Winter management of ultradwarf bermudagrass putting greens in the transition zone exemplifies the art and science of turfgrass management. Superintendents use the latest research to protect their putting greens from cold temperature injury while also using commonsense strategies to provide the best putting surfaces for golfers in the winter and early spring. Below are several go-to strategies for winter management used by superintendents in the transition zone.
When to Cover to Protect Against Winter Injury
Turf covers help to retain the warmth of the soil and keep soil temperatures warmer than if no covers are used (Booth et al., 2019). This study also found that double covers provided more protection than single covers or single covers with a “dead-air” gap. Tests in freeze chambers show that temperatures between 19 and 23 degrees Fahrenheit result in 50% death of sprigs. However, there is still uncertainly about when ultradwarf putting greens should be covered to protect against low temperature injury. A conservative standard has been to cover when temperatures fall below 25 degrees, but research from the University of Arkansas found that there was no difference in cold temperature injury when their plots were covered at 15, 18, 22 or 25 degrees. The researchers suggest the covering threshold can be reduced below 25 degrees without significant injury to bermudagrass, resulting in reduced labor costs and more hours available for play (DeBoer et al., 2019).
Site-Specific Conditions
The research described above is helpful in designing a program for when to cover greens. However, it is unrealistic to think that there is one “law” that should govern when to use putting green covers. Below are a few examples of site-specific conditions that may warrant the use of a different temperature threshold than the one described above:
North-facing slopes or shaded putting greens – These characteristics are going to keep the soil cooler than it would be on south-facing slopes or putting greens with no shade. It makes sense to be more cautious with these putting greens.
A cold trend is coming – Let’s say you have decided to cover when temperatures are forecast to be 15 degrees or below but the forecast lows for the next three nights are 21, 11 and 14 degrees. It is reasonable to go ahead and cover for these three nights. By covering during the 21-degree night, more warmth is retained in the soil before the colder temperatures arrive.
Early or late frosts – Frosts are an important part of the hardening-off process for a turfgrass plant as it gets ready for winter. However, if an early frost is forecast in the fall and it looks like a warming trend will follow it for a few more weeks, it is reasonable to use the covers to retain color and encourage a little more growth before the winter arrives. In the spring, it is reasonable to use the covers to protect turf that has greened up from a late frost.
Extremely cold temperatures – Double covers work. The question is when to use them. Observations in central Tennessee over the years indicate that it is a good idea to use double covers when temperatures fall to mid-single-digits or lower. If temperatures are forecast below mid-single-digits and you do not have a second cover, using pine straw or leaves may provide additional insulation. Research has been inconclusive with this strategy.
In part two of this series, we will explore the value of implementing a hole location strategy that utilizes three hole locations in each putting green. Stay tuned!
References
Booth, J., J. M. Goatley, D. S. McCall, and S. D. Askew. 2019. Impact of woven polypropylene covering strategies on bermudagrass canopy temperatures. Agron. Abr. 119519.
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, and Turfgrass Management. 5:190019.
Gopinath, L, J.Q. Moss, and Y. Wu. 2021. Quantifying freeze tolerance of hybrid bermudagrasses adapted for golf course putting greens. Hort. Sci. 56(4): 478-480.
Southeast Region Agronomists:
Chris Hartwiger, director, USGA Course Consulting Service – chartwiger@usga.org
Jordan Booth, Ph.D., agronomist – jbooth@usga.org
John Rowland, Ph.D., agronomist – jrowland@usga.org