Covers to increase winter soil temperatures on ultradwarf bermudagrass putting greens

Winterkill of ultradwarf bermudagrass in Fayetteville, Ark., with patterns suggesting enhanced turfgrass survival under seams and air ripples in a protective cover. (Photo: Mike Richardson, Ph.D.)

As ultradwarf bermudagrass (Cynodon dactylon x C. transvaalensis) putting greens move further north in the Transition Zone, there is an increased risk of sustaining low-temperature winter injury. The periodic covering of greens can prevent winter injury.

The benefits of covers for winter protection of putting greens have been well-documented in cool-season and warm-season turfgrasses (3, 4, 5, 6).

In a recent USGA-funded study (1, 2), we determined that reducing the predicted low temperature to cover greens from 25 degrees F to 15 degrees F (-4.0 degrees C to -9.4 degrees C) did not significantly reduce winter survival. However, we observe some winter injury under extremely low temperatures in all covered plots. Our results suggest that the use of industry-standard covers alone may not always be enough to protect greens from winter injury.

There are several cases where winterkill of ultradwarf bermudagrass greens still occurred with a conservative Transition Zone program. On golf courses and in research trials, a consistent observation of winterkill patterns suggests that cover thickness or the presence of air under the covers improves winter survival (Photo 1).

Example batting material treatments before placing the cover. (Photo: Mike Richardson, Ph.D.)

Superintendents have tried various methods to raise covers off the turf canopy and create an air gap, such as placing pine straw, irrigation pipe or even plastic foam “pool noodles” on the green before placing protective covers.

Although the use of materials such as pine straw to create an air gap, in conjunction with covers, has been practiced by superintendents, the effect of an air gap under protective covers on soil temperature has not been tested experimentally on ultradwarf bermudagrass greens in the Transition Zone.

We conducted a preliminary trial during the 2018-2019 winter season at the University of Arkansas Research and Extension Center in Fayetteville, Ark. The trial was on a USGA- constructed green containing large, replicated plots 13 feet by 40 feet (4 meters by 12 meters) of TifEagle ultradwarf bermudagrass.

Cover treatments were applied to the green for low-temperature predictions to fall below 20 degrees F (– 6.7 degrees C). We used a permeable, black woven polypropylene cover (Xton, Florence, Ala.) to cover four of the five plots, with one plot treated as an uncovered control. We used batting in the other three plots (Hendrix Batting, High Point, N.C.). One plot had the Xton cover but no batting (covered control).

Effect of protective covers and batting material weight on spring greenup of TifEagle bermudagrass. Batting weights were 0.75, 1.0 and 1.1 ounces per square foot. (Photo: Eric DeBoer)

A 6-foot by 6-foot (1.8-meter by 1.8-meter) batting piece was installed on plots before placing the cover (Photo 2). Batting weights were 0.75, 1.0 and 1.1 ounces per square foot (229, 305 and 336 g m-2). Data collected in the study included soil temperature at a depth of 2.5 centimeters.

We measured soil temperatures early in the morning (8 to 9 a.m.) or in the afternoon (3 to 4 p.m.). We collected winter survival and greenup data in the spring, but the only significant difference was between the uncovered control and all cover treatments (Photo 3).

The covered control and all batting treatments had significantly warmer soil temperatures on all sampling dates than the uncovered controls (Figure 1). On average, the covered control increased soil temperature 2 to 4 degrees F (1 to 2 degrees C) compared to the uncovered control.

The batting increased the 1-inch (2.5-centimeter) depth soil temperature by 4 to 5 degrees F (2 to 3 degrees C) compared to the cover-only control on most dates. There were no statistical differences in soil temperature under the various batting weight treatments.

Effect of protective covers and various weights of batting fabric on the morning and afternoon soil temperature of an ultradwarf bermudagrass green on two dates in 2019. Different letters within each bar grouping indicate a significant difference.

This preliminary study suggests that an air gap under a protective cover can enhance soil temperature and provide additional protection to warm-season putting greens under extremely low temperatures.

Mike Richardson, Ph.D.; Eric DeBoer; Doug Karcher, Ph.D.; and Thomas Walton, University of Arkansas, Department of Horticulture. Contact Mike Richardson at mricha@uark.edu for more information.

References

1. DeBoer, E. J., M. D. Richardson, J. H. McCalla, and D. E. Karcher. 2019. Reducing ultradwarf bermudagrass putting green winter injury with covers and wetting agents. Crop, Forage & Turfgrass Management 5:190019.

2. DeBoer, Eric, Richardson, Mike Ph.D., and Karcher, Doug, Ph.D. 2017. How low can ultradwarf bermudagrasses go? Golfdom. August 73(8):47.

3. Goatley, J. M. Jr., V. L. Maddox, D. L. Lang, R. E. Elmore, and B. R. Stewart. 2005. Temporary covers maintain fall bermudagrass quality, enhance spring greenup, and increase stem carbohydrate levels. HortScience. 40:227-231.

4. Goatley, J. M. Jr., J. 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. Appl. Turfgrass Sci. p. [1-9].

5. Roberts, J. M. 1986. Influence of protective covers on reducing winter desiccation of turf. Agron. J. 78: 145-147.

6. Shashikumar, K., and J. L. Nus. 1993. Cultivar and winter cover effects on bermudagrass cold acclimation and crown moisture content. Crop Sci. 33:813-817.