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Michael W. Smith, Margaret E. Wolf, Becky S. Cheary, and Becky L. Carroll

Two studies were conducted to determine if selected grass and dicot species had an allelopathic interaction with pecan (Carya illinoinensis Wangenh. C. Koch). Leachate from pots with established grasses or dicots was used to irrigate container-grown pecan trees. Leachates from bermudagrass [Cynodon dactylon (L.) Pers.], tall fescue (Festuca arundinacea Shreb. cv. Kentucky 31), redroot pigweed (Amaranthus retroflexus L.), and cutleaf evening primrose (Oenothera laciniata Hill) reduced leaf area and leaf dry weight about 20% compared to the controls. Bermudagrass, tall fescue, and primrose leachate decreased pecan root weight 17%, trunk weight 22%, and total tree dry weight 19% compared to the control. In a second study, trees were 10% shorter than the control when irrigated with bermudagrass or pigweed leachate.

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S.K. Braman, R.R. Duncan, and M.C. Engelke

Turfgrass selections including 21 paspalums (Paspalum vaginatum Swartz) and 12 zoysiagrasses (Zoysia sp.) were compared with susceptible `KY31' tall fescue (Festuca arundinacea Schreb.) and more resistant common bermudagrass (Cynodon dactylon Pers.) and common centipedegrass [Eremochloa ophiuroides (Munro.) Hack] for potential resistance to fall armyworm [Spodoptera frugiperda (J.E. Smith)], an occasionally serious pest of managed turf. Turfgrass and pasture grasses annually suffer sporadic damage by this pest, often severe in the Gulf Coast states. Resistant grasses offer an alternative management tool for the fall armyworm, reducing the need for pesticide use. Laboratory evaluations assessed the degree of antibiosis and nonpreference present among more than 30 turfgrass genotypes to first and third instar fall armyworms, respectively. Zoysiagrasses exhibiting high levels of antibiosis included `Cavalier', `Emerald', DALZ8501, DALZ8508, `Royal', and `Palisades'. Paspalum selections demonstrating reduced larval or pupal weights or prolonged development times of fall armyworm included 561-79, Temple-2, PI-509021, and PI-509022.

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R.N. Carrow and B.J. Johnson

A turfgrass wear injury study was conducted at Griffin, Ga., on `Tifway' bermudagrass (Cynodon dactylon × C. transvaalensis) using two golf car tires and three golf car types driven in a semicircular pattern to deliver 85 passes over the tread path plot area. Wear injury for the 14 days after wear was applied was assessed by visual quality, percent green coverage, leaf bruising, and verdure. Golf tire × car interactions occurred, but more wear occurred with the low pressure (48 × 103 Pa), dimpled tread tire with flexible sidewalls than the commonly used bias ply (4-ply), V-shaped tread tire with more rigid sidewalls. Significant differences in wear damage occurred for golf car type but were influenced by tire design. Thus, selection of golf car tire and golf car type can influence the degree of wear injury on turfgrass sites.

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Robert E. Rouse and J. Jeffrey Mullahey

A 2-year establishment study of perennial peanut (Arachis glabrata Benth.) planted in row middles of a 1-year-old citrus grove was initiated in southwest Florida. The effect of herbicide and fertilizer treatment combinations on perennial peanut density was measured. Treatments were Fluazifop-p-butyl (Fusilade 2000 1E) herbicide, K-Mag fertilizer, Fluazifop-p-butyl + K-Mag + N, and a nontreated control. Four replications were arranged in a randomized complete-block design. After 2 years, there were no significant differences in plant density between treatments (96% cover) and the control (89% cover). Applications of Fluazifop-p-butyl in years one and two were effective in controlling grassy weeds such as common bermudagrass [Cynodon dactylon (L.) Pers]. In this experiment. initiated 1 year after planting, perennial peanut without inputs (herbicide, fertilizer) was able to suppress common bermudagrass and to obtain a high level (89%) ground cover in 3 years (1991–94).

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B. Jack Johnson

A field study was conducted to assess the effects of N and Fe with trinexapac-ethyl (TE) on established `Tifway' bermudagrass (Cynodon dactylon × C. transvaalensis) during 2 years at Griffin, Ga. There were no TE × Fe or N treatment interactions when applied in three applications at 4-week intervals each year. Combinations of Fe with TE improved turfgrass quality over TE alone at 1 to 2 weeks after each treatment. The improvement from Fe sources was 17 % higher with Sprint 300 and SoluPlex, 33% higher with Ferromec and LawnPlex, and 67% higher with ferrous sulfate. Vegetative suppression of `Tifway' bermudagrass at 14 weeks after treatment ranged from 46% in 1994 to 28% in 1995 when treated with TE at 0.1 kg·ha-1 in three applications at 4-week intervals. Neither N or Fe influenced vegetative growth when applied with TE. Chemical name used: 4 (cyclopropyl-α-hydroxy-methylene)-3.5-dioxocyclohexanecarboxlic acid ethyl ester (trinexapac-ethyl).

