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A field study was conducted in southern Louisiana to screen several plant growth regulators (PGRs) for efficacy in suppressing centipedegrass [Eremochloa ophiuroides (Munro) Hack.] vegetative growth and seedhead production. PGRs were applied in three sequential treatments in 1988 and included ethephon, glyphosate, mefluidide, paclobutrazol, sethoxydim, and sulfometuron methyl. Ethephon (5.0 kg·ha-1) suppressed mean centipedegrass vegetative growth by 15% with no turf injury. Mefluidide (0.6 kg·ha-1) and ethephon reduced mean seedhead number by 55% and 61%, respectively. Glyphosate (0.6 kg·ha-1) suppressed vegetative and reproductive growth, but caused unacceptable phytotoxicity and reduced centipedegrass cover and quality during Spring 1989. Use of ethephon or mefluidide to reduce trimming requirements or mower operation in hazardous areas may be an effective means of inhibiting centipedegrass growth. Chemical names used: N -(phosphonomethyl) glycine (glyphosate); N -[2,4-dimethyl-5-[[(trifluromethyl) sulfonyl]amino] phenyl]acetimide (mefluidide); 2-[1-(ethoxyimino)butyl] -5[2-(ethylthio) propyl]-3-hydroxy-2-cycIohexen-l-one (sethoxy-dim); 2-[[[[(4,6-dimethyl-2 -pyrimidinyl) amino] carbonyl]amino] sulfonyl]benzoic acid (sulfometuron methyl); (2-chloroethyl) phosphoric acid (ethephon); (±)-(R*R*)β-[(4-chlorophenyl)methyl]-α-(l,l-dimethylethyl) -1 H -l,2,4-triazole-l-ethanol (paclobutrazol).

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Abstract

Small weighing lysimeters were used to determine potential evapotranspiration (ET) (i.e., ET when soil water is not limiting) rates of turf weeds and ground-covers. When ET was monitored during two consecutive summers, white clover (Trifolium repens L.) had the highest mean water use rate (7.4 mm·day-1). Dichondra (Dichondra repens J.R. Forst. and G. Forst.), a low-growing C4 dicot, and barnyardgrass [Echinochloa crusgalli (L.) Beauv.], a C4 monocot, used the least water (3.9 and 4.1 mm·day-1, respectively). ‘Merion’ Kentucky bluegrass (Poa pratensis L.), a C3 species, and yellow foxtail [Setaria glauca (L.) Beauv.] and smooth crabgrass [Digitaria ischaemum (Schreb.) Muhl.], C4 species, exhibited intermediate ET rates. Water use rates of these ground-covers should be considered when using them in landscapes. Eradication of some weeds, such as white clover, in well-watered turf areas may be an effective means of reducing ET.

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Abstract

Field and greenhouse studies were conducted to determine effects of deficit irrigation and pre-plant soil incorporation of a hydrophilic polymer on the establishment of ‘Rebel’ tall fescue. In the field, lysimeters containing a sandy clay loam soil were seeded with tall fescue and irrigated with equivalents of 50% or 100% of the potential evapotranspiration (ETp) (i.e., water used when soil moisture is not limiting) of a mature turf. The low irrigation level resulted in poor germination and stand establishment. Pre-plant incorporation of a hydrophilic polymer (98 kg·ha-1) was ineffective in enhancing seedling survival under dry soil conditions. Greenhouse studies evaluating higher levels of polymer application on tall fescue establishment during drought revealed that the polymer did not reduce plant stress until occupying at least 1.0% of the soil volume to a depth of 12.5 cm. Excessive polymer amounts would be required to achieve this proportion in the field.

