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Laurie E. Trenholm and Russell T. Nagata

The objectives of this research were to rank the relative shade tolerance of some new st. augustinegrass (Stenotaphrum secundatum) cultivars and to determine what levels of shade the various cultivars can tolerate. Two consecutive studies were conducted in a glasshouse at the University of Florida Turfgrass Research Envirotron. Cultivars tested were `Bitter Blue', `Floratam', `Palmetto', `Seville', and `1997-6'. Grasses were grown in full sun or under shade structures that provided 30%, 50%, or 70% shade. In trial 1, `Seville' and `1997-6' generally provided best performance under increasing shade, with worst responses seen in `Floratam'. `Seville' and `1997-6' were predicted to maintain an acceptable quality rating of 6 at all shade levels. In trial 2, `Floratam' again had lowest visual quality scores. At 30% shade, `Seville', `Palmetto', and `Bitter Blue' ranked in the highest category, while only `Seville' and `Bitter Blue' had highest rankings at 50% shade. Reduced density was a major factor in turf decline as shade increased. Most of the cultivars performed best under some degree of shade. With the exception of `Floratam', acceptable visual scores were maintained at shade levels exceeding 60% in trial 1 and up to 61% in trial 2.

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Bradley S. Sladek, Gerald M. Henry and Dick L. Auld

, 1999a ). However, a wide range of relative shade tolerance exists between turfgrass species ( Barrios et al., 1986 ; McBee and Holt, 1966 ; Morton et al., 1991 ; Qian and Engelke, 1999a , 1999c ; Qian et al., 1998 ; Tegg and Lane, 2004 ; Winstead

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Jeffrey C. Dunne, W. Casey Reynolds, Grady L. Miller, Consuelo Arellano, Rick L. Brandenburg, A. Schoeman, Fred H. Yelverton and Susana R. Milla-Lewis

trees and/or other structural objects ( Beard, 1973 ) and of the warm-season turfgrasses typically used in the south, bermudagrass exhibits the poorest shade tolerance ( Dudeck and Peacock, 1992 ). The effects of shade can elicit profound physiological

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Laurie E. Trenholm, Lawrence E. Datnoff and Russell T. Nagata

The objectives of these studies were to evaluate the effects of silicon on drought and shade tolerance of st. augustinegrass (Stenotaphrum secundatum). Studies were conducted during 2001 in a glasshouse at the University of Florida Turfgrass Research Envirotron in Gainesville. For both drought and shade evaluations, calcium silicate slag (CaSiO3) was pre-incorporated into pots with commercial potting soil at the rate of 3.36 kg·ha-1 (0.069 lb/1000 ft2). `FX-10' and `FHSA-115' st. augustinegrass were planted into 15.2-cm-diameter × 30.5-cm-deep (6 × 12 inches) plastic pots for the drought study and subjected to minimal irrigation. Under severe drought stress, silicon-amended plants had better responses than non-amended plants. Little improvement was seen under moderate drought stress. `Floratam' and genotype 1997-6 were placed under full sunlight or 50% to 70% shade. There was no benefit from use of silicon under shaded conditions. These findings suggest that silicon might provide improved tolerance to st. augustinegrass under severe drought stress.

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Tara E. Paranick and N. Suzanne Lang

Shaded environments present major obstacles for establishing high quality, persistent, and resistant turfs. Exogenous fructose applications are being examined as a potential method to counteract the effects of shade on turf. This work examines the effectiveness of fructose applications under different light levels on two fine leaf fescue cultivars: chewings fescue (Festucarubra var. commutata) `SR5100' and creeping red fescue (Festucarubra var. rubra) `Dawson'. The experiment was conducted at Michigan State University, East Lansing, inside a simulated dome environment. The experiment was a randomized complete-block design that began 21 Oct. 2004 with two main factors: light and fructose. There were three light treatments: ambient light (shaded); supplemental high light; and supplemental low light. Fructose (0% or 1.25% weight/volume), dissolved in water with an organosilicone adjuvant, was applied once per week. Quality and color ratings, clippings, core samples, density, and leaf reflectance were recorded. In addition, light response curves (LRC) were taken inside an Econoair®

