In the Northern Hemisphere at this time of year, winter weather is behind us, and spring green-up season is upon us. Bermudagrass putting greens today have the desired quality, density and mowing tolerance at 1⁄8th-inch (≤ 3 millimeters) height-of-cut,
but from a plant physiology point of view, there could be a reduction in freezing tolerance. This means those bermudagrasses are perhaps more susceptible to winter injury or winterkill.
During the winter, turf covers have become a valuable and often-relied-upon tool to favorably influence turfgrass canopy and root-zone temperatures, turfgrass crown and soil hydration properties, and even turfgrass establishment from seed or stolons.
Turf covers “act” in the same way as clouds in the sky.
I recall a book from my graduate school climatology class (“Clouds in a Glass of Beer: Simple Experiments in Atmospheric Physics” by C.F. Bohren). Basically, clouds modify the intensity of solar radiation (i.e., sunlight) passing through the
cloud cover to reach the earth’s surface, and then the clouds trap that radiant solar energy trying to escape back into the atmosphere. The use of turf covers for bermudagrass putting greens goes back to a 1929 USGA Green Section report of pine
straw cover commonly employed for winter protection.
For those managing bermudagrass putting greens in the transition zone and mid-south regions of the U.S., let’s revisit research conducted on winter turf covers. Researchers at Mississippi State University (Starkville, Miss.) evaluated several different
covers on a bermudagrass putting green (Cynondon magenissii MS-Express) for their ability to modify surface air temperature and for their influence on photosynthetically active radiation (PAR).
Incidentally, PAR is that portion of the sunlight spectrum utilized by plants for photosynthesis.
About 50% of total sunlight is PAR (i.e., 400-700 nanometer wavelength); however, about 1% to 2% of that total sunlight is absorbed by plants for photosynthesis.
The study was conducted over three consecutive winter seasons on the same practice putting green. Test plots were about 10 feet × 10 feet (3 meters × 3 meters) with three replications per treatment (i.e., 12 turf covers and a no-cover treatment).
The covers were applied when the minimum air temperature was predicted to be ≤ 25 F (minus 4 C) for two consecutive days and were secured in place with sod staples. Those bermudagrass plots were not covered the entire winter, but only during those
severe low air temperature periods to mimic temporarily closing greens for play. Data logger devices were installed under each cover in each plot to record surface air temperature at 15-minute intervals, and a photometer was used to measure surface
PAR for all plots.
Three winter seasons of data were compiled and revealed that two white covers and one clear cover had 34% to 49% reduction in PAR; three black covers and two experimental covers had ≥ 87% reduction in PAR; and four standard or commonly used covers
had 64% to 79% reduction in PAR. Keep in mind, covers that severely restrict PAR may cause a delay with bermudagrass spring green-up. All covers provided higher surface temperatures for those plots versus the uncovered plots. Overall, surface temperature
responses varied with cover material composition, permeability, color, layering and thickness.
So, for those managing bermudagrass putting greens in regions with cold winters, a good “rule-of-thumb” recommendation would be to cover those greens if air temperatures are forecast to be ≤ 25 F. This study demonstrated that all covers
evaluated provided some useful amount of surface temperature modification and severe cold weather protection for a bermudagrass putting green, but the cover selected would depend on the particular needs of the golf course. The type of covering material
is not as critical for winter weather protection, and therefore a lightweight, durable material that is easy to install and remove should help to minimize labor and resources.
And, the golfers will certainly appreciate the excellent playing surface conditions in the spring when bermudagrass starts to green up.
Source: Goatley, J.M., P. Sneed, V.L. Maddox, B.R. Stewart, D.W. Wells and H.W. Philley. 2007. Turf covers for winter protection of bermudagrass golf greens. Applied Turfgrass Science 4(1):1-10 (https://doi.org/10.1094/ATS-2007-0423-01-RS).
Mike Fidanza, Ph.D., is a professor of plant and soil science in the Division of Science, Berks Campus, at Pennsylvania State University in Reading, Pa. He is a 21-year member of GCSAA.