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Topramezone and carfentrazone + 2,4-D + mecoprop-p + dicamba (SpeedZone®) are herbicides labeled for POST goosegrass (Eleusine indica L. Gaertn.) control in hybrid bermudagrass (Cynodon dactylon × C. transvaalensis Burtt Davy). Field research was conducted in Knoxville, TN, during 2019 and 2020 to evaluate goosegrass control and hybrid bermudagrass tolerance to these herbicides applied alone and in mixture. Treatments included topramezone (12.2 g ha–1), SpeedZone® [carfentrazone (33.6 g ha–1) + 2,4-D (1,029 g ha–1) + mecoprop-p (322 g ha–1) + dicamba (91 g ha–1)] and SpeedZone® + topramezone at 12.2, 6.1, 3.6, or 2.4 g ha–1. A nontreated control was included for comparison. Hybrid bermudagrass tolerance was assessed on four cultivars (‘Northbridge’, ‘Tifway’, ‘Tahoma 31’, and ‘TifTuf’) via visual ratings of turfgrass injury and assessments of normalized difference vegetation index (NDVI). At the termination of the experiment, SpeedZone® alone and in mixture with topramezone controlled goosegrass better than or equal to topramezone alone. Mixtures of SpeedZone® + topramezone reduced injury on all cultivars compared to topramezone alone, particularly when mixtures delivered ≤6.1 g ha–1 topramezone. Injury subsided on all cultivars by 28 d after treatment regardless of herbicide. Findings suggest that SpeedZone® can be mixed with topramezone at the rates tested herein to minimize hybrid bermudagrass injury from topramezone applications for goosegrass control.
Continued reliance on chemical methods for controlling annual bluegrass has resulted in many populations evolving resistance to PRE and POST herbicides, particularly in warm-season turfgrass species such as zoysiagrass. Soil seedbank management is critically important when managing herbicide-resistant weeds. Fraise mowing (also spelled fraze, frase, and fraize) is a new turfgrass cultivation practice designed to remove aboveground biomass while allowing turf to regrow vegetatively. We hypothesized that this process would remove annual bluegrass seed and therefore be a mechanical means of controlling annual bluegrass in turfgrass. Zoysiagrass field plots were fraise-mowed in June 2015 only, June 2016 only, June 2015 and June 2016, or left untreated. The fraise mower was configured to remove the uppermost 25 mm of plot surface (i.e., 15-mm verdure and 10-mm soil). Annual bluegrass infestation was quantified in April following fraise mowing via grid count. Soil cores (10.8 cm diameter) were extracted from each plot after grid count data were collected to assess effects of fraise mowing on the soil seedbank. Moreover, replicated subsamples (7.6 L) of debris generated during fraise mowing were collected to better understand weed seed content removed during the fraise mowing process. Fraise mowing in June offered a slight reduction (24%) in annual bluegrass cover the following April. Whereas 28% of the seed in fraise-mowing debris consisted of annual bluegrass, there was no difference in the quantity of annual bluegrass seed remaining in the soil seedbank among fraise-mowed and non–fraise-mowed plots. Although fraise mowing may help to temporarily reduce existing annual bluegrass infestations via mechanical removal, the frequency and depth we studied did not effectively reduce the seedbank. Fraise mowing is a useful tool for providing mechanical suppression of annual bluegrass but it is not a replacement for properly timed herbicide applications.