growth chamber using a LI-COR-6400® on the fine fescues, kentucky bluegrass (Poa pratensis) `Cynthia', and bermudagrass (Cyondon dactylon) `Princess'. Preliminary results show that fructose had no significant effect in each light treatment for turf quality and color. However, fructose had a significant impact on clipping weights and density. The LRC specified the required and potential carbon needs as well as indicated the threshold levels, respectively, by species. The impact of fructose alone and in combination with supplemental light on photosynthesis efficiency will be presented.

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Christian M. Baldwin, Haibo Liu, Lambert B. McCarty, Hong Luo and Joe E. Toler

Seasonal variations in temperature and solar radiation in the warm climatic region of the transition zone increase difficulty of creeping bentgrass [Agrostis stolonifera var. palustris (Huds.)] management throughout the year. The impact of winter shade on bentgrass quality and subsequent residual effects of winter shade in spring and summer months has not been investigated. Therefore, a 2-year field study investigated trinexapac-ethyl (TE) [4-(cyclopropyl-α-hydroxy-methylene)-3,5-dioxy-cyclohexanecarboxylic acid ethyl ester] as a winter management strategy to alleviate winter shade stress and determined the winter shade tolerance of ‘L-93’ creeping bentgrass under various reduced light environments. Treatments included a full-sunlight control; 58% and 96% morning, afternoon, and full-day shade artificial; and TE (0.02 kg a.i./ha) applied every 2 weeks from December to July. Data collection included daily light measurements (photosynthetic photon flux density), monthly canopy and soil temperatures, visual turfgrass quality (TQ), chlorophyll concentration, clipping yield, total root biomass, and total root nonstructural carbohydrates. Under 96% shade, canopy temperatures were reduced ≈57% from December to February, whereas soil temperatures were reduced 39% in February compared with full sunlight. Afternoon shade (58%) maintained acceptable TQ throughout winter for both years. Applying TE every 2 weeks in the winter negatively impacted bentgrass quality; however, TE enhanced spring and summer quality. Morning or afternoon shade minimally impacted parameters measured. Overall, moderate winter shade may not limit ‘L-93’ creeping bentgrass performance as a putting green in the transition zone. Results suggest winter shade does not contribute to creeping bentgrass summer decline because all shade-treated plots fully recovered from shade damage in spring months.

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B.G. Wherley, P. Skulkaew, A. Chandra, A.D. Genovesi and M.C. Engelke

., 2002a , 2002b ). Relative to other warm-season species, zoysiagrass possesses good shade tolerance ( Beard, 1973 ; Stier and Gardner, 2008 ) and therefore has developed a niche for use in shady areas of lawns and golf courses where less shade

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Kelly M. Stanton, Sally S. Weeks, Michael N. Dana and Michael V. Mickelbart

, 1977 ). Phenotypic response to light can vary within a species, suggesting that selection may allow for development of cultivars with enhanced shade tolerance ( Kitajima et al., 2006 ; Siemann and Rogers, 2001 ). Spiraea alba and S. tomentosa are

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Ben Wherley, Ambika Chandra, Anthony Genovesi, Mason Kearns, Tim Pepper and Jim Thomas

, 1973 ; Stier and Gardner, 2008 ); however, there is limited published information pertaining to comparative shade tolerance of st. augustinegrass. Trenholm and Nagata (2005) compared performance of five st. augustinegrass cultivars in mild to

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Meghyn Meeks, Ambika Chandra and Ben G. Wherley

Shade tolerance is an important factor for selecting turfgrasses for home lawns and recreational facilities. Beard (1973) estimated that 20% to 25% of established turfgrass stands are impacted by some type of light restriction. Cool-season (C 3