Winterkill has hit a lot of courses in Michigan hard over the past several years. On my home course, several greens required major reworking after the winters of ’13/’14 and ’14/15′. In my nearly thirty years of teaching, those are the only two winters in which I remember schools being closed because of cold. The severe temperatures and deep snows of those two seasons froze the greens down to their base and starved them of sunlight, killing the grass for the summer.
I am also worried about this season, where a snowy and cold December has been followed by a warm January. That is sure to be followed by a frozen February. The freeze-thaw-freeze process is not good for the grasses.
Winterkill, according to the USGA is:
a catch-all term describing winter injury to turfgrass that occurs through a variety of mechanisms such as ice suffocation, crown hydration, low-temperature injury and desiccation. Identifying the exact cause of winterkill is difficult because winterkill may be caused by one mechanism or could result from a combination of mechanisms that act simultaneously or occur at multiple times during winter.
Ice suffocation occurs when a sheet of ice settles in over the turf for 75 or more days. One study concluded that the cause was the accumulation of toxic gasses. Ice also can cause damage through a process called “crown hydration,” in which grass absorbs water during a thaw, only to be quick-frozen later. That process causes ice crystals to form and destroy the crowns of the grass.
It is the crown hydration damage that seems likely to me to occur in this winter’s freeze-thaw-freeze pattern.
Low temperature injury is similar to crown hydration, as frozen soil causes ice crystals to form in the grass itself. That was likely the villain behind the damage from 2013 to 2015.
Desiccation occurs when the grass becomes overly dry on exposed or elevated areas. Probably not really a problem in Michigan. We don’t generally have water issues.
What can be done about it? Apparently not much. Again, the USGA writes:
Golf course superintendents are not able to prevent winterkill, but they can implement a variety of programs that give turfgrass playing surfaces the best chance of surviving winter. Common strategies in northern climates include converting to cold-tolerant turf varieties, implementing proper fall fertilization, raising mowing heights during fall, reducing shade, improving drainage and covering putting greens during winter.
One solution I have seen higher end courses attempt is covering greens with various fabrics. But that’s obviously not a solution for most places.
Michigan State’s agricultural extension service offers some suggestions for treating winterkill, among them:
Reestablishing turfgrass in damaged areas can be very challenging in the spring because of the cool, cloudy conditions that often persist. Depending on the extent of damage, either seeding or sodding may be necessary to facilitate recovery. In areas where the turf was killed in a manner that left well-defined margins between dead and living turf, it may be feasible to strip dead turf and sod the area. In areas where the kill was more scattered, it may be easier to seed the area.
As with anything, however, an ounce of prevention is worth a pound of cure. Switching to more hardy creeping bengrass can help. Another solution — which my local club has started — is managing drainage better. My home course installed several new greens drainage systems this past season.
Getting the standing water off the greens prevents them from re-icing. Courses also can do a better job of managing thatch. Excess thatch exposes crowns to the cold and can hold moisture that will freeze. Again, this is something my home course has started since the bad winterkill years. This past season, late season aeration and top dressing with sand was on the maintenance menu.