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- Author or Editor: J. Scott McElroy x
Siduron and quinclorac provide limited broadleaf weed control during seeded establishment of tall fescue. Carfentrazone and bromoxynil are contact herbicides that act primarily on broadleaf, dicot species. Research was conducted to evaluate tall fescue tolerance to carfentrazone or bromoxynil when integrated into traditional siduron and quinclorac weed control programs. Quinclorac at 0.84 kg·ha–1 applied at seeding followed by quinclorac at 0.84 kg·ha–1 35 days after emergence (DAE) and quinclorac at 1.68 kg·ha–1 plus carfentrazone at 0.034 kg·ha–1 applied DAE were the most injurious to tall fescue 42 and 49 DAE. While quinclorac sequential applications reduced turfgrass groundcover 42 DAE, tall fescue recovered by 49 DAE. Injury from all quinclorac treatments persisted until 63 DAE. Bromoxynil (0.28 or 0.56 kg·ha–1) or carfentrazone (0.017 or 0.034 kg·ha–1) caused minimal injury and no decrease in turfgrass groundcover when applied 35 DAE. While siduron applied at seeding followed by (fb) bromoxynil applied 35 DAE (6.7 fb 0.56 kg·ha–1) caused minimal tall fescue injury, a decrease in groundcover was observed at 49 DAE. No tall fescue cover reduction was observed for any treatment by 63 DAE. These data indicate that bromoxynil and carfentrazone can be safely used during seeded establishment of tall fescue beginning 35 DAE with no long-term effects on turfgrass stand development.
Research was conducted to evaluate the tolerance of tall fescue to mesotrione applied during establishment from seed. Nine field studies were conducted over a 3-year period (2004–2006) near Knoxville, Tenn., to evaluate the tolerance of seedling tall fescue [Schedonorus phoenix (Scop.) Holub] to mesotrione and quinclorac. The first evaluated tall fescue tolerance to single and sequential applications of mesotrione compared with quinclorac (multiple application study). The second evaluated the timing of mesotrione application on tall fescue injury and establishment (timing study). In the multiple application study, all treatments injured tall fescue 23% or less. Quinclorac reduced tall fescue groundcover up to 17% 63 days after emergence (DAE). Mesotrione at 0.28 kg·ha−1 applied 28 and 42 DAE or 14, 28, and 42 DAE decreased groundcover only 4% and 6% 63 DAE. In the timing study, mesotrione at 0.28 kg·ha−1 applied at 7 and 28 DAE injured tall fescue 17% to 21% 7 and 14 days after application; however, injury subsided to less than 10% by 28 days after application. Only mesotrione at 0.28 kg·ha−1 applied 7 DAE resulted in delayed tall fescue groundcover at 70 DAE. Variation was observed in Fall 2005 evaluations compared with other evaluations, which may be attributable to delayed seeding date and cool, wet conditions.
Centipedegrass (Eremochloa ophiuroides) is a low-maintenance, warm-season grass common throughout the southern United States. Slow establishment and growth rate of seeded centipedegrass often allows for increased weed competition, yet weed control options are limited. Tank-mixing simazine with mesotrione has been reported to improve weed control because of synergistic modes of action. A 2-year field trial was conducted to evaluate centipedegrass response to mesotrione and simazine applications applied 2 weeks after emergence. Mesotrione (0.25 lb/acre) did not reduce centipedegrass cover at any rating when applied alone. All rates of simazine, alone and tank-mixed with mesotrione, resulted in decreased centipedegrass cover 7 days after treatment (DAT). However, simazine alone at 0.25 lb/acre did not reduce turf cover 14, 28, and 49 DAT, and simazine at 0.25 lb/acre tank-mixed with mesotrione at 0.25 lb/acre did not reduce turf cover 28 and 49 DAT. Results indicate that newly established centipedegrass is vulnerable to cover reduction because of simazine and simazine plus mesotrione tank-mixture. Mesotrione and mesotrione tank-mixed with low rates of simazine is a viable option for newly seeded centipedegrass weed control; however, turf cover may be delayed.
