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Pyrimisulfan is a sulfonanilide herbicidal inhibitor of acetolactate synthase (ALS) used to control grass and sedge weeds of rice (Oryza stricta L.) production. Penoxsulam is an ALS-inhibiting herbicide that provides early postemergence control of broadleaf weeds in managed turfgrass. Separate field trials were conducted in Knoxville, TN, during Summer 2017 and 2018 to evaluate the efficacy of pyrimisulfan + penoxsulam for control of white clover (Trifolium repens L.), yellow nutsedge (Cyperus esculentus L.), wild violet (Viola spp.), ground ivy (Glechoma hederacea L.), and virginia buttonweed (Diodia virginiana L.) in common bermudagrass (Cynodon dactylon L.) and tall fescue (Festuca arundinacea Schreb.) turf. All treatments were applied on a granular fertilizer carrier (mean particle size, 1.5 mm) that contained 21% N : 0% P₂O₅ : 3% K₂O. Treatments were applied at an early postemergence growth stage during April of each year and were irrigated into the soil within 24 hours of application. Weed control was assessed from 4 to 10 weeks after initial treatment (WAIT) relative to untreated control plots in each replication. White clover and wild violet were controlled effectively with pyrimisulfan + penoxsulam at 70 + 70 g·ha⁻¹ whereas sequential applications at either 70 + 70 g·ha⁻¹ followed by 35 + 35 g·ha⁻¹ or 52.5 + 52.5 g·ha⁻¹ followed by 52.5 + 52.5 g·ha⁻¹ were needed to control yellow nutsedge, ground ivy, and virginia buttonweed effectively. Future research should explore long-term control of these species, particularly wild violet, ground ivy, and virginia buttonweed with pyrimisulfan + penoxsulam applied over multiple seasons. Chemical names: 2′-[(4,6-dimethoxypyrimidin-2-yl)(hydroxy) methyl]-1,1-difluoro-6′-(methoxymethyl)methanesulfonanilide (pyrimisulfan); 2-(2,2-difluoroethoxy)-N-(5,8-dimethoxy1,2,4triazolo 1.5-c-pyrimidin-2-yl)-6-(trifluoromethyl)benzenesulfonamide (penoxsulam).

Research was conducted to determine the tolerance of multiple native and ornamental grass species and one ornamental sedge species to over-the-top applications of the postemergence herbicide topramezone at three locations in the southeastern United States in 2016 and 2017. Fully rooted liners of selected grass species were outplanted into research plots in Apopka, FL; Dallas, TX; and Knoxville, TN in late spring, allowed time to establish (≈1–2 months) and then treated with two applications of topramezone at either 0.05 or 0.10 kg a.i./ha at 6–8 weeks intervals. Results showed that species including Andropogon virginicus (broomsedge), Schizachyrium scoparium ‘The Blues’ (little bluestem), Tripsacum dactyloides (eastern gamagrass), and Tripsacum floridanum (florida gamagrass) exhibited the greatest tolerance to topramezone with <10% injury to no injury being evident after each application of both herbicide rates tested. Chasmanthium latifolium (wild oats), Eragrostis elliottii ‘Wind Dancer’, Muhlenbergia capillaris (pink muhly), and Spartina bakeri (sandcord grass) were significantly injured (50% injury or greater) at both herbicide rates. Average injury observed on Panicum virgatum ‘Shenandoah’ (red switchgrass) (ranging from 39% to 100% injury) and Sorghastrum nutans (indian grass) (ranging from 0% to 40% injury) was higher in Florida than in Tennessee (injury ranging from 23% to 43% on red switchgrass and 0% to 10% on indian grass). Similarly, Pennisetum alopecuroides (dwarf fountain grass) showed higher tolerance in Texas (ranging from 0% to 34% injury) compared with those observed in Tennessee (ranging from 0% to 53% injury). Topramezone injury to Carex appalachica (appalachian sedge) was ≤18% following two applications at both rates tested. Although no injury was observed in appalachian sedge following a single application up to 0.1 kg a.i. in Florida, plants succumbed to heat stress and accurate ratings could not be taken following the second application. Because of variability observed, tolerance of red switchgrass, indian grass, dwarf fountain grass, and appalachian sedge to applications of topramezone deserves further investigation. There is potential for future use of topramezone for control of certain grass and broadleaf weeds growing in and around certain ornamental grass species. However, as there was significant variability in tolerance based on species and differences in cultivars, testing a small group of plants before large-scale application would be recommended.