Open Access

Abstract

Potential evapotranspiration (ET) (i.e., ET when soil water is not limiting) rates of creeping bentgrass (Agrostis palustris Huds.) and annual bluegrass (Poa annua L.) were determined during two consecutive summers using weighing lysimeters in the field. When evaluated under putting green conditions, significant species differences in ET were observed during several weeks in 1985 and 1986. Differences were small, however, and irrigation requirements should not vary much between these species. Both species exhibited lower water use rates in 1986 when cut at 6 mm (4.6 mm·day-1) than at 12 mm (4.9 mm·day-1). These small differences should not greatly affect water requirements of putting green turf maintained at variable cutting heights. Variability of ET throughout the study periods suggests that water savings could result if ET is monitored, and irrigation adjusted accordingly.

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Effects of deficit irrigation applied to home lawns, used as means of water conservation, are an important issue. However, the impact of deficit irrigation on sucrose metabolism in tall fescue (Festuca arundinacea) is unknown and important because sucrose is the dominant form of carbohydrate transported to developing plant organs. The objectives of this study were to investigate the effects of deficit irrigation on leaf water content, osmotic potential (ψS), sucrose level, and the activity of sucrose phosphate synthase (SPS; EC 2.4.1.14), sucrose synthase (SS; EC 2.4.1.13), and acid invertase (AI; EC 3.2.1.26) in tall fescue leaves. Sods of ‘Falcon II’ tall fescue were established in polyvinylchloride (PVC) tubes (10 cm diameter × 40 cm long) filled with a mixture of sand and fritted clay [9:1 (v:v)] and then placed in growth chambers. Reference evapotranspiration rate [ETo (millimeters of water per day)] was determined by weighing the PVC tubes containing well-watered turfgrass every 3 days to determine water loss on a daily basis as ETo. Deficit irrigation treatments were applied as follows: well-watered control, mild drought stress (60% ETo), and severe drought stress (20% ETo). Leaf water content was lower at 6, 12, and 20 days of treatment for the 20% ETo treatment and 20 days after treatment began for the 60% ETo treatment. Compared with the well-watered control, ψS was lower in the 60% ETo treatment on all three measurement dates. Sucrose was higher at 8 and 14 days after treatment began in the 60% ETo treatment and on all three measurement dates in the 20% ETo treatment relative to the well-watered control. No difference in sucrose level was observed between the 20% ETo and 60% ETo irrigation regimes at 8 and 14 days of treatment. Beginning 14 days after treatment, tall fescue had a higher level of SPS in the 60% ETo and 20% ETo treatments compared with the well-watered treatment. Tall fescue receiving 60% or 20% ETo had a lower level of AI activity on all measurement dates. Results suggest that the decrease in ψS was accompanied by higher sucrose levels, which were the result of the increased level of SPS and SS activity and a decline in AI activity.

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Authors: and

Greenhouse studies were conducted on three warm-season turfgrasses, `Midlawn' bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy], `Prairie' buffalograss [Buchloe dactyloides (Nutt.) Engelm.], and `Meyer' zoysiagrass (Zoysia japonica Steud.), and a cool-season turfgrass, `Mustang' tall fescue (Festuca arundinacea Schreb.) to determine 1) water relations and drought tolerance characteristics by subjecting container-grown grasses to drought and 2) potential relationships between osmotic adjustment (OA) and turf recovery after severe drought. Tall fescue was clipped at 6.3 cm once weekly, whereas warm-season grasses were clipped at 4.5 cm twice weekly. The threshold volumetric soil water content (SWC) at which a sharp decline in leaf water potential (ψL) occurred was higher for tall fescue than for warm-season grasses. Buffalograss exhibited the lowest and tall fescue exhibited the highest reduction in leaf pressure potential (ψP) per unit decline in ψL during dry down. Ranking of grasses for magnitude of OA was buffalograss (0.84 MPa) = zoysiagrass (0.77 MPa) > bermudagrass (0.60 MPa) > tall fescue (0.34 MPa). Grass coverage 2 weeks after irrigation was resumed was correlated positively with magnitude of OA (r = 0.66, P < 0.05).