Prodiamine is a dinitroaniline herbicide labeled for PRE control of goosegrass in warm- and cool-season turfgrass. In 2013, several golf course roughs in Maryville, TN reported poor goosegrass control (< 20%) following prodiamine treatment at 1,120 g ai ha-1. We harvested suspected prodiamine-resistant (PR) and prodiamine-susceptible (S) goosegrass phenotypes from the field and exposed them to a range of increasing prodiamine concentrations in hydroponic culture. Exposure to prodiamine at 0.001 mM reduced root growth of the S phenotype to 11% of the non-treated check. By comparison, exposure to 0.001 mM prodiamine had minimal effect on the PR phenotype, as root growth was 94% of the non-treated check. Molecular analyses revealed that PR plants contained a threonine (Thr) to isoleucine (Ile) substitution at position 239 on the α-tubulin 1 (TUA1) protein. The substitution, found in all PR plants, is the mechanism of prodiamine resistance in this phenotype. In field studies, topramezone controlled PR goosegrass 72% to 89% by 50 d after treatment (DAT) compared to only 22% to 23% for foramsulfuron. Topramezone treatment injured bermudagrass 34% to 60% from 7 to 14 DAT; however, injury was≤6% 28 DAT and 0% by the end of the study. Our results indicate that POST applications of topramezone can control dinitroaniline-resistant goosegrass. In addition, we established an easy-to-use genotyping assay to quickly screen goosegrass phenotypes for a target-site mutation (Thr-239-Ile) on TUA1 associated with resistance to dinitroaniline herbicides such as prodiamine. Future research should work to expand this assay for use with other weed species and herbicidal modes of action.
Turfgrass managers currently have few readily available means of evaluating herbicide resistance in annual bluegrass during the growing season. Research was conducted to determine if agar-based diagnostic tests developed for agronomic weeds could be used to reliably confirm herbicide resistance in annual bluegrass harvested from golf course turf. Annual bluegrass phenotypes with target-site resistance to acetolactate synthase (ALS; R3, R7), enolpyruvylshikimate-3-phosphate synthase (EPSPS; R5), and photosystem II (PSII; R3, R4) inhibiting herbicides were included in experiments along with an herbicidal susceptible phenotype (S). Single tiller plants were washed free of soil and transplanted into autoclavable polycarbonate plant culture boxes filled with plant tissue culture agar amended with a murashigee-skoog medium and trifloxysulfuron (6.25, 12.5, 25, 50, 75, 100, or 150 μM), glyphosate (0, 6, 12, 25, 50, 100, 200, or 400 μM), or simazine (0, 6, 12, 25, 50, 100, 200, or 400 μM). Mortality in agar was assessed 7 to 10 days after treatment (depending on herbicide) and compared to responses observed after treating individual plants of each phenotype with trifloxysulfuron (28 g ai ha-1), glyphosate (1120 g ae ha-1), or simazine (1120 g ai ha-1) in an enclosed spray chamber. Fisher’s exact test (α = 0.05) determined that mortality in agar with 12.5 μM trifloxysulfuron and 100 μM glyphosate was not significantly different than treating whole plants via traditional spray application. Mortality with all concentrations of simazine in agar was significantly different than that observed after treating resistant and susceptible phenotypes via traditional spray application. Our findings indicate that an agar-based diagnostic assay can be used to detect annual bluegrass resistance to ALS- or EPSPS-inhibiting herbicides in less than 10 days; however, additional research is needed to refine this assay for use with PSII-inhibiting herbicides.
Methiozolin is an isoxazoline herbicide being investigated for selective POST annual bluegrass control in managed turfgrass. Research was conducted to evaluate methiozolin efficacy for controlling two annual bluegrass phenotypes with target-site resistance to photosystem II (PSII) or enolpyruvylshikimate-3-phosphate synthase (EPSPS)-inhibiting herbicides (i.e., glyphosate), as well as phenotypes with multiple resistance to microtubule and EPSPS or PSII and acetolactate synthase (ALS)-inhibiting herbicides. All resistant phenotypes were established in glasshouse culture along with a known herbicide-susceptible control and treated with methiozolin at 0, 125, 250, 500, 1000, 2000, 4000, or 8000 g ai ha−1. Methiozolin effectively controlled annual bluegrass with target-site resistance to inhibitors of EPSPS, PSII, as well as multiple resistance to EPSPS and microtubule inhibitors. Methiozolin rates required to reduce aboveground biomass of these resistant phenotypes 50% (GR50 values) were not significantly different from the susceptible control, ranging from 159 to 421 g ha−1. A phenotype with target-site resistance to PSII and ALS inhibitors was less sensitive to methiozolin (GR50=862 g ha−1) than a susceptible phenotype (GR50=423 g ha−1). Our findings indicate that methiozolin is an effective option for controlling select annual bluegrass phenotypes with target-site resistance to several herbicides.