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).

Turf managers applying amicarbazone for annual bluegrass (Poa annua L.) control in cool-season turfgrasses may wish to reseed into treated areas. Field experiments were conducted in Georgia and Tennessee to investigate perennial ryegrass (Lolium perenne L.) and tall fescue (Festuca arundinacea Schreb.) reseeding intervals after amicarbazone applications. Perennial ryegrass and tall fescue cover were reduced similarly (less than 10% from the untreated) by all herbicides applied 2, 4, or 6 weeks before seeding. Bispyribac-sodium at 0.1 kg a.i./ha reduced tall fescue and perennial ryegrass cover more than amicarbazone at 0.1 or 0.2 kg a.i./ha when applied the day of seeding. Applied on the day of seeding in Georgia, amicarbazone at 0.4 kg·ha⁻¹ reduced turf cover of each species similar to bispyribac-sodium; however, this response was not observed in Tennessee. Results suggest tall fescue and perennial ryegrass can be safely seeded the day of amicarbazone applications at 0.1 or 0.2 kg·ha⁻¹, but practitioners may need to wait 2 weeks before seeding these turfgrasses into areas treated with amicarbazone at 0.4 kg·ha⁻¹ or bispyribac-sodium at 0.1 kg a.i./ha.

Mesotrione, topramezone, and tembotrione are inhibitors of the enzyme p-hydroxyphenylpyruvate dioxygenase (HPPD), which impacts the carotenoid biosynthetic pathway. An experiment was conducted to determine the effects of mesotrione, topramezone, and tembotrione on carotenoid pigment concentrations in common bermudagrass [Cynodon dactylon (L.) Pers.; cv. Riviera] leaf tissues. Bermudagrass plants were treated with three rates of mesotrione (0.28, 0.35, and 0.42 kg·ha⁻¹), topramezone (0.018, 0.025, and 0.038 kg·ha⁻¹), and tembotrione (0.092, 0.184, and 0.276 kg·ha⁻¹). The lowest rate of each herbicide represented the maximum labeled use rate for a single application. Percent visual bleaching was measured at 3, 7, 14, 21, 28, and 35 days after application (DAA). Leaf tissues were sampled on the same dates and assayed for carotenoids. Topramezone and tembotrione bleached bermudagrass leaf tissues to a greater degree than mesotrione. Concomitantly, topramezone and tembotrione also reduced total chlorophyll (chlorophyll a + b), β-carotene, lutein, and total xanthophyll cycle pigment concentrations (zeaxanthin + antheraxanthin + violaxanthin) more than mesotrione. Increases in visual bleaching resulting from application rate were accompanied by linear reductions in lutein, β-carotene, and violaxanthin for all herbicides. Topramezone and tembotrione increased the percentage of zeaxanthin + antheraxanthin in the total xanthophyll pigment pool (ZA/ZAV) 7 days after peak visual bleaching was observed at 14 DAA. Reductions in ZA/ZAV were reported after 21 DAA. This response indicates that sequential applications of topramezone and tembotrione should be applied on 14- to 21-day intervals, because stress induced by these herbicides is greatest at these timings. Increases in photoprotective xanthophyll cycle pigments (ZA/ZAV) at 14 to 21 DAA may be a mechanism allowing bermudagrass to recover from HPPD-inhibiting herbicide injury, because bermudagrass recovered from all treatments by 35 DAA. Data in the current study will allow turf managers to design physiologically validated bermudagrass control programs with HPPD-inhibiting herbicides. Chemical names: mesotrione [2-(4-methysulfonyl-2-nitrobenzoyl)-1,3-cyclohexanedione], tembotrione {2-[2-chloro-4-(methylsulfonyl)-3-[(2,2,2-(trifluoroethoxy)methyl]benzoyl]-1,3-cyclohexanedione}, topramezone {[3-(4,5-dihydro-3-isoxazolyl)-2-methyl-4-(methylsulfonyl)phenyl](5-hydroxy-1-nethyl-1H-pyrazol-4-yl)methanone}.

