SportsTurf

www.stma.org May 2016 | SportsTurf 9 Conversely red light (~ 600 – 700 nm) is also important for photosynthesis, and is the stimulus for turfgrass cell elongation. Green light typically is not important for photosynthesis and is refl ected giving the turf its green color. Light quantity is the actual particles of light providing the energy necessary for photosynthesis to occur. Light quantity (energy) is the most important light component for photosynthesis to occur. Variations in light quantity occur with the time of year, latitude, time of day, atmospheric screening, structures (stadiums, fences, etc.), and topography. During the summer light quantity is greatest; while, winter provides the least light energy. Many sports are played in spring and fall, and even into the winter months where light quantity for turfgrass growth may be limited. Depending on the time of year and latitude, the light quantity can vary greatly. In the northern hemisphere the farther north you go during the summer the longer the days are and greater the light quantity. Between 12:00 and 14:00 the light energy is most abundant. It is signifi cantly less abundant during the time of day before and after the time when the sun is at it solar zenith. Atmospheric screening reduces light quantity, and is caused by anything that has a potential to interfere with the light wavelengths. Clouds, air pollution, humidity, and even stadiums and fences are some examples of atmospheric screening that can limit growth on athletic fi elds. Dr. James Beard (1995) estimated that over 25% of all managed turf is under some sort of shade stress. Thus, shade stress likely occurs anywhere turfgrass is managed which can include golf courses, athletic fi elds, and home lawns to name a few. Shade (reduced light) is a reduction in both light quantity and quality. Simply having a shade situation means not enough light energy is being supplied to the turf for effi cient photosynthesis to occur. Reduced photosynthesis results in reduced carbohydrate synthesis, and in turn causes turfgrass stress conditions resulting in insuffi cient growth and development. Tree shade greatly reduces both blue and red light quality, with the blue light being affected the greatest. As a result the short sturdy stimulus for turfgrass growth is reduced and turfgrasses elongate from the more abundant red light stimulus, and continue to lack the necessary light energy important for optimal photosynthesis to occur. Morphological changes that occur as a result of shade stress include decreased leaf thickness, decreased density, decreased tillering (rhizome and/or stolon growth), decreased root to shoot ratio, and increased leaf height and elongation. Turfgrass physiological responses to shade include reduced car- bohydrate reserves, reduced transpiration, reduced respiration, reduced cuticle thickness, and increased succulence. As a result of these morphological and physiological changes, athletic fi elds have a decreased capacity to recover from traffi c damage. Environmental conditions that typically accompany shade stress situations include increased relative humidity, more moderated temperatures, and restricted air movement. In turn, athletic fi elds become more susceptible to common low light turfgrass diseases like pink snow mold and powdery mildew. Proper implementation of cultural practices can help when managing sports fi elds under shade stress conditions. Because root depth is limited as a result of shade a light and more frequent irrigation schedule should be used. However, avoid over watering! Irrigate only as needed to maintain adequate soil moisture for the turfgrass. Also, avoid excess nitrogen. Too much nitrogen will stimulate increased shoot growth; thus, making the turfgrass plant more stressed. A good rule of thumb to go by is to fertilize at half the recommended rate for nitrogen requirements for the turfgrass species being grown. If possible increase mowing height to enable more surface area for light absorption. Unfortunately, for a shaded putting green increasing the mowing height is often not possible, because of the increased demands for faster putting surfaces. Finally, turfgrasses under shade stress conditions have an increased susceptibility to fungal turfgrass diseases. Therefore, if possible fungicide applications are often necessary for turfgrass survival. Other management practices aid in turfgrass shade stress situations include limiting or redirecting traffi c, tree canopy and root pruning, using plant growth regulators and increasing morning light. Although limiting traffi c may be diffi cult, particularly on putting greens. However, any reduction in wear Stadium grow lights at Lambeau Field, Green Bay, WI. and quality. Simply having a shade situation means not enough light energy is being supplied to the Reduced photosynthesis results in reduced growth is reduced and turfgrasses elongate from the more abundant red light stimulus, and continue to lack the necessary light energy important for optimal photosynthesis to occur. Morphological changes that occur as a result of moisture for the turfgrass. Also, avoid excess nitrogen. Too much nitrogen will stimulate increased shoot growth; thus, making the turfgrass plant more stressed. A good rule of thumb to go by is to fertilize at half the recommended rate for nitrogen requirements for the turfgrass the mowing height is often not possible, because of the increased demands for faster putting surfaces. Finally, turfgrasses under shade stress conditions have an increased susceptibility to fungal turfgrass diseases. Therefore, if possible fungicide applications are often 25% of all managed turf is under some sort of shade stress PHOTO COURTESY OF SIMON GUMBRILL OF STADIUM GROW LIGHTING.

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