Abstract
The effectiveness of ethephon for reducing the growth of annual bluegrass (Poa annua L.), when grown as single plants in pot culture in the greenhouse or outdoors, and within a Kentucky bluegrass (Poa pratensis L.) sod, was evaluated. Ethephon reduced the growth of annual bluegrass more than that of Kentucky bluegrass. Concentration was more important in reducing plant spread than the number of applications. Ethephon applied to field grown turf reduced the leaf area per tiller of annual bluegrass but not Kentucky bluegrass. Leaves per tiller and the shoot dry weight of field grown Kentucky bluegrass increased with increasing ethephon rates compared to nontreated plots. Although significant growth retardation occurred for both species in pot culture, only Kentucky bluegrass canopy height decreased in the field with increasing ethephon rates. Decreased Kentucky bluegrass canopy height resulted from reduced sheath length. Chemical names used: (2-chloroethyl) phosphonic acid (ethephon).
Abstract
High temperatures during simulated shipping were more consistently injurious to ‘Merion’ Kentucky bluegrass (Poa pratensis L.) sod than other factors tested. Sod produced with increasing amounts of nitrogen had increased rates of temperature rise. Higher nitrogen levels also increased respiration, percent leaf kill, and ethylene production. There was no consistent effect of 6-benzylamino purine (BA) on sod storage life. Mowing to 2 cm prior to harvest reduced the amount of living tissue, causing lower temperatures, lower respiration rates, and less sod injury. Root production after sod transplanting was greatest from sod grown with 0 and 100 kg/ha of nitrogen fertilization and decreased with higher nitrogen rates.
Efficient utilization of fertilizer-nitrogen (N) by turfgrasses is probably related to N uptake efficiency of roots and metabolic efficiency of absorbed N in roots and shoots. This study evaluated Kentucky bluegrass (Poa pratensis L.) cultivars for potential differences in nitrate uptake rate (NUR), temporal variation in NUR, and the relationship between NUR and N use efficiency (NUE), defined as grams dry matter per gram N. Six cultivars were propagated from tillers of seeded plants, grown in silica sand, mowed weekly, and watered daily with a complete nutrient solution containing 1.0 mm nitrate. A nutrient depletion method from an initial nitrate concentration of 0.5 mm was used to determine NUR of 5-month-old plants. NUR (μmol·h-1 per plant) of the six cultivars ranked as follows: `Blacksburg' > `Conni' > `Dawn' > `Eclipse' = `Barzan' > `Gnome'. When NUR was based on root weight, `Conni' ranked highest; when NUR was based on root length, surface, or volume, `Eclipse' ranked highest. Averaged across cultivars, NUR on the second day was greater than NUR for the first day of nitrate exposure. Temporal variation was greatest in `Blacksburg', while none was noted in `Conni' or `Eclipse'. Cultivar differences in NUE were significant in fibrous roots, rhizomes, and leaf sheaths, but not in leaf blades and thatch. Total nitrate uptake was positively related to total N recovered and total plant dry matter, but NUR based on root weight was negatively correlated with NUE of the whole plant.
Abstract
This study was conducted to determine root distribution, soil moisture depletion, and 32P uptake, as an indicator of water absorption, by Kentucky bluegrass (Poa pratensis L. ‘Fylking’), perennial ryegrass (Lolium perenne L. ‘Manhattan’), and tall fescue (Festuca arundinacea Schreb. ‘Kentucky 31’). 32P was injected at 6, 18, 30, 42, and 54 cm from the soil surface under each turfgrass plot on 18 July 1978. Leaf blade radioactivity revealed differences in uptake among species, but was inconsistent with rooting patterns. Root mass measurements below 36 cm in late August showed tall fescue > perennial ryegrass > Kentucky bluegrass. Root mass above 12 cm showed Kentucky bluegrass > tall fescue = perennial ryegrass. Soil water content (SWC) at three depths in August reflected root distribution for the three species. SWC was lowest under Kentucky bluegrass and highest under tall fescue at 6 cm. At 54 and 78 cm, SWC was highest under Kentucky bluegrass and lowest under tall fescue. SWC was better than 32P injection for detecting species differences in water uptake.
