Effect of shade intensity and duration on warm-season turfgrass growth and development

Warm-season turfgrasses, because of their physiology, are less tolerant of lowlight conditions that can be found throughout their range of cultivation. This light reduction can come in the form of seasonal day length variations, seasonal cloud cover, and shade created by plant canopies and other structures. Daily light integral (DLI) is a measurement that takes into account the dynamic nature of shade, and compiles light measurements over a period of 24 hours. Using DLI, many warm-season turfgrasses were evaluated for shade tolerance characteristics and persistence under low light conditions.;Twelve turfgrasses were selected for evaluation to measure DLI requirements to maintain acceptable turfgrass quality (TQ), including over different seasons. Overall, the included bermudagrasses had the highest DLI requirements, with Tifway needing 22.4 mol m-2 d-1 in the summer months. Zoysiagrass and St. Augustinegrass consistently had the lowest DLI requirements, with JaMur zoysiagrass needing 6.7 mol m-2 d -1 to maintain acceptable TQ during the winter.;Shade avoidance and tolerance mechanisms are used by plants to persist under low light conditions. These responses were evaluated in 12 turfgrasses, although no clear indicators were identified to potentially predict these responses to shade. The effect of mowing on DLI requirements under shade was also evaluated for six turfgrasses. Decreases mowing heights increased DLI requirements drastically in some cultivars.;Extended periods of cloud cover can lower irradiance for plants. Various periods of shade duration were evaluated for their effect on five turfgrasses. Only monthly shade consistently reduced TQ in all turfgrasses. Jones Dwarf bermudagrass was the most susceptible to injury, with unacceptable TQ occurring one week after initial shading using 51% shade cloth.;New DLI monitoring instruments are being evaluated for their use in turfgrass applications. The DLI100 daily light meter (DLM) was measured against quantum light sensors (QLS) for accuracy and viability for use in field situations. A linear correlation was observed between the DLM and QLS data, and appears an accurate predictor of DLI in the observed area. Multiple days of measurements should be used with either instrument to improve accuracy.