crops. The experiment was conducted in the field in a split-plot design with four replications. Treatments were arranged in a factorial scheme: factor A consisted of different nitrogen application times (without nitrogen, all nitrogen applied before flooding, half of the nitrogen rate applied before flooding and the other half after flooding, all nitrogen applied after flooding); factor B consisted of the application of the herbicides quinclorac, bentazon, bispyribac-sodium and carfentrazone-ethyl. Nitrogen application increased plant height and dry matter accumulation in rice plants, while nitrogen application before flooding and split N applications were favorable to the crop. The herbicide bispyribac-sodium causes the greatest injury and the greatest reduction in rice plant height, followed by bentazon and carfentrazone-ethyl, while the lowest injury and the highest grain yield were caused by the application of quinclorac.

Effect of Temperature and Moisture on Quinclorac Soil Half-life and Resulting Native Grass and Forb Establishment

Quinclorac will control leafy spurge and not injure many established native grasses and forbs. Seeding of desirable species is often required to reestablish native vegetation after an invasive weed-management program, but quinclorac residue may inhibit the reestablishment of native species. Greenhouse studies were conducted to estimate quinclorac dissipation rates in Northern Great Plains soils and the effect of residue on establishment of some native grass and broadleaf plants. Quinclorac 50% dissipation time (DT50) ranged from > 21 to 112 d in four soils from the Northern Great Plains. The quinclorac DT50 was dependent on several factors including soil type, moisture content, temperature, and especially organic matter (OM). Across four different soil textures, quinclorac dissipation generally increased as soil moisture content increased, but moisture had less of an impact in low OM soils. Quinclorac dissipation also increased as temperature increased in the four soils. The most rapid dissipation occurred in soils with higher OM (> 6%), with an average DT50 of < 38 d, at 45% moisture content, held at 16 C. Wild bergamot, purple coneflower, blanketflower, and stiff goldenrod seedling growth were all reduced by quinclorac residue at 6 μg kg−1, the lowest concentration evaluated in the study. The native grass species big bluestem, intermediate wheatgrass, and switchgrass generally were tolerant of quinclorac, but green needlegrass was sensitive, and seedling growth declined as quinclorac residue increased from 6 to 375 μg kg−1. Based on a quinclorac application of 840 kg ha−1 and 150 frost-free d, seeding of sensitive forbs and grasses should be delayed at least 12 mo after herbicide application.

Salicylic acid mediates antioxidant defense system and ABA pathway related gene expression in Oryza sativa against quinclorac toxicity

The auxin herbicide quinclorac is widely used for controlling weeds in transplanted and direct-seeded rice fields. However, its phytotoxic responses on rice are still unknown. Therefore, in the present investigation we studied the effects of different concentrations (0, 0.1 and 0.5g/L) of quinclorac herbicide on the physiological and biochemical changes of two rice cultivars (XS 134 and ZJ 88) and further analyzed the ameliorating role of salicylic acid (SA) on quinclorac toxicity in rice plants. The results revealed that exogenous application of SA significantly increased plant biomass and total chlorophyll contents in herbicide stressed plants. The lipid peroxidation and ROS (H2O2, O2−., −OH) production were significantly increased in roots and leaves of both rice cultivars under quinclorac stress, demonstrating an oxidative burst in rice plants. Whereas, application of SA significantly lowered ROS contents under quinclorac stress. Further, exogenous SA treatment significantly modulated antioxidant enzymes and enhanced GSH concentration in stress plants. Anatomical observations of leaf and root revealed that herbicide affected internal structures, while SA played a vital role in protection from toxic effects. Expression analysis of stress hormone ABA genes (OsABA8oxs, OsNCEDs) revealed that quinclorac application enhanced stress condition in cultivar ZJ 88, while SA treatment downregulated ABA genes more in cultivar XS 134, which correlated with the enhanced tolerance to quinclorac induced oxidative stress in this cultivar. The present study delineated that SA played a critical role under quinclorac stress in both rice cultivars by regulating antioxidant defense system, reducing ROS formation and preventing the degradation of internal cell organelles.

