By W.P. Ryan

An old advertising campaign touting Minnesota as a golf destination proclaimed beneath an image of a verdant tree-lined fairway, “The deeper the snow, the greener the grass. Don’t ask us to explain.” Given the hefty amount of snowfall Minnesota experienced this winter, creators of that decade-old ad campaign may be hard-pressed to explain the turf damage experienced this spring by several Twin Cities golf courses. With the recent spring thaw and the start of the golf season, some courses have turned to temporary greens as a result of “winter kill.”

Winter kill is the kind of term that many golfers bandy about knowingly, yet it’s a subject few outside of turf professionals really understand. Ironically it’s not the snow or its depth that wreaks havoc on our fairways and greens. Rather it’s a combination of timing, thaw-and-freeze cycles, and snow and ice coverage.

“Winter kill is a non-specific, generic term meaning ‘death of grass’,” says Brian Horgan, a turfgrass extension specialist and Ph.D. at the TROE Center (Turfgrass Research, Outreach and Education), at the University of Minnesota, St. Paul. There are four causes of winter kill, Horgan explains, desiccation, low-temperature kill, crown hydration and anoxia. Desiccation, as it implies, is death brought on by exposure to winter winds. Low-temperature kill occurs when plants are exposed to a lethal drop in temperature.  With crown hydration, the plant virtually explodes after a snow or ice thaw and sudden refreeze. And anoxia is the toxic build up and trapping of poisonous gasses under an impermeable layer, like ice, that kills the plant. Conditions for toxic build up include shallow frost, warmer soils, long ice cover, and more bug activity.

“Carbon dioxide is the primary gas that we look for with anoxia,” says Horgan, adding, “if it’s greater than ten percent under the ice, it triggers death.” 

While golfers are busy making holiday plans, in November and December, or gearing up for the golf opener, in March and April, nature’s silent killers are at work on our turf.

“The shoulder season is when we see most of the death,” says Horgan. He advises golf course superintendents to take samples of their turf, both healthy and in areas prone to death, and bring them indoors to develop. What they find will help them prepare for what’s to come when the snow melts and warmer temperatures arrive. It may mean ordering more inputs, like seed, or, in the case of serious winter kill, blogging to forewarn members of damaged turf.

“Today is tough,” explains Horgan, referring to the cooler conditions in early April when the soil is not yet warm enough for turfgrass growth. With warmer nights (or with the aid of coverings such as Evergreen^TM turf covers), superintendents and golfers alike can expect Minnesota’s turf to green up. Come summertime, golfers will find the luxuriant turf promised in that old advertising campaign. 

At the TROE Center, turf scientists are developing a perennial ryegrass better suited to Minnesota’s cold climate. The future looks like more regulation, Horgan says, pointing to Europe as an example. Key to that future is developing new species of grasses that require less inputs (nutrients, pesticides and water).  We’ll visit with Horgan this summer to take a closer look at the work going on at TROE, and report back.