2,4-dimethylamine salt (2,4-D) is a selective broadleaf herbicide commonly applied to turfgrass systems, including athletic fields, which can dislodge from treated vegetation. Building on previous research confirming 2,4-D dislodgeability is affected by management inputs, field research was initiated in 2014 and 2015 in North Carolina and Tennessee to quantify the effects of sprayer setup on dislodgeable 2,4-D foliar residue from hybrid bermudagrass, which is the most common athletic field playing surface in subtropical and tropical climates. More specifically, research evaluated dislodgeable 2,4-D foliar residue following spray applications (2.1 kg ae ha−1) at varying carrier volumes (187, 374, or 748 L ha−1) and nozzles delivering varying droplet sizes (fine=extended range [XR], coarse=drift guard, or extra coarse=air induction extended range [AIXR]). Overall, data suggest minimal 2,4-D dislodge occurs via soccer ball roll (3.6 m) outside the day of application; however, increasing carrier volume and droplet size can further decrease dislodgeable 2,4-D foliar residue. At 2 d after treatment (DAT), 3.87% of applied 2,4-D dislodged when applied at 187 L ha−1 compared to 2.05% at 748 L ha−1. Pooled over data from 1 to 6 DAT, 1.59% of applied 2,4-D dislodged following XR nozzle application compared to 1.13% with AIXR nozzle. While these are small numerical differences, dislodgeable residue was measured via one soccer ball roll, which is a repeated process within the sport and the additive effect of sprayer setup treatments can be employed by turfgrass managers to reduce potential human 2,4-D human exposure.
The herbicide pinoxaden is a phenylpyrazoline inhibitor of acetyl coenzyme A carboxylase. Research was conducted to determine the effects of pinoxaden (90 g ai ha−1) alone and in combination with herbicide safeners on creeping bentgrass injury as well as perennial ryegrass and roughstalk bluegrass control. Greenhouse experiments determined that herbicide safeners cloquintocet-mexyl, fenchlorazole-ethyl, and mefenpyr-diethyl were more effective in reducing creeping bentgrass injury from pinoxaden than benoxacor, isoxadifen-ethyl, and naphthalic-anhydride. Other experiments determined that creeping bentgrass injury from pinoxaden decreased as rates (0, 23, 45, 68, 90, 225, or 450 g ha−1) of cloquintocet-mexyl, fenchlorazole-ethyl, and mefenpyr-diethyl increased. On the basis of creeping bentgrass responses to various safener rates, safeners were applied at 68 and 450 g ha−1 in additional experiments to evaluate their effects on pinoxaden (90 g ha−1) injury to creeping bentgrass and efficacy against perennial ryegrass and roughstalk bluegrass. In these experiments, safeners mefenpyr-diethyl and cloquintocet-mexyl reduced pinoxaden-induced creeping bentgrass injury (from 25 to ≤ 5%) more than fenchlorazole-ethyl at 2 wk after treatment. Safeners reduced pinoxaden efficacy against roughstalk bluegrass. Perennial ryegrass was controlled > 80% by pinoxaden and herbicide safeners did not reduce control. Field experiments should evaluate pinoxaden in combination with cloquintocet-mexyl and mefenpyr-diethyl to optimize safener : herbicide ratios and rates for creeping bentgrass safety as well as perennial ryegrass and roughtstalk bluegrass control in different climates and seasons.
Poor annual bluegrass control was reported in golf course roughs following treatment with prodiamine (1120 gaiha−1) and glyphosate (840 gaeha−1) during hybrid bermudagrass dormancy. Research was conducted to determine if this annual bluegrass phenotype was resistant to both prodiamine and glyphosate and to determine the efficacy of herbicide mixtures for controlling this phenotype in the field. In PRE or POST dose-response experiments, 9 to 31 times more prodiamine or glyphosate was needed to control (or reduce dry biomass of) this resistant phenotype by 50% compared to an herbicide-susceptible phenotype. Moreover, glyphosate-susceptible plants accumulated 50% more shikimic acid (898 mgkg−1) 6 d after treatment than those resistant to glyphosate (394 mgkg−1). October (fall) applications of herbicide mixtures containing trifloxysulfuron, simazine, S-metolachlor, or mesotrione controlled this resistant annual bluegrass phenotype 84 to 98% in April (spring), with no differences detected among treatments. Our findings document the second instance of annual bluegrass evolving multiple resistance in a managed turfgrass system. However, several herbicide mixtures can be used to effectively manage this resistant phenotype.
