Research on nitrate-nitrogen (NO 3 -N) leaching in turfgrass indicates that, in most cases, leaching poses little risk to the environment. Most of the research was conducted on sites that were recently established, and the potential for greater NO 3 -N leaching from mature turf sites is unknown. The fate of nitrogen (N) was examined for a 10-yr-old Kentucky bluegrass (Poa pratensis L.) turf using intact monolith lysimeters and microplots. From October 2000 through July 2002, half of the lysimeters and microplots were treated annually with urea at a high rate of 245 kg N ha 21 (49 kg N ha 21 application 21 ). The remaining lysimeters and microplots were treated annually with urea at a low rate of 98 kg N ha 21 (24.5 kg N ha 21 application 21 ). The Oct. 2000 urea application was made with 15 N double-labeled urea to facilitate fertilizer identification among clippings, verdure, thatch, soil, roots, and leachate. The average total recovery of applied labeled fertilizer nitrogen (LFN) for the low and high N rates was 78 and 74%, respectively. NO 3 -N concentrations in leachate for the low N rate were typically below 5 mg L 21 . For the high N rate, NO 3 -N concentrations in leachate were often greater than 20 mg L 21 . Over approximately 2 yr, 1 and 11% of LFN was recovered in leachate for the low and high N rates, respectively. This research indicates that single dose, high rate, water soluble N applications (49 kg N ha 21 application 21 ) to mature turfgrass stands should be avoided to minimize the potential for NO 3 -N leaching.
Shade is a major cause of poor performance and loss of turf, especially on putting greens. The objectives of this study were to determine the effects of trinexapac‐ethyl (TE) [4‐(cyclopropyl‐alpha‐hydroxymethylene)‐3, 5‐dioxo‐cyclohexanecarboxylic acid ethylester] and nitrogen (N) on the performance and carbohydrate content of creeping bentgrass (Agrostis stolonifera L. cv. ‘Penncross’) grown under reduced light conditions (RLC). The effect of rate and frequency of TE applications to creeping bentgrass under RLC also were evaluated. Two field experiments were conducted during 1998 and 1999 in East Lansing, MI on an established sand‐based putting green mowed to a height of 4 mm. In the first experiment (1998 and 1999), turf grown under 80% black shade cloth received multiple applications of TE (0, 0.042 or 0.070 kg a.i. ha−1) in combination with N (low = 150–185 kg N ha−1 season−1 or high = 212–235 kg N ha−1 season−1). Turf quality and cover were reduced greatly under 80% shade. Application of TE increased turf cover from 6 to 33%, tillers from 40 to 52%, but had no effect on root mass when compared with turf not treated with TE. Fructose content increased by 40 and 37% in turf treated with TE at 0.042 and 0.070 kg a.i. ha−1, respectively. No differences in tissue levels of other carbohydrates or starch were found. Turf cover was 3.3 to 7.2% greater in plots treated with low N when compared with high N. There were no significant interactions between TE and N. In the second experiment (1999), turf grown under 60% green shade cloth received TE (0, 0.025, or 0.050 kg a.i. ha−1) applied on 2‐ or 4‐wk intervals. There were no differences in turf cover in bentgrass grown under 60% shade, regardless of TE treatment. In general, creeping bentgrass quality and color were improved by TE, when compared with untreated turf. Overall, data indicated that TE and judicious use of N can improve creeping bentgrass quality under RLC.
Annual bluegrass (Poa annua L.) may be the most troublesome and studied weed on golf courses in the United States. Given the genetic variability of annual bluegrass and its ability to adapt to different environments, it is important to understand how control methods vary across environments or regions. Our objective was to evaluate seven season‐long regimes of herbicide or growth regulators for annual bluegrass control in creeping bentgrass (Agrostis stolonifera Huds.) putting greens over 3 or 4 years in three states in the midwestern United States. Depending on the product, applications were made as often as every 2 weeks from April through September. Effectiveness of treatments varied widely by location and time, with treatments most effective in Indiana and Nebraska. Paclobutrazol was the most effective plant growth regulator for annual bluegrass control, followed closely by flurprimidol. Intermediate at reducing annual bluegrass was flurprimidol + trinexapac‐ethyl and trinexapac‐ethyl was ineffective. Among herbicides, the now discontinued experimental cumyluron was most effective and four applications of bispyribac‐sodium at 2 oz/acre every 2 weeks in August and September was more effective than 1 oz/acre applied every 2 weeks from May through September or applications of cumyluron. Though a number of products will reduce annual bluegrass on golf greens, overall control was relatively low, reinforcing the need to maximize cultural practices before attempting chemical control. Furthermore, our results reinforce the importance of superintendents’ experimenting and refining treatment regimes in their specific location to maximize efficacy.
Six 1-yr observational studies were conducted from 2001 to 2006 at the Hancock Turfgrass Research Center in East Lansing, MI to characterize the timing, duration, and amplitude of annual bluegrass (AB) (Poa annua L.) seedhead emergence in a 10-to 15-yr-old AB fairway. The objective of this research was to collect data that could be used in the development of a growing degree-day (GDD) model to predict AB seedhead emergence at other locations by using readily available weather station data. New GDD models were compared with previously published models. Plots were established on two adjacent perennial stands of AB maintained at 1.5 cm, receiving 0.5 to 0.6 cm of automatic daily irrigation throughout the growing season and 120 kg N ha -1 yr -1 from 2001 to 2006. The soil type is a Marlette sandy loam (fine-loamy, mixed, semiactive, mesic Oxyaquic Glossudalf). Line intersects and visual estimations of seedhead cover were evaluated multiple times throughout the spring seedhead emergence period. A base temperature of -5 ˚C most accurately predicted the onset, peak duration, and completion of the AB seedhead emergence period for all 5 yr. The final model flowering rate = (-3.331599 × 10 -6 × gdd 2) + (6.968782 × 10-3 × gdd) + -2.841894, accurately predicted (R 2 = .64) flowering stages of an AB fairway turf over 6 yr in Michigan.
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