Switchgrass Establishment Influenced by Cover Crop, Tillage Systems, and Weed Control

Successful establishment of switchgrass (Panicum virgatum L.) is often challenging. The objective of this study was to improve switchgrass stand establishment through integrated management practices that included cover crops, tillage systems and herbicide application. The study was conducted at the University of Massachusetts Agricultural Experiment Station in Deerfield during the growing seasons of 2012 and 2013. A split split-plot design with three replications was used in both years. The main plots consisted of three cover crop treatments (fallow, oat [Avena sativa L.], and rye [Secale cereale L.]). The sub-plots were two seeding methods (no-till drill, and cultipacker seeder [Brillion]). The sub sub-plots were herbicide treatments that consisted (1) pre-emergence (PRE) application of atrazine (A) and quinclorac (Q) and (2) a Broad Spectrum application of PRE A + Q that was supplemented with post-emergence (POST) application of 2,4-D and dicamba. The no-till seeding method in both years resulted in higher stand density and biomass. Weed control was improved with the Broad Spectrum herbicide (0.90 Mg ha−1) compared with A + Q treatment (1.3 Mg ha−1). No-till seeding produced considerably higher tiller numbers (190 tiller m−2) than that of cultipacker seeder which in turn resulted in significant weed suppression. In general, when planted after rye, switchgrass produced fewer tillers than after oat or fallow. No-till seeding into oat mulch with the application of Broad Spectrum herbicides resulted in highest switchgrass yield (2,098 kg ha−1) in the establishment year.

Effect of Postflood Quinclorac Applications on Commercial Rice Cultivars

Rice cultivar, growth stage at application, or both may influence rice tolerance to quinclorac. Field studies were conducted to compare the response of five rice cultivars ‘Bowman’, ‘Cheniere’, ‘CL161’, ‘Cocodrie’, and ‘XL723’ to postflood quinclorac applications. Quinclorac at 0.56 kg ai ha−1was applied 2 and 4 wk after flood (WAF). Pooled across quinclorac application timings, no differences in maturity were detected among the cultivars in 2008, but maturity of Cheniere and XL723 were delayed compared with CL161 and Cocodrie in 2007. Maturity of Cheniere and XL723 was delayed in 2007 compared with 2008. Pooled over cultivar, maturity was similar for 2 and 4 WAF applications in 2007 but was delayed for 2 WAF treatments in 2008. Regardless of year, postflood quinclorac applications reduced rough rice yield of all cultivars except Bowman. Cheniere and XL723 had lower rough rice yields compared with other cultivars in 2007; however, in 2008, rough rice yields of Cheniere, CL161, Cocodrie, and XL723 were similar, but still lower, than that of Bowman. Pooled over cultivar, postflood quinclorac reduced rough rice yields more when applied 4 WAF than at 2 WAF during both years. Our results demonstrate that Cheniere and XL723 are less tolerant than Bowman is to postflood quinclorac applications and that all evaluated cultivars are more susceptible to quinclorac applied at later developmental stages. Consequently, if circumstances necessitate a postflood quinclorac application, the herbicide should be applied no later than panicle initiation and should not be applied to Cheniere or XL723.

Selective Postemergence Herbicide Control of Torpedograss in Centipedegrass

Torpedograss infestation in centipedegrass has reduced centipedegrass quality in home lawns along the Gulf Coast. This study was conducted to evaluate three selective postemergence herbicides. Field trials were conducted at two sites in Louisiana to evaluate quinclorac, sethoxydim, and clethodim applied once or sequentially every 4 wk for selective torpedograss control in centipedegrass turf. Herbicides were applied to mixed stands of torpedograss/centipedegrass at two locations in Louisiana and evaluated for changes in torpedograss coverage and centipedegrass injury every 2 wk for 16 wk. All herbicides controlled torpedograss more with each sequential application. Sethoxydim and clethodim applied three times reduced torpedograss cover 84 and 87%, respectively, and more than quinclorac 12 wk after initial treatment (WAIT). Increasing clethodim or sethoxydim rates did not improve torpedograss control. Torpedograss regrowth occurred within weeks after final herbicide applications regardless of herbicide. Only multiple clethodim applied at twice manufacturer's labeled rate or quinclorac applications resulted in commercially unacceptable (> 25%) injury to centipedegrass. Multiple sethoxydim or clethodim applications at 0.32 kg ha−1or 0.30 kg ha−1every 4 wk reduced torpedograss competitiveness in centipedegrass; however, multiple applications for more than 1 yr might be necessary to achieve torpedograss control.

