Winterkill is the term that describes any injury to turfgrass during the winter season. Turfgrass damage and death may be from low air temperature (very cold), desiccation (dry and cold) or diseases (snow molds). Direct low-temperature kill is caused
by crown hydration or ice and is common in sites lacking drainage. Water collects at the turfgrass crown, followed by freezing temperatures, and then water moves out of plant cells where it freezes and ruptures plant tissues. Winterkill from prolonged
ice cover is from toxic gas accumulation (butanol and ethyl butyrate) or anaerobic conditions due to oxygen depletion.
So, after putting greens suffer winterkill, is it possible to seed into the existing damaged and dead turf to quickly reestablish a playable surface? To find that answer, research was conducted at the Hancock Turfgrass Research Center at Michigan State
University in East Lansing, Mich. This was a two-year field study. A different creeping bentgrass putting green was used for each year, and both were composed of 90% sand root zone with pH = 7.7. Individual test plots were 4 feet × 6 feet (1.2
× 1.8 meters), and all treatments were arranged into three replications. Treatments included various combinations of seeded species and cultivars, cover and fertilizer.
Winterkill was simulated by applying glyphosate herbicide in October, March and early April of the first year’s field study. The second year it was applied in mid-April and late April. Following glyphosate applications, no green turfgrass tissue
was observed to confirm successful simulated “winterkill.”
The “dead plots” were seeded with Penn A-4, Providence or Alpha creeping bentgrass, or annual bluegrass. The annual bluegrass seed was a clippings/florets mixture collected from an annual bluegrass putting green at the research center. Botanically,
the floret is a flower enclosed within two bracts (the lemma and palea) that contain the caryopsis (true seed). The seeding rate for all plots was 2 pounds per 1,000 square feet (10 grams per square meter). Plots were prepared by using the Jobsaver
attachment (Miltona Turf Tools; White Bear Lake, Minn.) on a Jacobsen GA-30 aerator (Textron; Providence, R.I.), which formed about 1,000 cone-shaped depressions per 10 square feet (0.9 square meter), each one 0.5 inch (1.3 centimeters) deep. Seeding
was done by hand in late April the first year and early May the second. Immediately after seeding, all plots received the same amount of topdressing sand, starter fertilizer and irrigation.
Seeded plots were covered with 0.004-inch (0.102-millimeter) clear polyethylene plastic. Another set of plots was not covered. Plots were covered in late evening when nighttime temperatures were forecast ≤ 50 F (10 C) and removed the following morning.
Covers were removed during the day to simulate greens kept open for play during reestablishment. One week after seeding, all plots received fertilizer treatments of liquid urea (1 pound nitrogen per 1,000 square feet [5 grams nitrogen per square meter];
46N-0P2O5-0K2O) every seven days, or granular starter fertilizer (3 pounds nitrogen per 1,000 square feet [15 grams nitrogen per square meter]; 19N-25P2O5-5K2O) every 21 days. Fertilizer treatments were applied for an 11-to-12-week period.
What did the researchers observe after seeding three creeping bentgrasses and one annual bluegrass into dead turf in the spring, all covered or uncovered, and all subjected to two fertilizer programs? Combining data from both years’ field studies,
all three creeping bentgrass cultivars averaged 64% to 94% plot area reestablished by 12 weeks after seeding. Annual bluegrass only achieved about 50% plot area reestablished at 8 to 12 weeks after seeding. Therefore, seeding creeping bentgrass into
a winterkill-affected putting green in late April or early May would slowly and eventually restore most of the playing surface by late July or early August. However, seeding annual bluegrass was not helpful.
With all creeping bentgrasses and annual bluegrass plots, covering with plastic didn’t help compared to leaving the plots uncovered. Also, neither fertilizer program provided any noticeable advantage with reestablishment.
Seeding creeping bentgrass or annual bluegrass into a severely compromised putting green surface in the spring — and wanting that playing surface restored quickly — is a serious challenge. As my friend likes to say when faced with a difficult
task: “… it’s hard L-L” (referring to his favorite rapper, LL Cool J).
Source: Frank, K.W., E.N. Bogle, J.M. Bryan and J.M. Vargas Jr. 2017. Putting green establishment following winterkill. International Turfgrass Society Research Journal 13(1):250-255 (https://doi.org/10.2134/itsrj2016.04.0249).