New study offers recommendations for keeping bermudagrass green all year long

A collaboration between land-grant universities across six states revealed three key management tips for extending the green color and reducing cold-weather injury in hybrid bermudagrass.

According to the study, raising the mowing height, applying nitrogen fertilizer in the fall and maintaining adequate soil moisture in the lead-up to a short-term freeze event, such as a spring-time cold snap, are all effective practices that can be applied in various situations.

The study, “Improving winter survival of interspecific hybrid bermudagrass in the Mid-Atlantic region through cultural practices,” was published in August in the Crop, Forage & Turfgrass Management journal. Co-authors of the story include:

• Joseph Roberts, associate professor with Clemson University’s College of Agriculture, Forestry and Life Sciences
• Wendell Hutchens, assistant professor of turfgrass science with the Arkansas Agricultural Experiment Station
• David McCall, associate professor of turfgrass pathology and precision management in Virginia Tech’s College of Agriculture and Life Sciences
• Joseph Doherty, former graduate student at the University of Maryland
• Eric DeBoer, assistant professor with the LSU AgCenter in Louisiana
• Jordan Booth, senior director of the U.S. Golf Association’s course consulting service
• Michael Battaglia, a graduate student at the University of Arkansas’ Dale Bumpers College of Agricultural, Food and Life Sciences.

Roberts said that some of the recommendations go against previous industry standards such as avoiding late-summer applications of nitrogen on bermudagrass.

“Healthy roots are vital to winter survival, and it was thought that fall fertilization could favor lush foliar growth in lieu of root growth, therefore increasing chances of winter injury,” Roberts said.  “However, our research showed that slow-release nitrogen applications through mid-September had either no impact or in some cases, positive impacts on turfgrass quality and color.

“More importantly, no negative impacts were observed as a result of late-season nitrogen applications,” he said.

The study also suggested that these new practices can be used universally, whether it’s golf course or sports field management, sod farming or homeowners for their lawns.

According to the study, hybrid bermudagrass is susceptible to cold-weather damage in the transition zone, an area that includes a horizontal band across the U.S. from Maryland and Virginia to Arkansas, parts of Missouri and Oklahoma, and then all the way to California on the West Coast. Although the study highlighted the Mid-Atlantic region, its authors suggest the work is relevant for anywhere in the transition zone.

“The transition zone is where cool and warm climates meet,” Hutchens said. “That’s where we can grow every species of turfgrass — warm season and cool season — but they all struggle to some degree. And that provides ample research opportunities.”

Study recommendations

The research team aimed to better understand the effects of soil fertility, mowing height and moisture on avoiding cold-weather injury, also known as winterkill, as these are three primary turfgrass management practices.

The team found that while mowing height didn’t significantly affect winterkill, it did reduce winter weed populations when we mowed at higher heights.

“The general rule of thumb is to increase mowing heights slightly as bermudagrass approaches winter dormancy,” McCall said. “How much depends on the starting point while actively growing in-season.

“In our study, 0.75 inches seemed to be the sweet spot, though we did not see consistent impacts of mowing height on winter injury. We did, however, notice that mowing lower at 0.5 inches opened the canopy enough for weeds to germinate much more frequently, and mowing at 1 inch sometimes slowed spring green up a little,” he said.

Unlike mowing height, the team found a strong association between soil moisture and winterkill symptoms by performing several experiments using freeze chambers to mimic winter weather conditions.

According to the study, an increase in soil moisture prior to short-term freezing events resulted in better turf survival. DeBoer said this could potentially be due to a temporary heating effect from the irrigation water buffering the roots from cold temperatures, but there was also high variability year to year between test sites.

“It’s not cut and dry, say, to irrigate your soil to 25 percent volumetric water content before a freeze, and you’ll be fine,” DeBoer said. “The idea is to avoid having droughty soil before a freezing event.”

Hutchens said the team began working on the study in 2019 across multiple geographic locations. Read the full story on Clemson University’s news page on its website.

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