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D.S. Glinski, H.A. Mills, K.J. Karnok, and R.N. Carrow

Root growth of `Penncross' creeping bentgrass (Agrostis palustris Huds.) plugs sodded into a sandy loam soil and fertilized with five 1:1, 1:3, and 0:1) were evaluated. Root growth and root: shoot ratios were higher with as the predominant N form. Results from this study indicate should be the predominant N form when rapid and extensive root development is desired for the establishment of sodded bentgrass.

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Sang Ryul Shim and B.J. Johnson

Creeping bentgrass (Agrostis palustris Huds.) putting greens are commonly infested with crabgrass (Digitaria spp.) and goosegrass [Eleusine india (L.) Gaertn.]; however, many herbicides have the potential to severely injure this turfgrass species. A field investigation was conducted over 2 years to determine the tolerance of creeping bentgrass to various herbicides. Trifluralin plus benefin (2.2 to 6.7 kg·ha-1), dithiopyr (0.37 to 1.1 kg·ha-1), and prodiamine (0.5 to 1.7 kg·ha-1) did not injure creeping bentgrass. Pendimethalin caused only slight injury when applied at 3.4 kg·ha-1, but injury increased in 1 of 2 years when applied at ≥6.7 kg·ha-1. Creeping bentgrass was severely injured when treated with benefin plus oryzalin (≥4.5 kg·ha-1), fenoxaprop (0.07 kg·ha-1), and oxadiazon (3.4 kg·ha-1) granular and WP formulations and, therefore, should not be applied to the turf. Chemical names used: N -butyl-N -ethyl-2, 6-dinitro-4-(trifluoromethyl) benzenamine (benefin); S,S -dimethyl 2-(difluoromethyl-4-(2-methylpropyl)-6-(trifluoromethyl-3, 5-pyridinedicarbothioate (dithiopyr); (±) 2-[4-[(6-chloro-2-benzoxazolyl)oxy]phenoxy]propanoic acid (fenoxaprop); 4-(dipropylamino)-3,5-dinitrobenzenesulfonamide (oryzalin); 3-[2,4-dichloro-5-(l-methylethoxy)phenyl]-5-(1,1-dimethylethyl)-1,3,4-oxadiazol-2-(3H)-one (oxadiazon); N -(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine (pendimethalin); 2,4-dinitro N,N -dipropyl-6-(trifluoromethyl)-1,3-benzenediamine (prodiamine); 2,6-dinitro-N-N -dipropyl-4-(trifluoromethyl)benzenamine (trifluralin).

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J.L. Nus and M.A. Sandburg

Throughout the north-south climatic transition zone of the eastern United States, cool- and warm-season turfgrasses are used adjacently. A greenhouse study with creeping bentgrass (Agrostis palustris Huds.) was initiated to determine threshold concentrations of atrazine, an effective pre- and postemergence herbicide for warm-season turfgrasses, that would result in unacceptable levels of phytotoxicity to seedling and mature creeping bentgrass. Mature and 8-week-old seedling `Penncross' creeping bentgrass were given 6.5 mm of daily irrigation of untreated water or water containing atrazine at 0.01, 0.02, 0.04, 0.08, 0.16, 0.32, 0.64, 1.28, or 2.56 mg·liter-1. A model of quality ratings taken 20 days after the initiation of treatments indicated threshold concentrations resulting in unacceptable turf quality to be approximately 0.05 and 0.08 mg·liter-1 for seedling and mature bentgrass, respectively. Chemical name used: 2-chloro-4-ethylamino-5-isopropylamino-s-triazine (atrazine).

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Charles F. Mancino and Joseph Troll

Combining frequent N applications and irrigations for turfgrasses grown in sandy soils is a common occurrence on golf course putting greens. A greenhouse study was conducted to determine leaching losses of nitrate and ammonium nitrogen from `Penncross' creeping bentgrass (Agrostis palustris L.) growing on an 80 sand:20 peat soil mixture following frequent, moderately heavy irrigations and light or moderate N fertilizer applications. Nitrogen sources included calcium nitrate, ammonium nitrate, ammonium sulfate, urea, urea formaldehyde and isobutylediene diurea. Application levels were 9.76 kg N/ha per 7 days and 19.52 kg N/ha per 14 days for 10 weeks. Irrigation equivalent to 38 mm·week-1 was applied in three equal applications. Overall, 46% of the applied water leached. Total leaching losses were <0.5% of the applied N. Nitrate represented the major portion of the leached N, with ammonium losses being negligible. There were no differences between sources when applied at these levels. In a second study, a single 48.8 kg N/ha application resulted in higher leaching losses of N, but only calcium nitrate and ammonium nitrate had total losses > 2% (2.80% and 4.13%, respectively, over an n-day period). Nitrate concentrations were found to exceed 45 mg·liter-1 for ammonium nitrate.