Herbicides for Establishing Switchgrass in the Central and Northern Great Plains

Weed interference limits switchgrass (Panicum virgatum L.) establishment from seed. Our objectives were to determine the effect of selected post-plant, preemergence herbicides on stand establishment and subsequent biomass yields of adapted upland switchgrass cultivars grown in three environments in the Central and Northern Great Plains. A separate experiment was conducted in eastern Nebraska to determine if there were any differences among switchgrass ecotypes for herbicide tolerance to the optimal herbicide combination. Herbicides applied immediately after planting were different concentrations of atrazine [Aatrex 4L®; 6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine], quinclorac (Paramount®; 3,7-Dichloro-8-quinolinecarboxylic acid), atrazine+quinclorac, imazapic {Plateau®; 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-methyl-3-pyridinecarboxylic acid}, and quinclorac+imazapic. Herbicide efficacy was determined by measuring stand frequency of occurrence and biomass yield the year after establishment. The application of quinclorac plus atrazine resulted in acceptable stands and high biomass yields. Imazapic often reduced switchgrass stands in comparison to the nontreated control and is not recommended for switchgrass establishment. In the multi-state trials, the herbicide by cultivar interaction was not significant for stands or biomass yields, indicating that the effects of herbicides on switchgrass stands and biomass yields were consistent over the upland cultivars used in the trials. No differences were detected among switchgrass lowland and upland ecotypes for tolerance to atrazine and quinclorac. Quinclorac, which provides effective control of grassy weeds, and herbicides such as atrazine which provide good broadleaf weed control are an excellent herbicide combination for establishing switchgrass for biomass production in the Great Plains and the Midwest.

Timing of Oxadiazon and Quinclorac Application on Newly Sprigged Turfgrass Species

Tolerance of sprigged ‘Tifsport’ and ‘Tifdwarf’ bermudagrass, ‘Meyer’ zoysiagrass, and ‘Salam’ seashore paspalum to oxadiazon (2,240 g/ha) or quinclorac (840 g/ha) applied 1 wk before sprigging (WBS), at sprigging (AS), 2 wk after sprigging (WAS), and 4 WAS was investigated in the field. Weed control was also evaluated. For both herbicides only the AS application timing injured the turfgrass greater than 22%, and injury for the other application timings ranged from 9 to 19% 5 WAS. When evaluated 8 WAS turfgrass injury following the AS application timing remained at 19%, and injury for all other timings was 8% or less. Eight WAS the 1 WBS, AS, 2 WAS, and 4 WAS application timings achieved 89, 79, 94, and 99% plot coverage, respectively, when averaged over all turfgrass species/cultivars and herbicides. By 13 WAS, all species/cultivars achieved at least 90% plot coverage. Presprigging applications of oxadiazon provided 98 to 100% goosegrass and old world diamond-flower control. Quinclorac applied AS provided greater than 70% control of these weeds. Results indicate that oxadiazon and quinclorac applied AS will cause unacceptable turfgrass injury. If goosegrass and/or old world diamond-flower are problematic, oxadiazon is a feasible choice for control of these weeds, but quinclorac is not.

Efficacy of Two Dithiopyr Formulations for Control of Smooth Crabgrass [Digitaria ischaemum (Schreb) Schreb. ex Muhl.] at Various Stages of Growth

Although dithiopyr has been used for smooth crabgrass [Digitaria ischaemum (Schreb) Schreb. ex Muhl.] control for many years, data describing the efficacy of a new, water-based formulation of dithiopyr for smooth crabgrass control are limited. Research was conducted in Knoxville, TN, and Griffin, GA, evaluating water-based and wettable powder dithiopyr formulations at 0.56 and 0.43 kg·ha−1 for smooth crabgrass control when applied at the pre-emergence (PRE), one- to two-leaf (1LF), one- to two-tiller (1TL), and greater than three-tiller (3TL) stages of growth. These treatments were compared with quinclorac (0.84 kg·ha−1) applied at the same POST timings (i.e., 1LF, 1TL, and 3TL). When applied PRE, all dithiopyr treatments provided greater than 85% smooth crabgrass control at the end of the trial in both locations. At the 1LF stage, both rates and formulations of dithiopyr provided greater than 93% smooth crabgrass control at 4 weeks after application and greater than 77% at the end of the trial. Applied at the 1TL stage in Tennessee, no differences in smooth crabgrass control were detected between quinclorac and any dithiopyr treatment at the end of the trial; when applied in Georgia at the 1TL stage, quinclorac provided greater smooth crabgrass control at the end of the trial than either rate or formulation of dithiopyr. Although no differences were detected between any dithiopyr treatment and quinclorac applied at the 3TL stage in Tennessee, smooth crabgrass control at the end of the trial measured less than 70% for all treatments. At the end of the trial in Georgia, smooth crabgrass control with quinclorac (91%) was greater than both formulations of dithiopyr. These findings suggest that both the wettable powder and water-based formulations of dithiopyr can be used to effectively control smooth crabgrass at the PRE and 1LF stages of growth, but quinclorac should be selected over dithiopyr for control of tillering smooth crabgrass plants. Turfgrass managers should implement smooth crabgrass control measures at PRE and 1LF timings, because erratic responses can be observed with both dithiopyr and quinclorac applications to smooth crabgrass after tillering. Chemical names used: dithiopyr (S,S-dimethyl 2-(difluoromethyl)-4-(2-methylpropyl)-6-(trifluoromethyl)-3,5-pyridinedicarbothioate); quinclorac (3,7-dichloro-8-quinolinecarboxylic acid).