Smooth crabgrass (Digitaria ischaemum) and goosegrass (Eleusine indica) are problematic weeds in creeping bentgrass (Agrostis stolonifera) because of limited herbicide options for postemergence (POST) control and turfgrass injury potential. Metamifop is a herbicide currently being considered for release to markets in the United States but information is lacking on the most effective rates and application timings for smooth crabgrass and goosegrass control in creeping bentgrass. Field trials were conducted in Auburn, AL in 2009 and 2013 to evaluate metamifop rates (200 to 800 g·ha−1) and single or sequential application timings compared with fenoxaprop (51 to 200 g·ha−1) at two different mowing heights. Metamifop applied twice and three times sequentially at 200 g·ha−1 provided the greatest smooth crabgrass (>97%) and goosegrass (>90%) control at rough (1½ inch) and green (1/8 inch) mowing heights without unacceptable creeping bentgrass injury at 56 days after initial treatment. All treatments caused <20% visible injury on creeping bentgrass at both mowing heights except the highest rate of metamifop. Smooth crabgrass control at the green mowing height was greater than at the rough mowing height, especially at lower metamifop rates with a single application.
Greenhouse studies were conducted to explore soil texture and planting depth effects on emergence of large crabgrass, Virginia buttonweed, and cock’s-comb kyllinga. Soil textures examined were sand, loamy sand, and clay loam with planting depths of 0, 0.5, 1, 2, 4, 6, and 8 cm. Percent emergence was standardized relative to surface emergence to allow comparisons among tested weed species. The three-way interaction of weed species, planting depth, and soil texture was never significant for emergence. Significant interactions occurred between weed species and soil texture, weed species and planting depth, and soil texture and planting depth. For all weed species and soil textures, emergence decreased as planting depth increased with the greatest percent emergence at the soil surface. The planting depth at which weed emergence was decreased 50% [relative to surface emergence (D50)] was predicted by regression analysis. Large crabgrass emerged from deepest depths (8 cm) followed by Virginia buttonweed (6 cm) and cock’s-comb kyllinga (2 cm). Large crabgrass, Virginia buttonweed, and cock’s-comb kyllinga D50 occurred at 3.9, 1.1, and 0.8 cm, respectively. Sand, loamy sand, and clay loam D50 occurred at 0.9, 2.3, and 1.9 cm, respectively, with D50 higher in the soils with greater water-holding capacity.
Carfentrazone is a broadleaf weed control herbicide that is also used for control of silvery-thread moss (Bryum argenteum) in creeping bentgrass (Agrostis stolonifera) putting greens. Field studies were initiated in June 2006 and May 2007 to evaluate silvery-thread moss control with carfentrazone alone, carfentrazone applied with nitrogen (N) and/or topdressing (TD), N alone, TD alone, and mancozeb plus copper hydroxide. All treatments except for mancozeb plus copper hydroxide and the non-treated control reduced silvery-thread moss populations 16 weeks after initial treatment. Carfentrazone applied alone and carfentrazone followed by N decreased silvery-thread moss populations by 39%. Carfentrazone followed by TD and carfentrazone followed by N + TD decreased silvery-thread moss populations by 73% and 66%, respectively. These data indicate the importance of using cultural practices to control silvery-thread moss on creeping bentgrass putting greens.
White clover (Trifolium repens L.) inclusion is a proposed means of increasing the sustainability of certain low-maintenance turfgrass scenarios through increased pollinator habitat and as a result of the legume’s ability to biologically fix atmospheric nitrogen (N). Proper white clover establishment is key to maximizing stand uniformity and N contribution to associated grasses. However, there are few guidelines for white clover establishment within warm-season turfgrasses. Four studies were conducted to evaluate seeded white clover establishment within a dormant hybrid bermudagrass [Cynodon transvaalensis Burtt-Davy × C. dactylon (L.) Pers.] lawn as affected by 1) pre-seeding mechanical surface disruption; 2) establishment timing; 3) seeding rate; and 4) companion grass species. White clover establishment was improved by scalping before October seeding, but these effects were not further enhanced by the addition of verticutting or hollow tine aerification. Unscalped turfgrass yielded nearly 50% lower white clover densities than those scalped before seeding, possibly as a result of decreased seed-to-soil contact and increased bermudagrass competition. January and February establishment dates generally yielded the lowest spring clover densities, whereas October timing yielded superior establishment. Clover densities resulting from six seeding rates (0, 0.4, 0.8, 1.5, 3.0, and 6.0 g live seed/m2) were fit to the linear model (y = y 0 + ax b , where y equals trifoliate leaves/m2 and x is equal to initial seeding rate). An important feature of this model was that it accurately represented the diminishing response of increasing seeding rate. Clover establishment was negatively correlated with companion grass densities with the largest densities occurring when planted with tall fescue and the smallest when planted with annual ryegrass. Ultimately, scalping alone or in combination with other mechanical surface disruption should be paired with a clover variety acceptable to the height of cut and the environmental conditions of individual scenarios. Likewise, seeding rates and the decision to include a cool-season companion grass species will be dependent on the use of a turf and the desired green cover.