Ground ivy and khakiweed are troublesome broadleaf weeds of warm-season turfgrass. Field studies were conducted in Tennessee (TN) and Texas (TX) from 2008 to 2010 to evaluate the efficacy of sulfentrazone plus metsulfuron and carfentrazone plus metsulfuron tank mixtures compared with metsulfuron alone for control of ground ivy and khakiweed. In TN, sulfentrazone plus metsulfuron and carfentrazone plus metsulfuron provided accelerated control of ground ivy compared with metsulfuron alone. Over a 2-yr period, ground ivy control with metsulfuron at 10, 21, and 42 g ai ha−1 ranged from 0 to 5% 7 d after treatment (DAT) and 12 to 60% 14 DAT. Ground ivy control with mixtures of sulfentrazone plus metsulfuron ranged from 40 to 72% 7 DAT and 87 to 100% 14 DAT. Similarly, carfentrazone plus metsulfuron controlled ground ivy 5 to 32% 7 DAT and 23 to 93% 14 DAT. In TX, carfentrazone plus metsulfuron and sulfentrazone plus metsulfuron controlled khakiweed greater than metsulfuron alone 7 and 14 DAT as well. Few differences in ground ivy and khakiweed control were detected 56 DAT because metsulfuron applied alone at 21 g ai ha−1 controlled both weeds > 77%, similar to each mixture. These data indicate that when applied in mixtures, sulfentrazone and carfentrazone accelerate ground ivy and khakiweed control with metsulfuron but do not affect long-term efficacy.
Flucarbazone controls certain grassy weeds in wheat and may have potential for controlling perennial ryegrass in tall fescue turf. The objective of these experiments was to investigate perennial ryegrass and tall fescue tolerance to flucarbazone at two application timings. In field experiments, flucarbazone applications in May were more injurious to both species than in February and March. Single applications of flucarbazone from 30 to 60 g ai ha−1 in May injured both species 35 to 50% and sequential treatments increased injury approximately twofold. Two applications of flucarbazone at 60 g ha−1 in May injured both grasses > 90%, similar to sequential applications of trifloxysulfuron at 29 g ai ha−1. In growth chamber experiments, injury from flucarbazone on both grasses increased as temperature increased from 10 to 30 C. Flucarbazone reduced total shoot biomass of both grasses at all temperatures after 4 wk. Overall, perennial ryegrass and tall fescue are tolerant to flucarbazone at moderate temperatures (10 to 20 C). However, injury increased substantially under warmer conditions (30 C), suggesting flucarbazone could control perennial ryegrass and tall fescue during late spring and early summer.
Common bermudagrass is a problematic weed within tall fescue turfgrass. Field research was conducted from 2010 to 2012 in Knoxville, TN, evaluating the efficacy of sequential applications of topramezone (12.5 and 25 g ha−1), triclopyr (1,120 g ha−1), and mixtures of topramezone + triclopyr for bermudagrass control in tall fescue turf. Sequential applications of fenoxaprop + triclopyr (100 + 1,120 g ha−1) were included for comparison. Three applications of each treatment were applied at 21-d intervals during July, August, and September of 2010 and 2011. Plots were stripped to receive tall fescue interseeding at 0 or 490 kg ha−1 during September 2010 and 2011. Bermudagrass control with topramezone + triclopyr mixtures was greater than topramezone or triclopyr applied alone 14 wk after initial treatment (WAIT) each year. In the second year of this study, topramezone + triclopyr mixtures controlled bermudagrass 27 to 50% compared to 27% for fenoxaprop + triclopyr by 52 WAIT. However, bermudagrass control with topramezone + triclopyr mixtures increased to 88 to 92% by 52 WAIT when accompanied with tall fescue interseeding at 490 kg ha−1. Future research should evaluate effects of interseeding on the efficacy of different herbicides for weed control in cool- and warm-season turf.