Herbicide Options for Rice Cutgrass (Leersia oryzoides) Control

Rice cutgrass is encroaching into rice fields from ditch banks and canals, especially into continuous rice fields where tillage is limited in the Mississippi Delta region of Arkansas. Experiments were conducted to evaluate the effectiveness of various herbicides applied alone on rice cutgrass and to determine if the effectiveness of bispyribac on rice cutgrass is influenced by number of applications, adjuvant type, and adjuvant rate. Glyphosate, glufosinate, and clethodim were the most effective herbicides when applied alone; however, none of these are labeled for over-the-top application in rice. Of those herbicides that can be applied over the top of rice, imazethapyr and bispyribac were the most effective, providing 52 to 62% rice cutgrass control, albeit imazethapyr can be used only in imidazolinone-resistant rice. The addition of an adjuvant to bispyribac improved rice cutgrass control, and sequential bispyribac applications were generally superior to a single application. Methylated seed oil/organosilicone/urea ammonium nitrate adjuvant increased rice cutgrass control with bispyribac, especially when bispyribac was applied as a single application. A single application of imazethapyr, bispyribac, halosulfuron, penoxsulam, clomazone, thiobencarb, cyhalofop, propanil, quinclorac, and fenoxaprop provided less-than-acceptable control, which partially explains the difficulty that growers are experiencing in controlling rice cutgrass, especially in continuous rice production.

History and Management of Herbicide-resistant Barnyardgrass (Echinochloa Crus-galli) in Arkansas Rice

Arkansas has been the leading state in rice production in the United States for many years. Barnyardgrass is the dominant weed in Arkansas rice. Propanil was the first highly effective herbicide for weed control in rice and has been used in Arkansas since 1959 as the primary herbicide for rice weed control. By 1989, its continual use led to the development of propanil-resistant barnyardgrass, which had spread to 16 of the 38 rice-producing counties in Arkansas by 1992. Arkansas rice growers are dependent on herbicides for the control of weeds in this drill-seeded crop. The residual herbicides thiobencarb, molinate, and pendimethalin mixed with propanil applied early postemergence improved control of propanilresistant barnyardgrass. But it was quinclorac, introduced in 1992, that became the real replacement treatment for propanil-resistant barnyardgrass. Then in 1999, a barnyardgrass biotype with resistance to both quinclorac and propanil was confirmed in Craighead County, Arkansas. Additionally, problems with quinclorac drift to other crops, especially tomato, led to restrictions on application of quinclorac in Arkansas by 1994. Fortunately, alternative herbicides for barnyardgrass control were developed, and clomazone was introduced in 2000. Clomazone is currently the standard herbicide for annual grasses in rice, including barnyardgrass. Herbicides recently developed for rice allow a broad range of options for a resistance management program, based on rotational and sequential herbicide applications. These include fenoxaprop and cyhalofop (both acetyl-CoA carboxylase [ACCase] inhibitors), bispyribac and penoxsulam (acetolactate synthase [ALS] inhibitors), and imazethapyr and imazamox (also ALS inhibitors for imidazolinone-resistant rice). From a global standpoint, there is considerable evidence that barnyardgrass has the propensity to develop resistance to most of these herbicide groups. Therefore, efforts to manage and monitor for herbicide resistance in this species need to be diligently continued. Research on nonchemical options is in progress utilizing weed-suppressive rice breeding lines to control barnyardgrass. Nomenclature: 2,6-bis[(4,6-dimethoxy-2-pyrimidinyl)oxy]benzoic acid, proposed common name bispyribac-sodium; clomazone; cyhalofop; fenoxaprop; imazamox; imazethapyr; molinate; pendimethalin; {2-(2,2-difluoroethoxy)-6(trifluoromethyl-N-(5,8-dimethoxy[1,2,4]triazolo[1,5-c]pyrimidin-2-yl))benzenesulfonamide}, proposed common name penoxsulam; propanil; quinclorac; thiobencarb; barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG; rice, Oryza sativa L.; tomato, Solanum lycopersicum L.

