Forage yield is usually not closely related to CO2 exchange rate of single leaves, and existing data suggest other factors such as canopy characters need to be studied. Therefore, we investigated the relationship between leaf elongation rate and forage yield of 14 genotypes of tall fescue (Festuca arundinacea, Schreb.). Plants were grown in the field under summer water stress and with irrigation. Leaf elongation 4, 8, or 16 days after defoliation was related positively to forage yield at the subsequent harvest during the post‐flowering period. Generally correlations with yield were best (r ≥ 0.67 in 11 of 14 sampling periods) for the 16‐day elongation measurement. Significant differences in leaf elongation at 16 days were noted among genotypes for each of the sampling periods for both irrigated and water‐stressed treatments. Differences among genotypes in leaf elongation were not always consistent from date to date indicating some genotype by environment interaction for this character. Range in leaf length and variance attributable to clones were greater under irrigation which suggested that selection would be more efficient with a good growing environment. Broad‐sense heritabilities for leaf elongation at 16 days calculated for data pooled over 2 years were 0.87 and 0.88 for the water‐stressed and irrigated treatment, respectively. Amount of leaf elongation 12 to 16 days after cutting may be a good estimator of subsequent forage yield because it would indicate the degree of radiation interception during early stages of regrowth, and also the rate of achievement of the critical leaf area index. Leaf elongation rate may be an acceptable criterion for estimating regrowth vigor and yield potential of clones and populations in breeding programs.

The degradation and vertical movement of pendimethalin, chlorpyrifos, isazofos, and metalaxyl were monitored in Kentucky bluegrass (Poapratensis L.) turf managed as a golf course fairway. Intact turf‐soil cores from Mead, NE, on a Sharpsburg soil (fine montmorillonitic, mesic Typic Argiudoll) and Gilbert, IA, on a Nicollet loam (fine‐loamy, mixed, mesic Aqnic Hapludoll) planted to Kentucky bluegrass were periodically removed to 60‐cm depth through 113 d after pesticide application. Cores were sectioned into verdure, thatch, and multiple soil depths. While verdure contained high pesticide concentrations after application, precipitation, and clipping, and degradation reduced the amount in plant tissue with time. Thatch was highly retentive of the pesticides, generally containing the most residue throughout the monitoring period. Pesticide residues tended to be lower in soil at the Iowa site where more thatch was present. Little chlorpyrifos or pendimethalin moved through the thatch to the underlying soil. Isazofos was more mobile and metalaxyl moved through the entire soil column. Soil contained an average of 58% less pesticide than thatch over all sampling times, and concentrations in soil were highest at the 0‐ to 5‐ and 5‐ to 10‐cm depths. Average time for 50% dissipation in the turf‐soil profile (DT50) was 16, 12, 10, and 7 d for metalaxyl, pendimethalin, chlorpyrifos, and isazofos, respectively. The pesticides appeared to degrade more rapidly in the turfgrass environment than typically reported for other agronomic cropping systems. Variability in pesticide residue concentrations for each soil depth among the turf‐soil cores indicated non‐uniform dissipation in the field.

Lowering mowing heights to increase creeping bentgrass (Agrostis palustris Huds.) putting green speed (i.e., ball roll distance) is a common practice. This practice can increase turfgrass susceptibility to heat and drought stress. Other cultural practices might be used to improve putting green quality and speed without additional stress. In this study, vertical mowing was used as a grooming technique to potentially improve putting green quality and speed. A ‘Penncross’ creeping bentgrass turf, established in 1986, was mowed daily at 3.2, 4.0, and 4.8 mm in combination with vertical mowing frequency treatments of 1 and 2 times per month, and a check of no vertical mowing. Mowing height and vertical mowing frequency effects on ball roll distance, turfgrass color and quality, and root production were evaluated in this study during 1989 and 1990. Vertical mowing treatments did not affect ball roll distance, turfgrass color and quality, or root production. Ball roll distance decreased by 0.2 m in 1989 and 0.4 m in 1990 as mowing height increased from 3.2 to 4.8 mm. Relative putting green speeds were rated as fast (i.e., > 2.6 m) across mowing height in 1989, and medium‐fast to fast (i.e. 2.3–2.6 m) in 1990. Turfgrass color, quality, and root production increased with mowing height in 1989 and 1.0 unit in 1990. Turfgrass quality increased by 0.4 rating unit per mm increase in mowing height in 1989 and 1.0 unit in 1990. Root production at two soil depths of 75 to 150 mm and 150 to 225 mm increased with mowing height in 1990.

Visual evaluation parameters are routinely used to assess performance characteristics of turfgrass cultivars in field plantings. Rating systems are commonly employed to evaluate phenotypic variations in color, density, and uniformity of turfgrass stands during the year. In the present study, visual assessment data for quality and density ratings of cultivars of Kentucky bluegrass (Poa pratensis L.) and tall fescue (Festuca arundinacea Schreb.) from 10 turfgrass researchers were statistically analyzed to determine data conformity, consistency, and uniformity. Analysis of simultaneous data gathering by 10 investigators indicated the following: 1) Visual assessment scales were significantly different among evaluators, 2) Visual criteria used for data collection allowed a wide latitude of perception in quality and density characteristics, 3) Relative rank performance of cultivars differed among evaluators, and 4) Presently accepted techniques for visually assessing turfgrass quality and density are inadequate. Results of national and regional turfgrass cultivar evaluation trials should be considered with caution as most performance variables are based on the use of conventional evaluation schemes. This study emphasizes the need for a coordinated development of qualitative evaluation techniques based on substantiated, biologically definable, growth responses rather than visual perception.