Fenoxaprop effectively controls crabgrass in tall fescue turf, but antagonism with growth-regulating herbicides reduces potential to apply fenoxaprop in combination with many herbicides registered for broadleaf weed control. Aminocyclopyrachlor is a new broadleaf weed control herbicide that has not been evaluated in combination with fenoxaprop. Field experiments were conducted in Georgia, New Jersey, and Tennessee to investigate tank mixtures of fenoxaprop with aminocyclopyrachlor for smooth crabgrass and white clover control. Fenoxaprop alone exhibited substantial activity on smooth crabgrass but control was greater with fenoxaprop + aminocyclopyrachlor treatments. By 4 and 6 wk after treatment (WAT), approximately 22 and 44% less fenoxaprop was required to achieve 80% smooth crabgrass control when the herbicide was tank-mixed with aminocyclopyrachlor at 52.5 and 79 g ai ha−1, respectively. Fenoxaprop did not reduce white clover control with aminocyclopyrachlor because 97% control was achieved by 4 WAT for all aminocyclopyrachlor + fenoxaprop treatments. Tall fescue was not injured by any treatment. Results suggest aminocyclopyrachlor enhances fenoxaprop efficacy for smooth crabgrass control in tall fescue.
Methiozolin is a new isoxazoline herbicide being investigated for selective POST annual bluegrass control in creeping bentgrass putting greens. Glasshouse and field research was conducted from 2010 to 2012 in Tennessee and Texas to evaluate annual bluegrass control efficacy with methiozolin. Application placement experiments in the glasshouse illustrated that root absorption was required for POST annual bluegrass control with methiozolin at 1,000 g ai ha−1. Soil-plus-foliar and soil-only applications of methiozolin reduced annual bluegrass biomass greater than treatments applied foliar-only. Field experiments evaluated annual bluegrass control efficacy with two application rates (500 and 1,000 g ha−1) and six application regimes (October, November, December, October followed by [fb] November, November fb December, and October fb November fb December) on sand- and soil-based putting greens. Annual bluegrass control with methiozolin at 1,000 g ha−1 on sand-based greens ranged from 70 to 72% compared to 87 to 89% on soil-based greens. Treatment at 500 g ha−1 controlled annual bluegrass 57 to 64% on sand-based greens compared to 72 to 80% on soil-based greens. Most sequential methiozolin application regimes controlled annual bluegrass more than single applications. On sand-based greens, sequential application programs controlled annual bluegrass 70 to 79% compared to 85 to 92% on soil-based greens. Responses indicate that methiozolin is a root-absorbed herbicide with efficacy for selective control of annual bluegrass in both sand- and soil-based creeping bentgrass putting greens.
Indaziflam is a PRE herbicide for annual broadleaf and grass control in turfgrass systems and requires a 40-wk minimum interval between application and overseeding perennial ryegrass. Currently, activated-charcoal application is recommended to reduce that interval; however, preliminary evaluations determined activated charcoal alone was not a robust mitigation practice for successful establishment during perennial ryegrass overseeding. Field research was conducted in North Carolina and Tennessee to evaluate various mitigation practices to effectively overseed perennial ryegrass into indaziflam-treated turfgrass areas. Immediately following indaziflam application (53 g ai ha−1), two scenarios were created by delivering 0 or 0.3 cm H2O before mitigation practice. Irrigated plots were air-dried before conducting mitigation practices. Evaluated mitigation practices included scalping (0.6 cm cut height; debris removed), verticutting (1.25 cm depth; debris removed), and activated-charcoal application (167 kg ha−1 applied as an aqueous slurry in 3,180 L ha−1), evaluated individually and in each two-way combination in the order scalp followed by (fb) activated charcoal, scalp fb verticut, or verticut fb activated charcoal. Twenty-four hours after mitigation practice completion, perennial ryegrass was seeded (976 kg ha−1) and maintained as a golf course fairway. Overall, perennial ryegrass cover was reduced ≥ 93% at 8 and 20 wk after treatment (WAT) when no mitigation practices were performed. Stand-alone mitigation practices variably improved perennial ryegrass establishment; however, no practice provided acceptable results for end users. Combining mitigation practices improved overseeding establishment, most notably by adding activated charcoal application or verticutting to scalping before irrigation. Across experimental runs and locations, scalp fb activated-charcoal application before irrigation reduced perennial ryegrass cover 22 to 27% at 20 WAT. Results from this research suggest mitigation practices in addition to the currently recommended activated-charcoal application should be performed by turfgrass managers to improve perennial ryegrass overseeding establishment in indaziflam-treated turfgrass areas.