Turfgrass managers applying aminocyclopyrachlor for annual and perennial broadleaf weed control in cool-season turfgrasses may want to reseed into treated areas. Field experiments were conducted in Georgia), Tennessee, and Texas to investigate perennial ryegrass (Lolium perenne L.) and tall fescue (Festuca arundinacea Schreb.) reseeding intervals after aminocyclopyrachlor applications. Perennial ryegrass and tall fescue establishment were similar to the non-treated control after treatments of aminocyclopyrachlor and 2,4-dichlorophenoxyacetic acid (2,4-D) + dicamba + methylchlorophenoxypropionic acid (MCPP) at 0, 2, 4, or 6 weeks before seeding. Results demonstrate that no reseeding interval is required after aminocyclopyrachlor treatment. Perennial ryegrass and tall fescue can be safely seeded immediately after aminocyclopyrachlor treatment at 39, 79, and 158 g/a.i./ha.

Data describing effects of plant growth regulator (PGR) applications on bermudagrass (Cynodon spp.) traffic tolerance are limited. A 2-year study was conducted evaluating effects of several PGRs on ‘Riviera’ bermudagrass (Cynodon dactylon L.) traffic tolerance. Treatments included 1) ethephon at 3.8 kg·ha⁻¹; 2) trinexapac-ethyl (TE) at 0.096 kg·ha⁻¹; 3) paclobutrazol at 0.28 kg·ha⁻¹; 4) flurprimidol at 0.0014 kg·ha⁻¹; 5) flurprimidol + TE at 0.0014 kg·ha⁻¹ + 0.096 kg·ha⁻¹, respectively; 6) ethephon + TE at 3.8 kg·ha⁻¹ + 0.096 kg·ha⁻¹, respectively; and 7) untreated control. All treatments were applied three times on a 21-d interval before trafficking. Plots were subjected to three simulated football games per week with the Cady Traffic Simulator. Traffic began 2 weeks after the last sequential application of each PGR. Turfgrass color, quality, and cover were quantified weekly using digital image analysis. Turfgrass cover measurements were used to assess traffic tolerance. Improvements in turfgrass color, quality, and cover were observed with applications of TE, ethephon + TE, and flurprimidol + TE. Turfgrass color, quality, and cover were enhanced for ethephon + TE and flurprimidol +TE compared with applications of ethephon and flurprimidol alone. Considering that no differences in turfgrass color, quality, or cover were detected among TE, ethephon + TE, and flurprimidol + TE at any time in the study, the responses observed suggest that TE may have a greater impact than other PGRs on ‘Riviera’ bermudagrass athletic field turf when applied before traffic stress. Chemical names used: rthephon (2-chloroethyl)phosphonic acid; glurprimidol {α-(1-methylethyl)-α-[4-(trifluoro-methoxy) phenyl] 5-pyrimidine-methanol}; paclobutrazol, (+/−)-(R*,R*)-β-[(4-chlorophenyl) methyl]-α-(1–1-dimethyl)-1H-1,2,4,-triazole-1-ethanol; trinexapac-ethyl [4-(cyclopropyl-[α]-hydroxymethylene)-3,5-dioxo-cyclohexane carboxylic acid ethyl ester].

Mesotrione {2-[4-(methylsulfonyl)-2-nitrobensoyl]-1,3-cyclohexanedione} is a herbicide that indirectly inhibits phytoene desaturase in plant tissues, the first step in the carotenoid biosynthesis pathway. The predominant symptom of mesotrione activity is tissue whitening with subsequent plant necrosis. In the current study, ‘Riviera’ bermudagrass [Cynodon dactylon (L.) Pers.] was treated with mesotrione at 0.28 kg·ha⁻¹ or untreated and sampled for tissue pigment concentrations at 0, 3, 7, 14, 21, 28, and 35 days after treatment (DAT). Visual tissue whitening in mesotrione-treated plants reached a maximum of 38% by 14 DAT; however, regreening of discolored tissue was observed by 21 DAT. Phytoene was only detected in mesotrione-treated plants at 3, 7, and 14 DAT. Pigments in treated plants decreased with initial tissue whitening; however, most recovered to untreated levels by 21 DAT. At 35 DAT, chlorophyll a, chlorophyll b, lutein, β-carotene, and zeaxanthin in mesotrione-treated plants had accumulated to levels exceeding untreated control plants. Results demonstrate that although mesotrione initially decreases bermudagrass pigment concentrations, treatment with this herbicide eventually results in higher concentrations of chlorophylls and carotenoids.

