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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 whereas sequential applications at either 70 + 70 g·ha followed by 35 + 35 g·ha or 52.5 + 52.5 g·ha followed by 52.5 + 52.5 g·ha 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). Pyrimisulfan is a sulfonanilide herbicidal inhibitor of ALS with structural similarity to bispyribac-sodium and pyrithiobac-sodium (Asakura et al., 2012). Pyrimisulfan is used for both preand postemergence weed control in rice (Oryza stricta L.) paddy fields (Yoshimura et al., 2013). Applications of pyrimisulfan at 50 to 75 g·ha effectively controlled Echinochloa spp., rock bulrush (Schoenoplectus juncoides), pickerel weed (Monochoria vaginalis), and Lindernia spp. in greenhouse trials (Asakura et al., 2012). Reduced efficacy of pyrimisulfan formulated as a ‘‘wettable’’ powder under flooded conditions common in rice production spurred the development of a controlled-release granular formulation (0.67%pyrimisulfan) designed to control weeds both preand postemergence (Asakura et al., 2012). A series of greenhouse experiments were conducted in Japan to compare weed control efficacy of this controlled-release granular formulation to a granular formulation of bensulfuronmethyl (0.75%) + bromobutide (9%) + pentoxazone (2%) + pyriminobac-methyl (4.5%) that is a standard herbicide used by Japanese rice producers (Asakura et al., 2012). Herbicides were applied at 10 kg·ha both preand postemergence with and without simulated flooding. Granular pyrimisulfan controlled 16 different weed species 96% to 100%when applied preemergence, including biotypes of pickerel weed and rock bulrush with target site resistance to sulfonylurea herbicides. Similarly, granular application of pyrimisulfan at an early postemergence timing (two to three leaves) controlled seven different weed species 90% to 100%, including two biotypes with confirmed resistance to sulfonylurea herbicides. Flooding did not affect efficacy of granular pyrimisulfan in either experiment whereas the standard of bensulfuronmethyl + bromobutide + pentoxazone + pyriminobac-methyl showed reduced efficacy for control of tidalmarsh flatsedge (Cyperus serotinus Rottb.), Scirpus nipponicus Makino, cosmopolitan bulrush [Bolboschoenus maritimus (L.) Palla], pigmy arrowhead (Sagittaria pygmaea Miq.), and threeleaf arrowhead (Sagittaria trifolia L.) under flooded conditions. Penoxsulam is an ALS inhibitor used for broadleaf weed control in managed turfgrass systems (Loughner et al., 2006). Penoxsulam provides early postemergence control of weeds such as white clover (Trifolium repens L.), buckhorn plantain (Plantago lanceolata L.), common dandelion (Taraxacum officinale L.), ground ivy (Glechoma hederacea L.), and virginia buttonweed (Diodia virginiana L.) at rates of 20 to 180 g·ha (Loughner et al., 2006). Interestingly, weed control efficacy of penoxsulam applied on a granular fertilizer carrier (average particle size, 0.5– 2.5 mm) exceeded applications formulated as liquids (Loughner et al., 2006). Penoxsulam is often applied in combination with other herbicides to widen the spectrum of weeds controlled by a single application. For example, Loughner and Nolting (2010) evaluated efficacy of penoxsulam + 2,4-D + dicamba (LockUp; Dow AgroSciences, Indianapolis, IN) for control of white clover and common dandelion at six locations in the northern United States over 2 years. The researchers found that the presence of foliar moisture at application increased efficacy. Synergy has been observed when combining penoxsulam with other ALS-inhibiting herbicides as well (Hufnagl and Mann, 2015). Weed control efficacy of granular pyrimisulfan is limited to grassy weed and tuber species of rice (Asakura et al., 2012). Penoxsulam is an effective option for earlypostemergence control of broadleaf weeds (Loughner et al., 2006). Considering that both pyrimisulfan and penoxsulam efficacy are improved when applied on a granular carrier, combining pyrimisulfan with penoxsulam may provide turfgrass managers a new option for broadleaf and sedge weed control in warm-season turfgrass. Hoyle (2017) reported that pyrimisulfan + penoxsulam was safe for use on both