ROOTED INRESEARCH BERMUDAGRASS WINTER SURVIVAL—
By Cale A. Bigelow, PhD
After a lack of snow and a “warmer than normal” winter, Mother Nature gave the Midwest a wave of “False Spring,” with fluctuating warm and cold temperatures that included early morning freezes in early April. While this holds back summer annual establishment, it also delays the green- up of warm-season grasses like bermudagrass. Since we see increasing adoption of the cold hardy bermudagrass cultivars throughout the region for turfgrass areas such as athletic fields, here I try to answer some industry questions regarding bermudagrass management and how/if the degree of winter hardiness may affect winter survival. I dug back into the research journal reports regarding bermudagrass grow-in and maintenance nutritional projects, with an emphasis on nitrogen (N), and how N management may affect winter survival.
Te fundamental question: “Does N nutrition affect winter hardiness?”
For anyone planting and maintaining bermudagrass— winter hardiness is the most limiting factor to bermudagrass use and persistence. When it comes to nutritional inputs, like N, the short answer is yes, N applications do strongly affect pretty much anything in the turfgrass plant including winter hardiness/survival. Remember that N dramatically drives greening and growth but… when it comes to winter hardiness it has taken a series of studies to clarify this issue and gain an understanding about how much seasonal or late-season N might affect winter hardiness. It is also important to mention that winter survival is a complex issue as numerous factors affect survival. Tese factors include: low temperatures (e.g. how low?), duration of low temperatures (e.g. how long and when does this occur in the winter?), soil compaction, traffic, duration of the growing season (e.g. how long is the healthy growing season?), plant hydration status, cultivar selection, is the area prone to spring dead spot? was the area overseeded with ryegrass? and more.
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DOES NITROGEN STATUS MATTER? Remember, if (or when) bermudagrass dies during winter it is rarely one single factor that has caused death. A nice early outline of this topic was presented by Chalmers (1986). Further, in areas where winter injury is a major concern, one of the most important things any turfgrass manager can do is plant a cold hardy cultivar. Currently, there are numerous reliable cold-hardy improved vegetatively propagated cultivars that have done reasonably well with winter survival in our field test plots in West Lafayette. Among the commercialized cultivars these include: (in no particular order) Northbridge, Tahoma 31, Iron Cutter, Patriot, and Latitude 36, as well as others that are available around the U.S.
Understanding bermudagrass winter survival has had a complicated history of research. Some of the early reports included work by Chalmers and Schmidt (1979) and Beard (1982). For example, in Beard’s work, he reported that late-season (e.g. late summer/early autumn) N applications increased “the vulnerability” of bermudagrass to winter kill and promoted winter disease. Tis was based on information from Texas and presumably based on the hypothesis of more active, succulent growth going into the colder months. Further, in the Chalmers and Schmidt work, they were working off the reality that cold hardiness levels are not static during the dormancy/semi-dormancy period. A level of hardiness varies based on plant maturity, physiological age, prevailing temperatures, day length, plant moisture content, and mineral nutrition (e.g. N-P-K levels, etc.).
With these factors in mind, maximum winter hardiness generally occurs early in the dormancy period and declines during late winter (likely due to a slow exhaustion of carbohydrate reserves). When late-winter warming occurs, the plant begins to “deacclimate” and if the plants are exposed to severe temperatures (e.g. hello FALSE SPRING!) winter injury can be more damaging. Tus, Chalmers and Schmidt attempted to “ascertain the effects of low temperatures on ‘Tifgreen’ bermudagrass at several
TPI Turf News May/June 2024
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