Herbicide applications prior to turf renovation often fail to provide complete control of perennial warm-season turfgrass species like seashore paspalum. Surface applications of dazomet at 506 kg/ha provided > 90% POST control of ‘SeaDwarf’ seashore paspalum turf in 2008. Although applications of glyphosate at 5.6 kg/ha or fluazifop-P-butyl at 0.42 kg/ha induced significant injury, these treatments provided < 40% POST control of SeaDwarf seashore paspalum turf 10 wk after initial treatment (WAIT) in 2008. A similar response was noted following applications of glyphosate plus fluazifop-P-butyl at rates of 5.6 kg/ha and 0.42 kg/ha, respectively. POST control following applications of glyphosate at 5.6 kg/ha plus fluazifop-P-butyl at 0.42 kg/ha, prior to applying dazomet at 506 kg/ha, was not different from that which was observed following applications of dazomet alone at 506 kg/ha. These data suggest that granular applications of dazomet alone, at 506 kg/ha, can be used to provide effective control of SeaDwarf seashore paspalum prior to renovation.
Glyphosate is regularly used to control annual bluegrass populations in
dormant bermudagrass turf. A population of annual bluegrass not controlled
by glyphosate at 840 g ha−1 (glyphosate resistant, GR) was
identified on a golf course in Humboldt, TN in 2010. Mature tillers of GR
plants were established in a greenhouse and treated with glyphosate at 0,
210, 420, 840, 1,680, 3,360, and 6,720 g ha−1. Mature tillers of
a biotype known to be susceptible to glyphosate (SS) were also established
in the greenhouse and subjected to the same treatments. At 14 d after
treatment (DAT), glyphosate controlled the SS biotype > 95% at rates >
420 g ha−1. Comparatively, the GR biotype was only controlled 76%
with glyphosate at 6,720 g ha−1. The rates required to provide
50% control (I50 values) for SS and GR biotypes were 236 and 2,812 g
ha−1 respectively, resulting in a resistance factor of 12.
Photochemical efficiency (Fv/Fm) values on SS plants treated with glyphosate at > 210 g
ha−1 measured 0.000 at 14 DAT, whereas Fv/Fm values on GR plants were not significantly different from the
untreated control with glyphosate rates ≤ 840 g ha−1 on the same
date. In laboratory experiments, the SS biotype accumulated greater
shikimate concentrations than the GR biotype 3 to 6 DAT. Future research
should evaluate strategies for managing GR and SS annual bluegrass with
alternative modes of action.
Annual bluegrass resistance to inhibitors of acetolactate synthase (ALS) and photosystem II (PSII) in managed turf has been confirmed in the southeastern United States. A biotype of annual bluegrass that had developed resistance (R) to the PSII inhibitor simazine was not controlled by POST applications of foramsulfuron or trifloxysulfuron in 2011 or 2012. In whole plant dose-response experiments, trifloxysulfuron, simazine, and indaziflam controlled a susceptible (S) population of annual bluegrass > 91% when applied POST to nontillering plants. However, trifloxysulfuron applications at 3.5 to 223 g ai ha−1 only controlled R annual bluegrass ≤ 40%. Similarly, simazine at 140 to 9,000 g ai ha−1 only controlled R annual bluegrass ≤ 20%. R annual bluegrass plants were more tolerant to indaziflam applied POST to leaf stage plants prior to tillering, as rates > 100 g ai ha−1 were needed to control R annual bluegrass ≥ 96%. No differences in the activity of ALS in R and S plants exposed to increasing foramsulfuron concentrations from 0 to 100 µM were detected suggesting that nontarget mechanisms could explain reduced efficacy of POST herbicide applications in whole plant dose-response experiments. Applications of indaziflam (35 to 70 g ha−1) and oxadiazon (2,240 to 4,500 g ai ha−1) effectively controlled R annual bluegrass when applied PRE. This biotype of R annual bluegrass is the first reported instance of a weed developing resistance to multiple modes of action in managed turf. Education is needed among turf managers regarding the consequences of exclusive use of the same herbicides for annual bluegrass control leading to the onset of herbicide resistance.