Effects of Multiple Applications of Simulated Quinclorac Drift Rates on Tomato

Quinclorac drift has been speculated as the cause of injury to tomato crops throughout northeast Arkansas. In this study, we set out to determine whether tomato plant injury and yield reduction were correlated with simulated quinclorac drift. Experiments were carried out at Fayetteville, AR, in 1999 and 2000. Maximum plant injury (visual ratings) was about 20% when plants were treated with one, two, or three quinclorac applications (weekly intervals beginning at first flower) at 0.42 g ai ha−1(0.001 times the normal use rate to simulate drift). Maximum plant injury ranged from 48 to 68% with quinclorac simulated drift treatment of 42 g ha−1. Overall, increasing quinclorac rate and number of applications increased tomato injury. In both years, tomato plant fresh-weight accumulation was not influenced by one, two, or three applications of quinclorac at 0.42 g ha−1compared with the untreated control. In 1999, increasing the rate of quinclorac from 0.42 to 4.2 g ha−1reduced plant fresh-weight accumulation. In 2000, there was no significant difference in plant fresh weight when plants were treated with quinclorac at 2.1 to 4.2 g ha−1. Evaluation of the herbicide rate effect indicated that quinclorac at 0.42 g ha−1did not reduce tomato fruit yield (total weight of edible fruit) compared with the untreated control, but yield decreased as rate increased above 0.42 g ha−1. Increasing the number of applications generally decreased tomato yield, and overall as maximum visual plant injury increased, tomato yield reduction ALSo increased linearly. We conclude that quinclorac at simulated drift rates can adversely affect tomato plant growth and yield.

Physiological and Biochemical Characterization of Quinclorac Resistance in a False Cleavers (Galium spurium L.) Biotype

The physiological and biochemical basis for quinclorac resistance in a false cleavers (Galium spurium L.) biotype was investigated. There was no difference between herbicide resistant (R) and susceptible (S) false cleavers biotypes in response to 2,4-D, clopyralid, glyphosate, glufosinate-ammonium, or bentazon. On the basis of GR(50) (growth reduction of 50%) or LD(50) (lethal dose to 50% of tested plants) values, the R biotype was highly resistant to the acetolactate synthase (ALS) inhibitor, thifensulfuron-methyl (GR(50) resistance ratio R/S = 57), and quinolinecarboxylic acids (quinclorac R/S = 46), resistant to MCPA (R/S = 12), and moderately resistant to the auxinic herbicides picloram (R/S = 3), dicamba (R/S = 3), fluroxypyr (R/S = 3), and triclopyr (R/S = 2). The mechanism of quinclorac resistance was not due to differences in [(14)C]quinclorac absorption, translocation, root exudation, or metabolism. Seventy-two hours after root application of quinclorac, ethylene increased ca. 3-fold in S but not R plants when compared to controls, while ABA increased ca. 14-fold in S as opposed to ca. 3-fold in R plants suggesting an alteration in the auxin signal transduction pathway, or altered target site causes resistance in false cleavers. The R false cleavers biotype may be an excellent model system to further examine the auxin signal transduction pathway and the mechanism of quinclorac and auxinic herbicide action.

Use of Quinclorac for Large Crabgrass (Digitaria sanguinalis) Control in Newly Summer-Seeded Creeping Bentgrass (Agrostis stolonifera)

Field trials were conducted in 2000 and 2001 in New Jersey to evaluate quinclorac and siduron for large crabgrass control in summer-seeded creeping bentgrass (‘L-93’). Bentgrass was surface seeded on June 30 and June 26 in 2000 and 2001, respectively. Treatments consisted of preemergence (PRE) applications of siduron at 3.4, 5.0, and 6.7 kg ai/ha and PRE and postemergence (POST) applications of quinclorac at 0.4, 0.6, 0.8, and 1.7 kg ai/ha. POST applications were timed to a crabgrass growth stage of three leaves to one tiller. All POST quinclorac applications included methylated seed oil at 1% (v/v). Percent crabgrass cover in untreated plots at 30 d after planting (DAP) averaged 10 and 50% in 2000 and 2001, respectively. All PRE treatments, with the exception of quinclorac applied at 0.4 kg/ha in 2001, reduced crabgrass cover by 80% or more at 30 DAP. Crabgrass control decreased in late August when siduron and quinclorac were applied at the lower rates in 2001. PRE quinclorac applications at the rate of 0.6 kg/ha or higher in 2000 or 1.7 kg/ha in 2001 caused significant thinning of the bentgrass stand at 30 DAP. All POST quinclorac treatments provided excellent crabgrass control in 2000, but the 0.8-kg/ha or higher rate was required to reduce crabgrass infestation levels by at least 80% in 2001. All POST quinclorac applications caused significant chlorosis to the creeping bentgrass in both years. However, significant thinning of the bentgrass stand was not evident, with the exception of 1.7 kg/ha, in 2001. These studies suggest that PRE applications of siduron should be used for the highest level of creeping bentgrass safety in summer restoration projects. The use of quinclorac should be limited to POST applications to control escaped crabgrass once the newly emerging creeping bentgrass has become well established.

