Daily Light Integral Requirement of Creeping Bentgrass Putting Greens Determined By Shade Intensity and Timing.

Turfgrass quality is limited by the availability of photosynthetically active radiation. The cumulative photosynthetically active radiation for one day at a given site is termed the daily light integral (DLI) and has been demonstrated as an effective measurement for quantifying light requirements in various turfgrass systems. However, the minimum daily light integral necessary to produce acceptable quality on a creeping bentgrass (Agrostis stolonifera L.) putting green has yet to be determined. In addition, the impact of shade timing and intensity in combination with the effects of growth regulator Primo Maxx (trinexapac-ethyl) known to increase shade tolerance and turfgrass plant colorant Turf Screen that markets the ability to increase photosynthetic efficiency on daily light integral requirements need further investigating. The objective of this research is to determine the daily light integral requirement of a creeping bentgrass putting green by evaluating the effects of shade intensity and timing and the influence of Primo Maxx and Turf Screen on turfgrass quality in reduced light environments. Four different shade intensity treatments (0%, 70%, 80% and 90% reduction of full irradiance) were applied to the turf during morning hours (sunrise to solar noon) or afternoon hours (solar noon to sunset) to observe differences in turf quality from May through October of 2016. Quantum light sensors measuring cumulative photosynthetically active radiation were used to determine daily light integrals for each treatment. After two years of data collection, the estimated minimum DLI requirement for a 'Tyee' creeping bentgrass green was determined to be 30 mol m^-2 d^-1. While effective in improving turf quality on late summer rating dates, Primo Maxx and Turf Screen did not significantly reduce the minimum DLI requirement of creeping bentgrass.