Impact of turf fans on creeping bentgrass greens

The physiology of creeping bentgrass [Agrostis stolonifera L. var palustris (Huds.)] is negatively impacted during periods of stress, decreasing the efficiency of many vital functions. Optimal creeping bentgrass growth occurs between 50 and 64 degrees. Root development slows as the soil temperature rises above 80, with a loss of functionality at soil temperatures above 86.

To mitigate environmental stresses to creeping bentgrass, turf fans are used on many golf courses to improve airflow and increase transpiration. The objectives of this research were to 1) spatially quantify benefits of turf fans on the overall health of creeping bentgrass putting greens and 2) determine optimal activation timing to maximize creeping bentgrass performance during summer stress.

Each main plot consisted of an entire green with a unique fan application (no fan, activate fan at 70 degrees soil temperature, and activate fan at 80 degrees soil temperature). Six in-play creeping bentgrass (Penn A1/A4) greens were equipped with permanent 5 horsepower oscillating turf fans (TurfBreeze TB-50 Premium, 45,000 CFM) and compared against three comparable greens without fans.

The study was repeated once, with data collection in 2013 and 2014. Fans were activated when daily soil temperature at 1.5 inches averaged 70 degrees and 80 degrees. Once activated, each fan ran continuously throughout all data collections.

Root depth, root zone temperature and canopy temperatures were positively impacted by fans, regardless of activation date, and were strongly correlated to surface wind speed. Surface wind speeds of 9 mph can reduce soil temperatures by 4 degrees. Impact was most apparent for the first 40 feet from the fans. Surface airflow ranged from 12 mph (20 feet) to 3.6 mph (70 feet), compared to 2 mph on greens with no fans.

Root zone temperature was negatively correlated with two vegetation indices (NDVI and RVI), which are used as objective measurements of reflectance to quantify turf health. Using this correlation, reflectance maps were generated to predict root zone temperatures across entire greens. Duration between fan activation dates was 18 days in 2013 and 36 days in 2014. Late-season rooting depth were slightly longer when fans were activated early, suggesting creeping bentgrass may benefit from extra air movement prior to peak summer stress.

David McCall and Erik Ervin, Ph.D. are at Virginia Tech University and Dana Sullivan is at TurfScout, LLC., Greensboro, N.C.