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Xiaozhong Liu and Bingru Huang

Summer decline in turf quality of creeping bentgrass (Agrostis palustris Hud.) is a major problem in golf course green management. The objective of this study was to examine whether seasonal changes and cultivar variations in turf performance are associated with changes in photosynthesis and respiration rates for creeping bentgrass. The study was conducted on a USGA-specification putting green in Manhattan, Kans., during 1997 and 1998. Four creeping bentgrass cultivars, `L-93', `Crenshaw', `Penncross', and `Providence', were examined. Grasses were mowed daily at 4 mm and irrigated on alternate days to replace 100% of daily water loss. In both years, turf quality, canopy net photosynthetic rate (Pn), and leaf photochemical efficiency (Fv/Fm) were high in May and June and decreased to the lowest levels in July through September. Whole-plant respiration rate (R) and canopy minus air temperature (▵T) increased during summer months. In October, turf quality and Pn increased, whereas R and T decreased. During summer months, turf quality was highest for `L-93', lowest for `Penncross', and intermediate for `Providence' and `Crenshaw'. Seasonal changes and cultivar variations in turf quality were associated with the decreasing photosynthetic rate and increasing respiration rate.

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Xiaozhong Liu and Bingru Huang

Low mowing increases ball roll distance on putting greens, but may affect growth and physiological responses to summer heat stress. The objective of this study was to examine whether the effect of mowing heights on turf summer performance was associated with changes in photosynthetic activities and respiration rate for two creeping bentgrass [Agrostis palustris (L.) Huds] cultivars, `Crenshaw' and `Penncross'. Both cultivars were grown under USGA-specification putting green conditions from 1997 to 1998. Grasses were mowed daily at a 3-mm (low mowing) or 4-mm (high mowing) height. Turf quality, net photosynthesis rate (Pn), and leaf photochemical efficiency (Fv/Fm) declined, whereas respiration rate of whole plants, canopy minus air temperature, and soil temperatures increased under low mowing compared to those at the high mowing height. The decline or increase in those parameters under low mowing was more pronounced in summer than in spring or fall months. The results showed that turf quality was better at the 4-mm mowing height, especially during summer months. Better quality at the higher mowing height could be related to the maintenance of higher photosynthetic activities and lower respiration rate. Mowing at the lower height had more adverse effects on turf growth and photosynthetic capacity for `Penncross' than `Crenshaw', particularly during summer months.

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Xiaozhong Liu and Bingru Huang

Previous studies found that high soil temperature is more detrimental than high air temperature for the growth of creeping bentgrass (Agrostis palustris L.). The objective of the study was to investigate changes in fatty acid composition and saturation levels in leaves and roots for creeping bentgrass exposed to high soil temperature. Shoots and roots of `Penncross' plants were subjected to a differential air/soil temperature of 20/35 °C in a growth chamber. Soil temperature was controlled at 35 °C using an immersion circulating heater in water bath. Shoot injury induced by high soil temperature was evaluated by measuring level of lipid peroxidation expressed as malonyldialdehyde (MDA) content, chlorophyll content, and photochemical efficiency (Fv/Fm) of leaves. MDA content increased while chlorophyll content and Fv/Fm decreased at high soil temperature. The content of total fatty acids and different species of fatty acids were analyzed in both leaves and roots. Total fatty acid content in leaves increased initially at 5 days of high soil temperature and then decreased at 15 days, while total fatty acid content in roots decreased, beginning at 5 days. Linolenic acid was the major fatty acid in leaves and linoleic acid and palmitic acid were the major fatty acids in roots of creeping bentgrass. Leaf content of all fatty acid components except oleic acid increased initially and then decreased at high soil temperature. Root content of all fatty acid components except palmitoleic acid and oleic acid decreased, beginning at 5 d of high soil temperature. Oleic acid in leaves and palmitoleic and oleic acid in roots did not change during the entire experimental period. Leaf content of saturated fatty acids and unsaturated fatty acids increased during the first 5 to 10 days of high soil temperature and decreased at 15 and 25 days, respectively. Root content of saturated fatty acids and unsaturated fatty acids decreased beginning at 5 days of high soil temperature. Double bond index decreased in both leaves and roots. High soil temperature induced changes in fatty acid composition and saturation levels in leaves and roots, and this could be associated with physiological damages in leaves even though only roots were exposed to high temperature.