Smooth Crabgrass Control in Perennial Ryegrass and Creeping Bentgrass Tolerance to Quinclorac

Smooth crabgrass [Digitaria ischaemum (Schreber) Schreber ex Muhlenb.] is an invasive weed of cool-season turfgrasses. Previous research has demonstrated that quinclorac is an effective postemergence herbicide for crabgrass control, but performance has been erratic in some regions. Furthermore, quinclorac may elicit objectionable levels of discoloration in creeping bentgrass (Agrostis stolonifera L.). The objectives of this 3-year field study were to determine optimum rates and timings of quinclorac applications that provide consistent levels of effective crabgrass control and to assess creeping bentgrass quality responses to quinclorac. To evaluate crabgrass control, quinclorac was applied in early-, mid- and late-postemergence timings at various rates to a perennial ryegrass (Lolium perenne L.) turf. Similar treatments were applied to creeping bentgrass to determine if application timing and rate influenced the level and duration of discoloration. Quinclorac was applied alone or was tank-mixed with either urea (N at 6.1 kg·ha-1) or chelated iron (Fe)+nitrogen (N) (FeSO4 at 1.1 kg·ha-1+N at 2.2 kg·ha-1) to determine if they would mask discoloration. Crabgrass control generally was more effective in the early- and midpostemergence application timings. A single application of quinclorac (0.84 kg·ha-1) was effective where crabgrass levels were moderate, but sequential (i.e. multiple) applications were required where crabgrass levels were severe. The most consistent level of crabgrass control where weed pressure was severe occurred with three, sequential quinclorac (0.37 or 0.42 kg·ha-1) applications. Creeping bentgrass exhibited 2 to 11 weeks of unacceptable discoloration in response to sequential quinclorac applications. Chelated Fe+N was more effective than urea in masking discoloration. In general, chelated Fe+N tank-mixed with quinclorac masked discoloration and turf had quality equivalent to untreated bentgrass on most, but not all rating dates. Chemical names used: 3,7,-dichloro-8-quinolinecarboxylic acid (quinclorac).

Tolerance to Quinclorac by Seedling Creeping Bentgrass

Annual grassy weeds often inhibit establishment of spring-seeded creeping bentgrass (Agrostis palustris Huds.) on golf courses. The objective of this experiment was to evaluate the safety of the annual grass herbicide quinclorac in spring-seeded creeping bentgrass in varying climatic regions of the United States. Experiments were initiated in Indiana, Iowa, and North Carolina in Spring 2000. Treatments included siduron at 6.72 kg·ha-1 a.i. applied immediately prior to planting (PRE), and quinclorac at 0.84 kg·ha-1 a.i. applied 7 days before seeding (DBS), PRE, and 14 or 28 days after emergence (DAE). Herbicides were applied to three creeping bentgrass cultivars at each location. Siduron reduced establishment of `Providence', `L93', and `Putter' creeping bentgrass in Indiana. Quinclorac applied PRE, 14 DAE, and 28 DAE caused short-term phytotoxicity, primarily in `Providence' in Indiana. Quinclorac applications did not significantly affect cover of `Providence', `L93', or `Putter' in Indiana or `L93', `Pennlinks', or `Penncross' in Iowa. All applications of quinclorac reduced cover of `L93', `Pennlinks', and `Penncross' in North Carolina. Though quinclorac applications resulted in no long-term damage when applied to creeping bentgrass seedlings in Indiana or Iowa, results from North Carolina indicate that caution should be exercised when using quinclorac on seedlings of creeping bentgrass. Chemical names used: 3,7-dichloro-8-quinolinecarboxylic acid (quinclorac); 1-(2-methylcyclohexyl)-3-phenylurea (siduron).