Imazapic is an acetolactate synthase-inhibiting herbicide labeled for weed control in pastures, rangeland, and noncrop areas. Field research was conducted in Knoxville, TN, USA, during 2020 and 2021 to evaluate the tolerance of four hybrid bermudagrass (Cynodon dactylon × Cynodon transvaalensis Burtt Davy) cultivars to applications of imazapic for growth suppression. Separate experiments were conducted on ‘TifTuf’, ‘Tifway’, ‘Tahoma 31’, and ‘Latitude 36’ hybrid bermudagrass. Experiments included plots (1.5 m²) arranged in a randomized complete block design with four replications and were repeated. Treatments were applied 14 Aug 2020 and 6 Aug 2021, and were mixed with methylated seed oil. Imazapic rates were 0, 35, 52.5, 70, or 105 g⋅ha^–1. Cultivar tolerance was assessed via visual ratings of turfgrass injury relative to untreated check plots. Normalized differential vegetation index data were collected on each date turfgrass injury was evaluated. Growth suppression was quantified via reductions in dry clipping weight after mowing. Hybrid bermudagrass injury increased with imazapic rate for all cultivars, and peak injury (> 30%) following all imazapic treatments occurred within 14 days. At the lowest imazapic rate (35 g⋅ha^–1), injury was transient, with all hybrid bermudagrass cultivars fully recovered by 28 days. All rates of imazapic reduced hybrid bermudagrass dry clipping weight for 21 days for all cultivars. Further research is warranted to explore lower application rates than those tested in our study, in addition to determining tolerance and growth suppression of other turfgrass species commonly managed on golf courses.

Divoting is a common occurrence on golf courses and athletic fields. Research was conducted at the University of Tennessee Center for Athletic Field Safety (Knoxville, TN) during 2012–13 evaluating the effects of preemergence (PRE) herbicide applications on hybrid bermudagrass [C. dactylon (L.) Pers. × C. transvaalensis Burtt-Davy, cv. Tifway] divot resistance and recovery. Plots were subjected to the factorial combination of seven herbicide treatments (indaziflam at 35 and 52.5 g·ha⁻¹; prodiamine at 840 g·ha⁻¹; pendimethalin at 3360 g·ha⁻¹; dithiopyr at 560 g·ha⁻¹; oxadiazon at 3360 g·ha⁻¹; non-treated control) and three divot timings [1, 2, and 3 months after herbicide treatment (MAT)]. Rates were based on label recommendations for preemergence crabgrass (Digitaria spp.) control. Herbicides were applied on 15 Mar. 2012 and 2013. Divots were generated using a weighted pendulum apparatus designed to impart 531 J of impact energy to the turf sward with a golf club. Divot resistance was quantified by measuring divot volume at each timing while divot recovery was quantified by measuring turf cover in the divot scar using digital image analysis. All herbicide-treated plots produced divots with volumes ≤ the non-treated control. In 2013, volumes were greater for divots produced 1 MAT (215 cm³) than those created 2 MAT (191 cm³) or 3 MAT (157 cm³). No differences in divot recovery were detected as a result of herbicide treatment in either year. Under the conditions of this study, applications of PRE herbicides at labeled rates did not affect divot resistance or recovery.

Chemical names: N-[(1R,2S)-2,3-dihydro-2,6-dimethyl-1H-inden-1-yl]-6-(1-fluoroethyl)-1,3,5-triazine-2,4-diamine (indaziflam), 2,4 dinitro-N3,N3-dipropyl-6-(trifluoromethyl)-1,3-benzenediamine (prodiamine), N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine (pendimethalin), S,S-dimethyl 2-(difluoromethyl)-4-(2-methylpropyl)-6-(trifluoromethyl)-3,5-pyridinedicarbothioate (dithiopyr), 3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethylethyl)-1,3,4-oxadiazol-2-(3H)-one (oxadiazon)