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Yali He, Xiaozhong Liu, and Bingru Huang

The acclimation of plants to moderately high temperature plays an important role in inducing plant tolerance to subsequent lethal high temperatures. This study was performed to investigate the effects of heat acclimation and sudden heat stress on protein synthesis and degradation in creeping bentgrass (Agrostis palustris Huds.). Plants of the cultivar Penncross were subjected to two temperature regimes in growth chambers: 1) heat acclimation—plants were exposed to a gradual increase in temperatures from 20 to 25, 30, and 35 °C for 7 days at each temperature level before being exposed to 40 °C for 28 days; and 2) sudden heat stress (nonacclimation)—plants were directly exposed to 40 °C for 28 days from 20 °C without acclimation through the gradual increase in temperatures. Heat acclimation increased plant tolerance to subsequent heat stress, as demonstrated by lower electrolyte leakage (relative EL) in leaves of heat-acclimated plants compared to nonacclimated plants at 40 °C. Heat acclimation induced expression of some heat shock proteins (HSPs), 57 and 54 kDa, detected in a salt-soluble form (cystoplasmic proteins), which were not present in unacclimated plants under heat stress. However, HSPs of 23, 36, and 66 kDa were induced by both sudden and gradual exposure to heat stress. In general, total protein content decreased under both heat acclimation and sudden heat stress. Cystoplasmic proteins was more sensitive to increasing temperatures, with a significant decline initiated at 25 °C, while sodium dodecyl sulphate (SDS)-soluble (membrane) protein content did not decrease significantly until temperature was elevated to 30 °C. The results demonstrated that both a gradual increase in temperature and sudden heat stress caused protein degradation and also induced expression of newly synthesized HSPs. Our results suggested that the induction of new HSPs during heat acclimation might be associated with the enhanced thermotolerance of creeping bentgrass, although direct correlation of these two factors is yet to be determined. This study also indicated that protein degradation could be associated with heat injury during either gradual increases in temperature or sudden heat stress.

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Mark J. Carroll and A. Martin Petrovic

Nitrogen (96 and 192 kg·ha-1·year-1) and K (0, 48, 96, and 192 kg·ha-1·year-1) were applied in factorial combination over 4 years to two creeping bentgrass (Agrostis palustris Huds.) and one Kentucky bluegrass (Poa pratensis L.) field plot locations. Turfgrass wear tolerance and recovery from wear were evaluated in the 3rd and 4th years of N and K application by visually estimating the percentage of unworn turf present at the wheel track of a wear simulator or by determining the fresh weight of turfgrass tissue collected from cores removed within, and outside the simulator wheel track. Increasing the supply of N improved creeping bentgrass wear tolerance in the 4th year, but had no effect on Kentucky bluegrass wear tolerance. Nitrogen did not influence recovery from the wear of either species over 8 to 14 days of evaluation following the imposition of wear. Potassium did not affect the wear tolerance or recovery from wear injury in either species.

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J.D. Fry, P.H. Dernoeden, W.S. Upham, and Y.L. Qian

Field studies were conducted in Kansas and Maryland to compare the safety and efficacy of halosulfuron-methyl (HM) and bentazon for topkill of yellow nutsedge (Cyperus esculentus L.). Kentucky bluegrass (Poa pratensis L.) and creeping bentgrass (Agrostis palustris Huds.) treated with single (in Kansas) or sequential (in Maryland) HM (35 to 140 g·ha–1) or bentazon (1120 or 1680 g·ha–1) applications exhibited little injury, and treated turf had acceptable quality in all studies. Bentazon caused an unacceptable reduction in perennial ryegrass (Lolium perenne L.) quality at ≥5 weeks after treatment in four of five tests. Perennial ryegrass quality declined linearly with increasing HM rates (between 35 and 140 g·ha–1). In Maryland, HM (≥70 g·ha–1) elicited unacceptable perennial ryegrass quality for 2 or 3 weeks; however, in Kansas, quality was unacceptable for ≈1 week. In Kansas, yellow nutsedge topkill by HM (70 kg·ha–1) ranged from 52% to 97%. A single HM application (35, 70, or 140 kg·ha–1) provided > 97% topkill in Maryland. Yellow nutsedge topkill by bentazon (1680 g·ha–1) generally was inferior to that by HM (70 g·ha–1). Chemical names used: 3-(1-methylethyl)-1H-2,1,3-benzothiadiazin-4 (3H)-one 2,2-dioxide (bentazon), methyl 3-chloro-5-(4,6-dimethoxypyrimidin-2-ylcarbamoylsulfamoyl)-1-methylpyrazole-4-carboxylate (halosulfuron-methyl).