Field research was conducted in 2010 and 2011 to investigate the efficacy of herbicides for dallisgrass control when applied at various growing (GDD) or cooling degree day (CDD) –based application timings. Herbicide treatments included fluazifop-p-butyl (fluazifop; 105 g ai ha−1), mesotrione (280 g ai ha−1), tembotrione (92 g ai ha−1), topramezone (37 g ai ha−1), and tank mixtures of fluazifop plus mesotrione, tembotrione, or topramezone. Herbicide treatments were applied at either 75, 175, 375, 775 GDD, or 5 CDD. Treated plots were subjected to three tall fescue interseeding regimes: no seeding, seeding in spring, or seeding in fall (0, 353, and 353 kg pure live seed ha−1, respectively). In 2010, dallisgrass control from fluazifop applied at 75, 375, and 775 GDD was poor (< 50%) by 52 wk after treatment (WAT); in 2011, control from fluazifop application at these timings was higher (62 to 72%). When applied at 175 GDD or 5 CDD in 2010 and 2011, dallisgrass control from fluazifop ranged from 79 to 93% at 52 WAT. The addition of mesotrione, tembotrione, or topramezone to fluazifop did not affect dallisgrass control at any application timing, and control provided by these herbicides alone was low (< 65%). Interseeding tall fescue in the fall improved dallisgrass control from herbicides applied at 75 GDD in 2010 and 175, 375, and 775 GDD at 52 WAT in both years. Results suggest that timing of fluazifop applications at 175 GDD and 5 CDD enhances dallisgrass control.
Indaziflam controls annual grassy weeds by inhibiting cellulose biosynthesis. Research was conducted from 2008 to 2011 in Tennessee, Texas, and Georgia evaluating the efficacy of indaziflam for PRE and POST control of annual bluegrass in bermudagrass turf. In Texas, indaziflam at 30, 40, 50, and 60 g ai ha−1 applied PRE provided 93 to 100% annual bluegrass control through 28 wk after treatment. When applied PRE at 80 g ai ha−1 and at 4, 8, and 12 wk after PRE (WAP), indaziflam controlled annual bluegrass 67 to 100% 32 wk after initial treatment (WAIT) in Tennessee; however, reduced efficacy was observed with 12 WAP treatments in a single year of a 2-yr study. Similarly, annual bluegrass control with PRE applications or with 4 and 8 WAP applications of indaziflam at 35 and 52.5 g ai ha−1 ranged from 88 to 100% at 30 WAIT in Tennessee. In Georgia, these rates of indaziflam applied PRE and 4 WAP controlled annual bluegrass 96 to 100% on all evaluation dates and resulted in 97 to 100% reduction in plant counts relative to the untreated control at 30 WAIT. When applied 8 WAP, the 35 and 52.5 g ai ha−1 rates of indaziflam controlled annual bluegrass only 51 to 71% at 30 WAIT in Georgia. Although increasing the application rate of indaziflam treatments 8 WAP provided greater annual bluegrass control, each rate provided significantly lower control when applied 8 WAP compared with PRE or at 4 WAP. No bermudagrass injury was observed in this research. Results suggest indaziflam provides effective PRE and early POST control of annual bluegrass in bermudagrass turf. However, additional research is needed to determine the effects of plant size and maturity on indaziflam efficacy for POST annual bluegrass control.