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There is no doubt about it, the winter of 2024-2025 was not kind to warm-season turf in the transition zone. I recently visited a number of courses in Tennessee and North Carolina with significant winter injury, but there are many others from Virginia to Oklahoma that have damaged or dead warm-season turf right now. The golfers at every course I visited thought the damage was worse at their course than others, but the reality is that this is a widespread issue that affects many courses. So, let’s take a look at what happened, how to deal with turf that is still damaged, and what courses can do to reduce their risk in the future.

While golfers may see all this damage collectively as “winterkill,” it is important to draw a distinction between turf that was injured or actually killed. That makes a big difference in options for recovery in the near term. It’s also helpful to understand the most common mechanisms for winter injury to identify what happened at your course and lay the groundwork for reducing risk in the future.

Temperatures are the primary driver behind winter injury

Without very cold temperatures, there is not going to be much in terms of severe winter injury. Take a look at Figure 1 below to see what happened this winter in Nashville, Tennessee. Dates where turf was vulnerable to severe freeze injury and winterkill are circled in blue. Additionally, each of these freezes were followed by warm spells circled in red that were well above average temperatures. Cycling between record or near-record lows and highs contributed to significant amounts of turf injury and loss.

Secondary factors play a key role

Anything that adds stress to the turf increases the potential for injury. The following is a list of some common stress factors that can increase the risk of winter injury and photos of some damaged areas from this year that illustrate the problems.

Cultivar and Species Variation: Cold-tolerant bermudagrass cultivars – such as ‘TifTuf’ and ‘Tahoma 31’ – and zoysiagrasses can withstand temperatures 5 to 10 degrees Fahrenheit lower than less-tolerant grasses such as ‘Tifway 419’ or common bermudagrass. Courses with less-tolerant varieties saw more damage, but we are still seeing winter injury on cold-tolerant varieties and zoysiagrasses. It’s important to explain to golfers that using cold-tolerant grasses reduces the risk of winter injury but nothing can eliminate it.

Turf Health: Healthy, well-maintained turf is less susceptible to winter injury.

Traffic: Traffic stress reduces overall turf vigor and increases susceptibility to winter injury.  

Shade: Turf under shade in the growing season conducts less photosynthesis and stores fewer carbohydrates, making it weaker and more vulnerable to damage. Winter shade presents a different problem. Shaded turf in winter has colder soil temperatures which increase susceptibility to injury.

Acclimation: Bermudagrass and zoysiagrass that undergo gradual cold acclimation in fall (triggered by shorter days and cooler nights) is more resilient to freezing temperatures than grass that was actively growing and then is suddenly hit with extreme cold.

Moisture Levels: Wet soils can increase freeze damage due to ice formation in tissues, while dry conditions may lead to desiccation injury. Both types of winter injury can be seen on the same golf course due to the various microclimates present.

Duration of Exposure: Short-term freezes are less damaging than prolonged cold periods, which prevent recovery and exhaust carbohydrate reserves.

What to do now?

Every golf course I visited this spring with winter injury wanted to know two things: How do we recover and how do we make sure this never happens again? When it comes to the first question, if an area is dead, sod or sprigs are the only options for recovery. However, most areas that I saw are not completely dead. Sometimes there are viable rhizomes in the soil that will stimulate new growth with warm temperatures. These areas may look terrible right now, but week by week they will fill in and by the middle of the summer 100% recovery is achieved. This is a more economical option and will likely lead to better playability in the future because there will not be sod seams and other irregularities that come with regrassing. Unfortunately, many parts of the transition zone have not had much good growing weather for warm-season grasses, so recovery has been slow.

Of course, not all courses have the patience to wait for damaged areas to fill in. They prefer to use sod to get them looking and playing better sooner, which is understandable. The option to sod produces better immediate results, but depending on the location, it can take just as long for the sod seams to grow together as it does for the area to grow in naturally. There is also the added expense to consider. The unfortunate reality is that there are no great options when winter damage lingers this late into the year.

Playing defense in the future

Even the best management practices cannot provide 100% certainty that there will be no winter injury in the future. A better way to think about it is risk mitigation. What can your course do to lower the probability that turf will get injured if we have another hard winter? The extent to which a course wants to play defense against winter injury will depend on how much or little they wish to alter the golf experience in the summer and fall, and whether they are prepared to make a financial commitment to addressing various risk factors. All the risk-mitigation strategies listed below have research behind them. Be advised that some of them will create a suboptimal golf experience at certain times of the year.

  • Reducing shade reduces the risk of winter injury and improves turf health and playing conditions throughout the year.

  • Reduce or eliminate cart traffic through the growing season and offseason. Recognize that concentrated, repetitive maintenance traffic can also be detrimental to turf health, which increases the risk of winter injury.

  • Manage soil moisture by adding drainage in wet areas and irrigating dry areas in winter to limit desiccation.

  • Increase mowing height. This is a two-step concept that prioritizes turf health over optimal playability. Courses can start by incrementally increasing mowing height throughout the growing season, followed by a more substantial increase in the fall. Higher mowing heights improve turf health and carbohydrate storage going into winter, and the additional leaf tissue provides more insulation to the crowns and protection against desiccation. However, there will be playability impacts that come with taller heights of cut. Note that zoysiagrass does not respond well to being cut shorter and then grown into a taller height of cut.

  • Use turf covers where practical, especially on greens.

  • If an area needs to be sodded and it contains a less cold-tolerant variety, resod with a more cold-tolerant variety or species.
     

Wrapping up

The moral of the story with winter injury is that it’s complex and unpredictable. Golf courses in the transition zone suffered winter injury in areas where the turf was too dry and too wet. Closely mown turf suffered but so did taller heights of cut. Cart traffic was a precursor to injury but so was concentrated foot traffic. In the end, courses that are still looking at damaged turf will have to accept that it’s going to take some time for things to get back to normal. With hard work and warm summer temperatures, golf courses can put a few weeks of bad winter weather behind them and hopefully take some steps to reduce their risk of damage in the future.