Effect of Shade Timing and Intensity on Creeping Bentgrass Influenced By Trinexapac-Ethyl and Plant Protectant.

Turfgrass plant health and growth 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 and has been demonstrated as an effective measurement for quantifying light requirements in various turfgrass systems. The effects of shade timing (morning versus afternoon irradiance) and shade intensity on creeping bentgrass turfgrass quality remain unclear. In addition, the interactions between shade timing, shade level intensity, growth regulators such as Primo Maxx (trinexapac-ethyl) demonstrated to increase creeping bentgrass shade tolerance, and turf colorants/plant protectants such as Turf Screen that promote the ability to increase photosynthetic efficiency need further investigating. The objective of this research is to determine the effects of shade intensity and timing as well as the influence of trinexapac-ethyl and Turf Screen plant protectant on the performance of a creeping bentgrass putting green and to determine the daily light integral requirement to maintain acceptable turfgrass quality. To simulate varying tree shade situations typically found in a golf course setting, this trial applied four different shade intensity treatments (0%, 70%, 80% and 90% reduction of full irradiance) to the turf during morning hours (sunrise to solar noon) or afternoon hours (solar noon to sunset) to observe differences in turf quality. Applications at label rates of trinexapac-ethyl or Turfscreen were made biweekly. Quantum light sensors measuring cumulative photosynthetically active radiation were used to determine daily light integrals for each treatment. Preliminary results indicate that turfgrass quality was significantly reduced under all shade intensities regardless of timing. Turfgrass quality declined more rapidly as shade intensity increased in afternoon shade treatments compared to morning shade treatments. This observation may be explained by average daily light integrals of afternoon shade treatments being lower than morning shade treatments.