As the summer begins to wind down, superintendents start working on their plans to protect turf from the oncoming threat of winter injury. For some, those plans include turf covers. While they can be very effective at providing additional insulation for turf and protect it from direct low-temperature injury, getting the most out of turf covers can be an art form that requires the right timing and proper preparation.
Here are a few tips to make sure that this winter, your course is covered.
Start off right
If the timing is right, a turf cover can work incredibly well in climatic zones where winter desiccation is a problem, says Dr. Nick Christians, professor in the department of horticulture at Iowa State University.
“Desiccation is one of the biggest problems in the drier parts of the Midwest, and for that a turf cover can work miracles,” he says. “I’ve seen turf under a cover that is just way ahead in the spring when it comes out, so they definitely have a positive impact.”
But choosing the right time to put down turf covers can be difficult, especially since putting them out is labor-intensive and means closing, he says.
There’s no solid rule as to when turf covers should go out, either in soil temperatures or time of year, but superintendents need to wait until the turf has at least started to go dormant, he says. In the Midwest, that could look like mid-November or early December, depending on the weather. As the weather starts to shift and after the last mowing of the season, get started on putting out your turf covers, Christians says.
Talk it out
Communication is key when working around players in most aspects of turf maintenance, and turf covers are no different. Closing the course to handle turf covers is never going to be popular with members.
“They’ve got to communicate very well with the golfers or membership if they’re in a private club,” Christians says. “Tell them what you’re doing and why you’re doing it, because they’re not going to like it. You put a cover on, and the weather gets nice, and they’ll want to golf.”
Talk about the process and what kind of labor and cost goes into keeping turf safe from winter injury going into spring. Transparency in maintenance projects can go a long way in smoothing over membership struggles, especially if it means faster green-up when the weather improves.
Pick the right cover
There are different types of turf covers, and each can be used for different effects with overwintering turf, says Dr. Paul Koch, turfgrass diagnostic lab director at the department of plant pathology at the University of Wisconsin-Madison.
An impermeable cover isn’t going to allow any gas exchange between the plant and atmosphere, trapping certain gases just like a long duration ice cover, he says. But if a superintendent is looking for protection against winter crown hydration injury, it’s probably the right choice.
“If you have an impermeable-type cover, you’re going to need to go in and vent to provide some gas exchange artificially by blowers or putting in some PVC pipe,” he says. “Especially in the spring, it can promote growth of the plant before you necessarily want the plant to really grow.”
The temperature under the tarp heats up quickly as outside temperatures rise in the sunlight, and turf could be greening up in February or early March, he says.
Pulling the cover off after the turf begins to grow in earnest, it “could be not very acclimated to the winter conditions, and you can have some stress or freezing injury that can occur on those plants,” he says. “You can’t just put the cover down and forget about it.”
If a superintendent is looking more for a faster green-up in the spring, a permeable cover might be a better choice, he adds. There’s less concern around the prevention of gas exchange with a permeable cover.
The common recommendation from USGA and many turf experts is that if night temperatures are expected to be below 25 degrees or lower, turf covers should be deployed. But turf studies show that’s not necessarily the case, says Dr. Mike Richardson, professor in the department of horticulture at the University of Arkansas.
“If that’s your threshold, in some areas of the country, you could be covering about 15 to 20 times a year, and that’s a lot,” he says.
Richardson’s research, focused on reducing the threshold target to see how many coverings can be saved during the season, showed that superintendents can often wait for a slightly lower temperature without a significant increase in injury, he says. The research ran plots that were covered at 25, 22, 18 and 15 degrees as the target low temperatures.
“What we found out when we did this trial three years in a row, that we really had minimal differences between covering them at 25 degrees and covering at 15 degrees,” he says. “A couple times we saw a little bit more injury at 15 degrees, but we never saw death and destruction like we did with our uncovered plots, where we basically had not one single blade of grass still alive.
Richardson gives a strong caveat that the research doesn’t describe a one-size-fits-all situation. If a superintendent has the resources and the member pressures to deliver high-performance turf very quickly after the season warms up, “I would err on the side of being conservative,” he says.
For a course running a skeleton crew, he would probably start by pushing the target temperature down to about 20 to start, before proceeding on to 15.
“It would save you a lot in terms of the labor cost as well as the lost revenue by moving that number down,” he says. “We’ve done some cost analysis on that, and in some scenarios, it could save from about $15,000 to $20,000 just in labor costs, depending on the location and the year, without sacrificing any loss in the turf.”
Break the mold
Research has shown that working with a snow mold can increase susceptibility to and severity of snow mold, says Koch. This is especially true of impermeable turf covers, where snow mold pressure can as much as double. “Just make sure you have a good strong snow mold program under those covers,” he says.
An effective snow mold control should include at least two but most likely three different active ingredients from different chemical classes, he says.
Wet it down
Another area of research for Richardson shows that when covers are off, it’s critical to keep the greens hydrated. If a superintendent is in an area where the irrigation is charged and useable through the winter, “I always tell superintendents, if the covers are not on them, water them,” he say Just keep as much moisture as you can in that system.”
Wetting agents can also be used to keep water moving in the soil profile, even during the winter with dormant greens. Research results have been inconsistent, but there have been a number of occasions where wetting agents have also enhanced survival, he says.
“Again, this is pointing to the idea that desiccation is causing more injury than we may think,” he says. “The use of a wetting agent or app or two in the winter, plus putting down moisture on the greens as often as you can; just moisture management is important in conjunction in using turf covers.”
Use a probe to find the appropriate target moisture level, especially since as grass is dormant in winter, it’s much more difficult to spot stress, Richardson says.
Pull it off
Finding the right date to remove turf covers in the spring is just as problematic as finding the right starting date. It’s safer to err on the side of pulling them up too early rather than too late, says Koch.
“Pulling them up too late, you get a situation where you’ve really heated up the soil temperature under the covers,” he says. “Those plants are totally deacclimated to the winter. So, when you pull the covers off, they think it’s July when in reality it’s March.”
Superintendents can’t rely on air temperature, because it’s not necessarily going to be tied to the soil temperature under the turf covers, he says. As a general rule, pull the turf covers up at the earliest opportunity during the winter when it seems like all the snow and ice events for the season are finished.