buffalograss (Bouteloua dactyloides, cv. Cody) and zoysiagrass (Zoysia japonica, cv. Meyer), and effectively controlled large crabgrass (Digitaria sanguinalis). However, there are no published reports on sedge and broadleaf weed control efficacy of pyrimisulfan + penoxsulam in warm-season turfgrass. We hypothesized that pyrimisulfan + penoxsulam could effectively control white clover, yellow nutsedge, wild violet (Viola spp.), ground ivy, and virginia buttonweed when applied at an earlypostemergence growth stage. Several field experiments were conducted during 2017 and 2018 to test this hypothesis. Materials and Methods Research sites. Field trials were conducted at the East Tennessee AgResearch and Education Center – Plant Sciences Unit, Knoxville, TN, from Apr. through Aug. 2017 and 2018. All trials were conducted in areas of common bermudagrass (Cynodon dactylon L.) or tall fescue (Festuca arundinacea Schreb.) turf established on Sequatchie silt loam soil (fine-loamy, siliceous, semiactive, thermic humic Hapludult) with pH values ranging from 5.7 to 6.7. Separate sites were used to evaluate treatment efficacy vs. natural infestations of white clover, yellow Received for publication 11 Oct. 2018. Accepted for publication 11 Feb. 2019. We acknowledge and thank PBI Corporation for their support of this research. We also thank Javier Vargas, Dallas Taylor, and Sydney Duncan for technical assistance throughout this project. Corresponding author. E-mail: jbrosnan@utk.edu. 960 HORTSCIENCE VOL. 54(5) MAY 2019 nutsedge, and virginia buttonweed; however, wild violet and ground ivy data were collected from a single site containing a mixed population of both species. Each year virginia buttonweed data were collected from a Riviera common bermudagrass fairway maintained at a 1.5-cm mowing height with a reel-mower (Reelmaster 5500D; The Toro Co., Bloomington, MN). Wild violet and ground ivy data were collected from a stand of tall fescue utility turf maintained at 8 cm with a rotary mower (Gravely 260Z; Gravely Tractor, Brillion, WI). White clover and yellow nutsedge data were collected from mixed stands of common bermudagrass and tall fescue maintained at 6 to 8 cm with the same aforementioned rotary mower. Irrigation was applied to supplement rainfall at all trial sites except the one used to collect wild violet and ground ivy data; this location received rainfall only. White clover control. Treatments evaluated for control of white clover included pyrimisulfan + penoxsulam (EH1580; PBI Gordon Corporation, Kansas City, MO) at 35 + 35 g·ha or 70 + 70 g·ha, as well as an untreated check. Both pyrimisulfan and penoxsulam were impregnated on a granular fertilizer at 0.025% (total herbicide load = 0.05%). The analysis of the fertilizer used for impregnation was 21% N : 0% P2O5 : 3% K2O, with N included in the form of polymercoated urea. Fertilizer particle size averaged 1.5 mm. Treatments were applied on 26 Apr. 2017 and 25 Apr. 2018 using a shaker jar. Experimental design was a randomized complete block with four replications of plots measuring 1.5 · 1.8 m in 2017 and 1.5 · 1.5 m in 2018. All treatments were irrigated into the soil within 24 h of application. Yellow nutsedge control. Treatments evaluated for control of yellow nutsedge included pyrimisulfan + penoxsulam at 35 + 35 g·ha or 70 + 70 g·ha applied singly, as well as sequential applications of 70 + 70 g·ha followed by 35 + 35 g·ha or 52.5 + 52.5 g·ha followed by 52.5 + 52.5 g·ha. An untreated check was included for comparison each year. Treatments were applied on the aforementioned granular fertilizer carrier on 26 Apr. 2017 and 25 Apr. 2018 using a shaker jar. Sequential applications were made with the same equipment on 30 May 2017 and 6 June 2018. Experimental design was a randomized complete block with four replications of plots measuring 1.5 · 1.8 m in 2017 and 1.5 · 2.1 m in 2018. All treatments were irrigated into the soil within 24 h of application. Wild violet and ground ivy control. Herbicide treatments evaluated on yellow nutsedge were also assessed for wild violet and ground ivy control each year. Treatment

Postemergence Weed Control in Warm-season Turfgrass with a Mixture of Pyrimisulfan and Penoxsulam