Summer annual grassy weeds such as goosegrass (Eleusine indica L. Gaertn.) continue to be problematic to control selectively with postemergence (POST) herbicides within turfgrass stands. In recent years, reduced performance by certain herbicides (e.g., foramsulfuron), cancellation of goosegrass-specific herbicides (e.g., diclofop-methyl), and cancellation and/or severe use reductions of other herbicides [e.g., monosodium methanearsonate (MSMA)] have limited the options for satisfactory control and maintenance of an acceptable (≤30% visual turfgrass injury) turfgrass quality. Currently available herbicides (e.g., topramezone and metribuzin) with goosegrass activity typically injure warm-season turfgrass species. The objectives of this research were to evaluate both ‘Tifway 419’ bermudagrass [Cynodon dactylon (L.) Pers. ×Cynodon transvaalensis Burtt-Davy] injury after treatment with POST herbicides, and to determine whether irrigating immediately after application reduces turfgrass injury. Treatments were control (± irrigation); topramezone (Pylex 2.8C; ± irrigation); carfentrazone + 2,4-D + dicamba + 2-(2-methyl-4-chlorophenoxy) propionic acid (MCPP) (Speedzone 2.2L; ± irrigation); carfentrazone + 2,4-D + dicamba + MCPP in combination with topramezone (± irrigation); metribuzin (Sencor 75DF; ± irrigation); mesotrione (Tenacity 4L; ± irrigation); simazine 4L (±irrigation); and mesotrione + simazine (± irrigation). Irrigated treatments were applied immediately with a hand hose precalibrated to apply 0.6 cm or 0.25 inch (≈6.3 L). Visual turfgrass injury for combined herbicide treatments for the irrigated plots was 6% 4 days after treatment (DAT), 12% 1 week after treatment (WAT), 17% 2 WAT, and 6% 4 WAT, whereas nonirrigated plots had turfgrass injury of 14% at 4 DAT, 31% 1 WAT, 35% 2 WAT, and 12% 4 WAT. Irrigated pots had normalized differences vegetative indices (NDVI) ratings of 0.769 at 4 DAT, 0.644 at 1 WAT, 0.612 at 2 WAT, and 0.621 at 4 WAT, whereas nonirrigated plots had the lowest (least green) turfgrass NDVI ratings of 0.734 at 4 DAT, 0.599 at 1 WAT, 0.528 at 2 WAT, and 0.596 at 4 WAT. These experiments suggest turfgrass injury could be alleviated by immediately incorporating herbicides through irrigation.
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.
Heat-tolerant bluegrass varieties were developed to resist dormancy and retain pigmentation during heat stress events. The objective of this study was to investigate the influence of grass species, nitrogen (N) fertilization, and seasonality on the accumulation patterns of lutein, β-carotene, and chlorophyll a and b in the leaf tissues of turfgrass. The heat-tolerant bluegrass cultivars Dura Blue and Thermal Blue (Poa pratensis L. × Poa arachnifera Torr.), Apollo kentucky bluegrass (Poa pratensis L.), and Kentucky 31 tall fescue (Festuca arundinacea Schreb.) were compared for the accumulation of plant pigments. Evaluations were conducted over 2 consecutive years (Years 4 and 5 after establishment) during two different seasons (spring and summer) and under varying N fertilization. Fertilizer applications of 5, 14, and 27 g N/m2/year resulted in a significant positive correlation for the accumulation of leaf blade lutein and chlorophyll a and b, but not for β-carotene. The accumulation of the four measured plant pigments among the grasses was significantly different with ‘Apollo’ having the largest concentration of pigments followed by ‘Dura Blue’, ‘Thermal Blue’, and finally ‘Kentucky 31’. Specifically, when comparing the cultivars Apollo and Kentucky 31, the pigment levels decreased 27%, 26%, 26%, and 23% for lutein, β-carotene, and chlorophyll a and b, respectively. The interesting observation of the analysis of the grass pigment concentrations was that the least reported heat-tolerant cultivar in our study (‘Apollo’) had the largest measured pigment concentrations.