Arkansas Turfgrass – Mike Richardson, Eric De Boer, and Thomas Walton – University of Arkansas
Last winter (2019-20) was a very mild one for the Natural State. In Fayetteville, our daily high and low temperatures were consistently above the 30-year average and, more importantly, we only had a handful of days when the temperature dropped into the teens and no days where we were in the single digits (Figure 1). However, don’t let one nice, mild winter lull you into thinking that you should not be doing everything you can to prepare for the winter ahead. This is especially true for golf course superintendents that are using warm-season grasses such as ultradwarf bermudagrasses on their greens.
Winterkill has been an ongoing challenge over my 20+ years of doing research in Arkansas and there are still no “magic bullets” or “super grasses” that will solve all of your problems. Although we usually think about those super low temperatures as being the main culprit, winterkill can also be the result of winter desiccation or low-temperature diseases such as spring dead spot. We have conducted countless field trials associated with winterkill at the UofA-Fayetteville over the past twenty years and have investigated everything from cultivars to fertility programs to various winter over-seeding approaches to the use of plant growth regulators (PGRs), wetting agents, fungicides, and protective covers. What have we learned? You should use the best available genetics, apply proper fertility, utilize PGRs, and possibly apply wetting agents, fungicides, and covers!! ALL of the tools in your toolbox should be in play when preparing for the dark days and cold nights of winter. Another factor that is always an issue when winterkill shows up is the overall health of the turf going into the winter. Remember, any area that has been weakened by shade, poor drainage, traffic, compaction, weed competition, herbicide injury, etc., is likely going to be an area that could be damaged by a hard winter.
Genetics are always a great place to start when thinking about avoiding winterkill. The development of cold-tolerant bermudagrass cultivars really ramped up back in the 80s and 90s and was led by the turfgrass breeders at Oklahoma State University, including Dr. Charles Taliaferro and now Dr. Yanqi Wu. Some of their landmark bermudagrass cultivars that have really “moved the needle” in terms of cold tolerance include early vegetative cultivars like Patriot and seeded cultivars like Riviera and Yukon. In recent years, a number of new hybrids such as Latitude 36, Northbridge, and Tahoma 31 have shown even more promise for protection against winterkill. The Arkansas Razorbacks installed ‘Tahoma 31’ bermudagrass in Reynolds Razorback Stadium in 2019 and that selection was primarily based on its superior cold tolerance. The Razorbacks have also converted most of Baum Stadium to ‘Latitude 36’ over the past 5-6 years. Over that time period, issues with winterkill have been almost non-existent with these new grasses. Although more energy has been focused on developing cold-tolerant bermudagrasses than other species, there are also some exciting new developments on the horizon for traditional lawn grasses like St. Augustinegrass.
When looking at the ultradwarf bermudagrasses (UDB) for putting greens, there are fewer options with regards to genetics, but we have certainly seen differences in our trials. We conducted a 3-year trial at Fayetteville that included the major UDB cultivars Champion, MiniVerde, and Tifeagle. Although the degree of winterkill that was observed each year was strongly influenced by the severity of the weather, we consistently saw less winter injury on MiniVerde and Tifeagle than we did on Champion (Figure 2). We recently published that work and would be happy to share a full copy of the paper (De Boer et al., 2019). There are also some new cultivars and experimental lines out there that appear to be promis...