Temporal shade on creeping bentgrass turf

Creeping bentgrass (Agrostis palustris Huds.) turf exposed to shade during morning hours map decline more readily than similar turf exposed to afternoon shade. This study compared the quality and physiological responses of creeping bentgrass turf exposed to morning shade with turf exposed to afternoon shade and evaluated responses of the same species exposed to varying shade densities during the same period. Semipermanent shade structures were placed on a creeping bentgrass range maintained at a 6.4-mm height. Structures provided 6 h of morning shade or 6 h of afternoon shade during the summer solstice. Each structure was covered with either 80 or 100% shade cloth and replicated three times. Control treatments of full sun and perpetual shade were also included. Treated turf was evaluated monthly for color, density, root mass, pigment concentrations, and total nonstructural carbohydrates (TNC). Regardless of response tested, no significant variation was found between plots receiving morning shade and afternoon shade or between plots in 80 and 100% shade. Canopy temperature, in comparison with air temperature, was 7% greater in morning shade than in afternoon shade, but the relation ship between canopy temperatures in full sun and shade did not change during the day. Perpetual shade caused a 38% decrease in color and a 33% decline in density but treatments receiving 6 h of shade did not vary from the full sun treatment. Concentrations of chlorophyll a (46%) and b (50%), neoxanthin (31%), violaxanthin (44%), and lutein (34%) declined in perpetual shade compared with full sun. Violaxanthin concentration was influenced by photosynthetic photon flux, suggesting its potential use as a shade stress indicator.