Abstract
Various rates of ethofumesate were evaluated for annual bluegrass (Poa annua L.) control in a perennial ryegrass (Lolium perenne L.) fairway. The tolerance of ‘Merion’, ‘Mystic’, and a blend of Kentucky bluegrasses (Poa pratensis L.) to ethofumesate also was assessed. Ethofumesate at 0.84, 1.1, and 0.84 + 0.84 kg·ha–1 provided poor annual bluegrass control; 2.2 and 1.1 + 1.1 kg·ha–1 provided good control; and 2.2 + 1.1 and 2.2 + 2.2 kg·ha–1 provided excellent control. Overall quality of Kentucky bluegrass was only slightly reduced by ethofumesate at 1.1 or 2.2 kg·ha–1; however, split applications at 2.2 + 1.1 and 2.2 + 2.2 kg·ha–1 severely reduced bluegrass cover and overall quality for 7 months. Foliar growth of sequentially treated Kentucky bluegrass appeared suppressed throughout fall and winter. Between January and April, Kentucky bluegrass plots treated with split applications of 2.2 + 1.1 or 2.2 + 2.2 kg·ha–1 had a dark-green color. No visual injury was observed in perennial ryegrass. Ethofumesate applied at 2.2 or 1.1 + 1.1 kg·ha–1 provided the best combination of safety to Kentucky bluegrass and control of annual bluegrass. Chemical names used: (±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate (ethofumesate).
Abstract
The distribution of photosynthetically fixed carbon within a turfgrass sod was investigated following a routine mowing. The partitioning of 14C-labeled photosynthate was monitored in Kentucky bluegrass (Poa pratensis L. cvs. Baron and Merion) turf 2, 24, and 72 hr after mowing at 3.8 cm. Circles of turf (15 cm in diameter) were exposed to 14CO2 for 15 min, 10-cm-diameter plugs were removed 2 and 24 hr after exposure, and the plants were assayed for radioactivity. Experiments were conducted in late spring, midsummer, and early autumn for 2 years in field plots on a silt loam. Photosynthate translocation from leaf blades to leaf sheaths and crowns was reduced by as much as 25% within 2 hr after mowing but generally returned to a constant and greater rate within 24 hr. Midsummer mowing temporarily inhibited photosynthate transport more than mowing in spring or fall. Photosynthate distribution within turfgrass plants was influenced more by time of year and nutritional status than by mowing. Kentucky bluegrass maintained as closely mowed turf sustains only a slight and temporary disturbance in energy partitioning in response to mowing.
Abstract
A turfgrass blend of ‘Parade’, ‘Adelphi’, ‘Glade’, and ‘Rugby’ Kentucky bluegrasses (Poa pratensis L.) was treated with N-[2,4-dimethyl-5-[[(trifluromethyl) sulfonyl] phenyl] acetamide (mefluidide) at 0.28 and 0.56 kg ha−1; (2-chloroethyl) phosphonic acid (ethephon) at 2.24, 4.48, and 6.72 kg ha−1; 5-(4-chlorophenyl)-3,4,5,9,10-pentaaza-tetracyclo [5,4,1,02,6,08,11]dodeca-3,9-diene (BAS 106 00 W) at 1.68, 3.36, and 5.04 kg ha−1, and α-(1-methylethyl)-α-[4-(trifluromethoxy) phenyl]-5-pyrimidinemethanol (EL-500) at 0.84, 1.21, and 1.40 kg ha−1 in field and greenhouse studies. Each of the materials investigated was effective in retarding Kentucky bluegrass growth in field studies. However, effects on growth inhibition and turfgrass quality varied between years. Ethephon was the only material not effective in reducing clipping yield in the greenhouse, whereas none of the growth retardants inhibited root organic matter production or rhizome weight in the greenhouse study.