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Field studies were conducted in south Louisiana to identify plant growth regulators that suppress carpetgrass (Axonopus affinis Chase.) seedhead development. In an initial study, best results were obtained with sethoxydim (0.11 kg·ha-1) and sulfometuron methyl (0.6 kg·ha-1), which reduced seedhead development by 88% and 86%, respectively, compared to untreated plots 21 days after treatment. Sulfometuron methyl caused unacceptable carpetgrass injury, however. Evaluation of seven sethoxydim application levels between 0 and 0.34 kg a.i./ha showed that carpetgrass seedhead number and elongation rate declined with increasing sethoxydim amount [SEEDHEAD NUMBER (m-2) = 515 – 1340 (kg), R 2 = 0.82; ELONGATION (cm) = 25.3 – 151 (kg) + 276 (kg2), R 2 = 0.77]. Carpetgrass seedhead production was restricted up to 6 weeks after sethoxydim (0.17 and 0.22 kg·ha-1) application. Chemical names used: (2-[1-(ethoxyimino)butyl]-5-[2-ethylthio)propyl)-3-hydroxy-2-cyclohexen-1-one) (seth-oxydim); (2-[[[[(4,6-dimethyl-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]benzoic acid) (sulfometuron methyl).

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Authors: and

Establishment of seeded `Zenith' zoysiagrass (Zoysia japonica Steud.) in an existing sward of perennial ryegrass (Lolium perenne L.) is difficult, and chemicals arising from perennial ryegrass leaf and root tissue may contribute to establishment failure. Experiments were done to evaluate zoysiagrass emergence and growth in soil amended with perennial ryegrass leaves or roots, or after irrigation with water in which perennial ryegrass leaves or roots had previously been soaked. Compared to unamended soil, soil amended with perennial ryegrass leaves at 12% and 23% by weight reduced zoysiagrass seedling number 20% and 26%, respectively; root area and mass were reduced 50% when amendments comprised 12% of soil weight. Similar reductions in zoysiagrass seedling emergence and growth were observed in a second soil amendment study, regardless of whether perennial ryegrass was treated with glyphosate or not. Soil mixed with perennial ryegrass leaves, but not roots, at 12% by weight had a high soil conductivity (5.1 dS·m–1), which could have contributed to reduced zoysiagrass emergence and growth. More than 50% fewer zoysiagrass seedlings emerged and root mass was up to 65% lower when irrigated with water in which perennial ryegrass leaves or roots at 5, 10, or 20 g·L–1 were previously soaked for 48 hours. Zoysiagrass leaf area, and root length and area, were also lower when irrigated with water previously containing perennial ryegrass roots. Perennial ryegrass leaves and roots have the capacity to inhibit emergence and growth of `Zenith' zoysiagrass seedlings, which could negatively affect stand establishment.

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Zoysiagrass, in general, has few insect pest problems but may suffer significant damage from infestations of the bluegrass billbug (Sphenophorus parvulus Gyllenhal). This study evaluated ‘Meyer’ and DALZ 0102 zoysiagrass (both Zoysia japonica Steud.) and 31 experimental zoysiagrass progeny, including reciprocal crosses between Z. japonica × Z. matrella (L.) Merr. or crosses between ‘Emerald’ (Z. japonica × Z. pacifica Goudsw.) × Z. japonica. These grasses were evaluated in adjacent experiments with 18 progeny in one and 13 in another. Plots were maintained under golf course fairway conditions and experienced natural infestations of the bluegrass billbug in 2009 and 2010 with larval damage primarily evident in June and continuing throughout the remainder of the growing season. ‘Meyer’ suffered the highest level of damage on each of six rating dates, ranging from 17% to 38% of the experimental plot area affected. Among the zoysiagrass progeny, damage ranged from 0% to 35% with most showing less than 15% damage. Overall, zoysiagrass progeny associated with reciprocal crosses of Z. japonica × Z. matrella or ‘Emerald’ × Z. japonica were less susceptible to bluegrass billbug than ‘Meyer’.

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