By Eric Watkins, Ph.D.
As a researcher, on one of the first warm days of spring, when snow drifts are reduced and the last few shards of ice remain, I hope to find a few plots that have succumbed to winter’s ills. “Is that snow mold damage?” “Yes, I think that annual bluegrass might have died from our ice treatment!” “Shoot, that tall fescue looks almost too healthy.” Turfgrass managers, however, seek signs of hope and a smooth transition to spring sports seasons. “I don’t think that perennial ryegrass is quite dead yet!” “That snow mold will be a cinch to rake off in a week or two.” “We sure dodged a bullet from that January ice sheet.”
As long as there has been managed turfgrass, damage from winter stress has been a problem, and this problem has been difficult to solve. Even with the bounty of technologies and tools available to modern turfgrass scientists, we have been unable to provide effective solutions to reduce winterkill risk on turfgrass surfaces. Of all the things we study in our turfgrass research program at the University of Minnesota, winter stresses are by far the most challenging.
For other stresses, our approach is more straightforward. When our goal is to find creeping bentgrasses that grow well on greens in Minnesota, we simply plant a trial that includes several varieties, and see which one looks best in a few years. There isn’t much nuance to this process – seed, fertilize, mow, evaluate, repeat. The variety that handles the conditions at our research facility the best will be at the top of the leaderboard, while those that lag will endure the harsh reality of low scores and possibly even lower seed sales.
Unfortunately, investigating winter stress damage of turfgrasses – and finding solutions to prevent damage – is not nearly as easy. Why is this? Does it have to be this way?
Winter is different from year to year
Anyone living where winter weather is a regular part of life understands all too well the vagaries of the season. One year might bring a cold November that puts all the grass into a nice dormant state followed by deep layers of snow that give their quiet protection to turfgrass surfaces until a timely spring melt starts up, followed almost immediately by great grass-growing weather. Another winter might bring warm temperatures in November, followed by a rainy December, and a cold January that turns pools of water into rinks of ice. Yet another winter bounces around from cold to warm to dry to wet and back around again – each time causing the grass to spend energy trying to survive the changes. Will turfgrass survive these conditions? It depends. Creeping bentgrass and Kentucky bluegrass would probably survive in all cases. Perennial ryegrass might struggle in the second and third situation (see Figure 1).
Winter changes from here to there
If you’ve ever experienced a major snowstorm, you’ve likely been interested in how much snow you received. You’ll take regular looks out the door, trying to ascertain how many inches of snow have fallen on the patio chair you forgot to put away in the fall. After the storm ends, you’ll go outside and try to find a representative place to measure the snow, or maybe take measurements at several locations and calculate an average. A drift of several feet might sit just beyond the porch, while the nearby lawn is almost bare. These changes in snow depth are a big problem for turfgrass field research. A few inches of insulating snow here or there could be the difference between plant survival and plant death.
Similarly, when water pools after a winter rain or when ice melts then freezes again when temperatures drop, two adjacent areas might have differences in ice thickness, color or smoothness. These inconsistencies over small spatial areas create problems when trying to conduct research that requires consistent conditions over a research trial. These microclimate differences are always present, even during summer research trials, but they are not nearly as disruptive to research in the summer as they are in the winter.
Winter isn’t everywhere
Every turf surface needs to be fertilized. Most professionally managed surfaces need pesticides or plant growth regulation. Topdressing is agnostic to location; not so with winter stresses, at least the most severe cases. For much of the world, winter isn’t a big deal when it comes to turfgrass management, so the number of turfgrass managers dealing with this challenge is not that big compared to the overall population of turfgrass professionals. Therefore, funding and attention are diverted toward broader needs – efforts that will have a greater bang for the buck.
A different approach to winter research
It’s clear that turfgrass managers need more research-based tools and solutions to reduce winter injury risk, so we needed to come up with an approach that wasn’t restricted to a single place or year. Within a given winter, there will always be damage somewhere; so we wondered if we could somehow track damage across space and time to learn how and why grass was dying, then come up with solutions to prevent winter damage.
Winter damage affects all sorts of turf surfaces, sports fields included, but perhaps the most widespread managed turf surface is the golf green. Although golf greens don’t cover a vast area, there are a lot of them, and greenskeepers typically have very good records of their management and performance. We also know that winterkill of golf greens is a major concern of most golf course superintendents in cold climates. Given all of this, we decided to study individual golf greens throughout the world, under the assumption that every year we should be able to find a few instances of severe winter damage and many instances where there was no damage. Both cases are important, as we need to make comparisons between those combinations of environmental factors that do cause grass to die and those that do not (we call these “envirotypes”).
With the help of the Genetics, Environment, Management and Socioeconomics (GEMS) Informatics sensing group at the University of Minnesota, led by Dr. Bryan Runck, we were able to deploy several dozen environmental sensing nodes on greens throughout North America and northern Europe (see Figure 2).
Photo by Andrew Hollman.
Each fall, the GEMS team ships out nodes to collaborating golf courses, and the superintendents at these courses install the units on a green that is prone to winterkill. All winter long, every 15 minutes, those sensors record several variables – including soil and air temperatures, concentrations of oxygen and carbon dioxide, relative humidity, light, and air temperature. The data are automatically uploaded to our database via a cellular connection.
At the same time, we ask superintendents to provide information on the health and management of the green (i.e., Was it in good shape going into winter? Did it get damaged during the winter? Did you spray snow mold fungicides?). They also make weekly observations and measurements on the green (How deep is the snow? Is there any ice?).
We also can access data from satellite imagery and pull data from other public weather databases. All of the information – from humans, satellites, weather stations, and the environmental sensing nodes – gets used by computer scientists to understand how grass is or isn’t dying during the winter. Then the rest of our team – made up of plant physiologists, plant pathologists, plant breeders and turfgrass management specialists – uses the results of those analyses to design studies that aim to offer new knowledge and recommendations about reducing turfgrass winter stress damage risk.
While the data we are analyzing come primarily from creeping bentgrass and annual bluegrass greens, the things we are learning are being readily applied to other species, such as perennial ryegrass, that are important for sports field managers. As part of this “WinterTurf” project, we are carefully studying perennial ryegrass plants to see the types of changes they undergo during the fall as they prepare for winter. By doing so, we hope to find some physiological changes in winter-stress-tolerant perennial ryegrass plants that give the plant an advantage during the winter. Plant breeders could then select for traits associated with this change, leading to perennial ryegrass varieties that are more winter hardy. For example, researchers on our team recently discovered that differences in perennial ryegrass xylem vessel diameter may be associated with differences in low-temperature freezing tolerance.
We have much to learn, and hopefully many more winters of frigid research activity. In the meantime, we hope to communicate new ideas for getting turfgrass through winter to turfgrass practitioners of all types, with the hope that we can finally figure out winterkill. Currently, there are projects in the field at multiple university research sites investigating non-chemical snow mold control options, the use of heavy topdressing to reduce winter injury risk, and ways to improve early spring seeding success. You can stay abreast of new developments from these projects and others by visiting winterturf.umn.edu and signing up for our monthly email newsletter.
Eric Watkins, Ph.D., is a professor in the Department of Horticultural Science and vice provost for distributed learning at the University of Minnesota. His research program is focused on identifying turfgrass mixtures for Minnesota roadsides, germplasm improvement of several turfgrass species, and projects investigating approaches to reduce winter damage on cool-season turfgrasses. In his administrative role, Watkins provides leadership for online educational programs across the five-campus University of Minnesota system.
This project was supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, Specialty Crop Research Initiative under award number 2021-51181-35861. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and should not be construed to represent any official USDA or U.S. Government determination or policy.