Kentucky bluegrass (Poa pratensis L.) has recently been considered for use as turf in high altitude regions of the arid Southwest where saline soils and saline irrigation water are a common problem. A laboratory experiment was conducted using saline hydroponic solutions with seeds of the bluegrass cultivars germinating and growing on floating mats. Solutions made from tap water consisted of 7500, 12 500, and 15 000 ppm NaCl and CaCl2 by weight, on an equal basis. Total germination, days to initial germination, leaf blade length, and blade fresh weight were measured. The objectives of this study were to determine the relative interspecific salt tolerances during germination and seedling growth of 44 bluegrass cultivars. Cultivars had highly significant germination and germination rate responses to salt stress. Seedling growth responses as measured by blade length and blade fresh weight were also significant. We found that a hydroponic growth medium containing 7500 ppm NaCl and CaCl2 salt would be suitable for identifying cultivars that have potential commercial value for saline growing conditions. At this salinity level, cultivars which average less than a 50% reduction in growth parameters relative to top yielding cultivars should be considered. A hydroponic medium with a salt concentration of 12 500 ppm would provide a suitable stress level for screening bluegrass genotypes for improved salt tolerance. Broad‐sense heritability estimates indicate that blade length, germination percentage, and germination rate would be valuable selection criteria for use in screening Kentucky bluegrass cultivars for salt tolerance. Apomictic reproduction may limit genetic improvement from recurrent selection.

Internal heating during sod storage can lead to plant deterioration and is a limiting factor in sod transportation. Storage practices such as the use of refrigeration and vacuum packaging have increased storage time; however, these are usually not practical or economical. Experiments were conducted to develop a feasible growth regulator management technique, using trinexapac-ethyl, to increase the storage life of Kentucky bluegrass (Poa pratensis L.) sod. Experimental setup for all experiments was a completely randomized design with a 2 (trinexapac-ethyl vs. control) × 3 (storage times) factorial treatment arrangement with 3 replications. Trinexapac-ethyl was applied at 0.23 kg·ha-1 to Kentucky bluegrass 2 weeks prior to harvesting. Results showed that sod treated with trinexapac-ethyl was as much as 10 °C cooler than the controls in the center of the sod stacks after 48 hours of storage. The reduced sod temperatures led to a 30% greater tensile strength and 17% better quality ratings in treated sod after 24 hours of storage. A preharvest application of trinexapac-ethyl appears to increase storage times of Kentucky bluegrass sod, which may improve sod market quality. Chemical name used: [4(cyclopropyl-α-hydroxy-methylene)-3,5-dioxocyclohexanecarboxylic acid ethyl ester] (trinexapac-ethyl).

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69.8 W m Ϫ2 (10 Ϫ5 kcal cm Ϫ2 leaf min Ϫ1 ). Other PGRs have also been shown to inhibit respiration. 2,4-D inhib-The plant growth regulators (PGRs) 2,4-D [(2,4-dichlorophenoxy) ited respiration of oat (Avena sativa L.) coleoptiles and acetic acid] and malic hydrazide (1,2-dyhydro-3,6-pyridazinedione) have been shown to reduce plant respiration. The effect of other PGRs pea (Pisum sativum L.) stems at concentrations Ͼ450 such as trinexapac-ethyl [(4-cyclopropyl-␣-hydroxy-methylene)-3,5-M (Kelly and Avery, 1949). French and Beevers (1953) dioxocyclohexanecarboxylic acid methyl ester] on respiration is unshowed a 40% decrease in respiration of corn (Zea mays known. Experiments were conducted to evaluate the effects of tri-L.) mitochondria by 2,4-D at 400 M concentrations. nexapac-ethyl and 2-oxoglutarate on the respiration of mitochondria Switzer (1957) observed nearly a complete inhibition of isolated from wheat (Triticum aestivum 'Arapahoe') seedlings. respiration in soybean [Glycine max (L.) Merr.] mito-Trinexapac-ethyl applied at increasing concentrations inhibited nicochondria by 2,4-D at concentrations of 200 M. Another tinamide adenine dinucleotide (NADH)-dependent O uptake, while PGR, malic hydrazide, has also been shown to inhibit 2-oxoglutarate had no significant effect. This is different than other respiration of isolated soybean mitochondria by 25% at reports that trinexapac-ethyl may compete with 2-oxoglutarate for 20 mM levels (Switzer, 1957). In addition, dinitroaniline binding sites. Different regions of the mitochondria were tested to determine the site of inhibition caused by trinexapac-ethyl. Nicotin-herbicides also have been shown to inhibit mitochonamide adenine dinucleotide dehydrogenase activity, duroquinol-depen-drial O uptake. For example, Trifluralin [2,6-dinitro-N, dent O uptake, and cytochrome bc 1 activity were all reduced by N-dipropyl-4-(trifluoromethyl)benzenamine] inhibited ≈30% in the presence of 10 mM trinexapac-ethyl. Succinate-dependent respiration of mitochondria isolated from sorghum [Sor-O uptake, alternative oxidase, and cytochrome oxidase were not reghum bicolor (L.) Moench], corn, and soybean by Ͼ23% duced by any trinexapac-ethyl concentration. This revealed possible at 400 M concentrations (Negi et al., 1967). Simiinterference of trinexapac-ethyl with ubiquinone binding sites. The lar results were found upon exposing isolated mung reduced form of trinexapac-ethyl was observed to inhibit the electron bean (Vigna radiata L.) mitochondria to other substitransport chain greater than the oxidized form. Reduction in respiratuted 2,6-dinitroaniline herbicides (Moreland et al., tion from trinexapac-ethyl may result in greater stress tolerance in 1972; Moreland and Huber, 1979).treated plants. Hanson (1977) procedure. Seventy-five grams of fresh shoots and Horticulture, Univ. of Nebraska, Lincoln, NE 68583-0724; T.E. were ground using a mortar and pestle and 250 mL of grinding Elthon,