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C. Scott, R.K. Nishimoto, and C.S. Tang

Cyperus kyllingia and Cyperus brevifolius are problematic turfgrass weeds in Hawaii. Both are closely related weed species with similar morphology and growth characteristics. C. kyllingia appears to be a more successful weed with regards to interference than C. brevifolius. Greenhouse experiments were conducted to compare the levels of interference exerted by C. kyllingia and C. brevifolius upon Cynodon dactylon turfgrass. C. kyllingia reduced the growth of C. dactylon by about 50 %, while C. brevifolius did not significantly reduce C. dactylon growth. These results correspond with the chemical profiles of C. kyllingia and C. brevifolius. Analysis has shown that C. kyllingia contains two sesquiterpenes which have been identified as potentially allelopathic components of Cyperus rotundus. C. brevifolius contains waxes and the two sesquiterpenes found in C. kyllingia are absent. This suggests that allelopathy may be the mechanism responsible for the different levels of interference exhibited by C. kyllingia and C. brevifolius, and these species may provide an important model for the study of allelopathy.

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Michael W. Smith, Becky S. Cheary, and Becky L. Carroll

Newly planted pecan (Carya illinoinensis Wangenh. C. Koch cv. Kanza) trees were grown for 5 years in a bermudagrass [Cynodon dactylon (L.) Pers.] sod with vegetation-free circles 0, 0.91, 1.83, 3.66, or 7.32 m in diameter. Trees were irrigated and fertilized to minimize growth differences associated with competition from the bermudagrass. There were no differences in trunk diameter among treatments the first 2 years of the study. During the next 3 years, trunk diameter increased curvilinearly as the vegetation-free circle increased. A vegetation-free circle diameter of 1.83 m produced near maximum tree growth. Although trunk diameter improved slightly as the vegetation-free diameter was increased up to 7.32 m, it was not sufficient to justify the additional expense for herbicides nor exposure of unprotected soil to erosion.

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Laurie E. Trenholm, Darin W. Lickfeldt, and William T. Crow

This research was conducted to determine if application of 1,3-dichloropropene (1,3-D) could reduce turfgrass water requirements in soil infested with sting nematodes (Belonolaimus longicaudatus Rau). The effects of 1,3-D and fenamiphos were evaluated on quality and persistence of `Tifway 419' bermudagrass (Cynodon dactylon × C. transvaalensis Burtt-Davy) subjected to drought or deficit irrigation. The research consisted of two greenhouse studies in 2002 and 2003 where irrigation was either withheld or applied in deficit quantities, and one field study in 2003 where irrigation was withheld. In general, 1,3-D-treated turf maintained up to 40% higher quality during drought than other treatments and had up to 27% less leaf wilting. As drought severity increased, 1,3-D treatments had better spectral reflectance values, indicating better physiological functioning under stress. Results of this research suggest that application of 1,3-D in sting nematode-infested soils may increase bermudagrass drought survival.

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W.G. Foshee, W.D. Goff, K.M. Tilt, J.D. Williams, J.S. Bannon, and J.B. Witt

Organic mulches (leaves, pine nuggets, pine straw, grass clippings, and chipped limbs) were applied at depths of 10, 20, or 30 cm in a 3 × 3-m area around young pecan [Carya illinoinensis (Wangenh.) K. Koch] trees. These treatments were compared to an unmulched herbicide treatment and a common bermudagrass [Cynodon dactylon (L.) Pers.] sod. Trunk cross-sectional areas (TCSAs) of the mulched trees were larger than those of trees in the sod or unmulched plots and increased linearly as mulch depth increased. All mulches influenced TCSA similarly. Mean TCSA for mulched trees increased 14-fold compared to an increase of 8-fold for the unmulched trees and the sod in this 3-year study. Thus, common yard-waste mulches can be used effectively to increase growth of young pecan trees.

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Edward W. Bush, James N. McCrimmon, and Allen D. Owings

Four warm-season grass species [common carpetgrass (Axonopus affinis Chase), common bermudagrass (Cynodon dactylon [L.] Pers.), St. Augustinegrass (Stenophrum secondatum Walt. Kuntze.), and zoysiagrass (Zoysia japonica Steud.)] were established in containers filled with an Olivia silt loam soil for 12 weeks. Grasses were maintained weekly at 5 cm prior to the start of the experiment. Water stress treatments consisted of a control (field capacity), waterlogged, and flooded treatments. Waterlogging and flood treatments were imposed for a period of 90 days. The effects of water stress was dependent on grass species. Bermudagrass vegetative growth and turf quality were significantly reduced when flooded. Carpetgrass, St. Augustingrass, and zoysiagrass quality and vegetative growth were also reduced by flooding. St. Augustinegrass and zoysiagrass root dry weight was significantly decreased. Zoysiagrass plants did not survive 90 days of flooding. Leaf tissue analysis for common carpetgrass, common bermudagrass, St. Augustinegrass, and zoysiagrass indicated that plants subjected to waterlogging and flooding had significantly elevated Zn concentrations.