Abstract
Germination responses of creeping bentgrass (Agrostis palustris Huds.) and Kentucky bluegrass (Poa pratensis L.), and annual bluegrass (Poa annua L.) to elevated temperature were evaluated by germinating seed in sustained temperature regimes or by moving imbibed seed from high to intermediate or from intermediate to high temperatures. ‘Penncross’ creeping bentgrass germinated well at 40°/30°C (day/night) temperature or when moved from 40/30° to 25°/18° or from 25°/18° to 40°/30°. ‘Baron’ Kentucky bluegrass seed germination was decreased by 34°/28° and there was no germination at 40°/30°. Moving imbibed seed from 40°/30° to 24°/18° resulted in a high germination percentage, while imbibition for 12 or 24 hours at 25° resulted in some germination at 40°/30°. Annual bluegrass seed germination was significantly less at 34°/28° than at 25°/18° and was prevented at 40°/30°. Imbibition at 40°/30° prior to 25°/18° decreased germination and there was no annual bluegrass germination at 40°/30° regardlessf of pretreatments at 25° for up to 24 hours.
Abscisic acid (ABA) and glycine betaine (GB) may regulate plant responses to drought or salinity stress. The objectives of this controlled-environment study were to determine whether foliar application of ABA or GB improves turf quality under drought or salinity and whether improved stress responses were associated changes in antioxidant metabolism in two C3 turfgrass species, creeping bentgrass (Agrostis stolonifera) and kentucky bluegrass (Poa pratensis). Physiological parameters evaluated included turf quality, leaf relative water content, membrane electrolyte leakage (EL), membrane lipid peroxidation [expressed as malondialdehyde (MDA) content], and activity of superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX). Abscisic acid and GB were both effective in mitigating physiological damage resulting from drought or salinity for both grass species, but effects were more pronounced on kentucky bluegrass. The most notable effects of ABA or GB application were the suppression of EL and MDA accumulation and an increase in APX, POD, and SOD activities after prolonged periods of drought (21 days) or salinity stress (35 days). These results suggest foliar application of ABA or GB may alleviate physiological damage by drought or salinity stress in turfgrass and the maintenance of membrane stability and active antioxidant metabolism could contribute to the positive effects in the stress mitigation effects.
Carbohydrate metabolism is important for plant adaptation to drought stress. The objective of this study was to examine major forms of carbohydrates associated with superior drought tolerance and post-drought recovery in kentucky bluegrass (Poa pratensis) by comparing responses of different forms of carbohydrates with drought stress and re-watering in two cultivars contrasting in drought tolerance. Plants of drought-tolerant ‘Midnight’ and drought-sensitive ‘Brilliant’ were maintained well watered or subjected to drought stress for 10 days by withholding irrigation, and drought-stressed plants were re-watered for 3 days. Physiological analysis (turf quality, relative water content, and electrolyte leakage) confirmed the genetic variability of the two cultivars in drought tolerance. The two cultivars exhibited differential responses to drought stress and re-watering for the content of water-soluble sugars (sucrose, fructose, and glucose) and storage carbohydrates (starch and fructan), and ‘Midnight’ maintained higher sucrose content at 10 days of drought stress and more fructan at 3 days of re-watering. The greater accumulation of sucrose in ‘Midnight’ under drought stress corresponded with higher activities of two sucrose-synthesizing enzymes (sucrose phosphate synthase and sucrose synthase) but was not related to the sucrose-degrading enzyme activity (acid invertase). These results suggested that increased sucrose accumulation resulting from the maintenance of active sucrose synthesis could be associated with superior turf performance during drought stress, whereas increased fructan accumulation could contribute to rapid re-growth and post-drought recovery on re-watering in kentucky bluegrass.