Multi-state study offers recommendations for keeping bermudagrass greener all season

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Whether it's a football field, a golf course, or a home lawn, a new multi-state study offers recommendations for keeping some varieties of turfgrass greener, longer.

Researchers currently based in six states collaborated to identify three simple management tips to extend the green color and reduce cold-weather injury in hybrid bermudagrass. Those recommendations include raising the mowing height, applying nitrogen fertilizer in the fall, and most importantly, maintaining adequate soil moisture in the lead-up to a short-term freeze event, such as a spring-time cold snap.

The study, "Improving winter survival of interspecific hybrid bermudagrass in the Mid-Atlantic region through cultural practices," was published in the Crop, Forage & Turfgrass Management journal in August.

Wendell Hutchens, co-author of the study and an assistant professor of turfgrass science with the Arkansas Agricultural Experiment Station, noted that although the work focused on golf courses, the recommendations could apply equally in other situations.

"The practices can be used universally," Hutchens said. "Sod growers can use the same practices, as can sports field managers and homeowners for their lawns."

Sports field managers, Hutchens added, may benefit the most from this study. Much of the work for golf courses was done on fairway-height bermudagrass, which he said is "usually comparable to sports fields."

"Many of our turfgrass professionals manage hybrid bermudagrasses throughout the Mid-Atlantic. Winter injury is one of their biggest concerns," said David McCall, co-author of the study and associate professor of turfgrass pathology and precision management in Virginia Tech's College of Agriculture and Life Sciences. "This multi-state project was designed to answer some practical questions that would benefit our industry stakeholders."

According to the study, hybrid bermudagrass is susceptible to cold-weather damage in the transition zone, an area that includes a band from Maryland and Virginia on the East Coast to Arkansas, parts of Missouri and Oklahoma, all the way to California on the West Coast. While the study highlights the Mid-Atlantic region, the work is relevant for anywhere in the transition zone, Hutchens added.

"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."

Results and recommendations from field trials

Hutchens said the research team set out to evaluate the effects of soil fertility, mowing height and moisture to avoid cold-weather injury, also known as winterkill.

"Those are three primary management practices for turfgrass, but particularly with winterkill, they play a major role," he said. "We found some pretty interesting data during the first couple of years of our study."

Roberts noted that historically, avoiding late-summer applications of nitrogen on bermudagrass was the standard.

"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 work with mowing height also yielded an interesting insight, Hutchens said.

"Mowing height didn't have a substantial effect on winterkill, but it did reduce winter weed populations when we mowed at higher heights, which is a really useful finding and a serendipitous takeaway from the study," Hutchens said.

"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.

McCall noted that these mowing heights are considerably lower than how a home lawn should be maintained.

Moisture is critical

Due to mild and wet winter conditions at the field trial locations in Maryland and Virginia, the researchers performed several experiments using freeze chambers to mimic winter weather conditions. When Hutchens started his job in Arkansas, he worked with Battaglia and DeBoer to evaluate the relationship between soil water content and level of cold-weather injury.

DeBoer, who mainly participated in the study as a Ph.D. student at the University of Arkansas before taking up his post with the LSU AgCenter, said the research found a strong association between soil moisture and winterkill symptoms.

"There is definitely a positive correlation with increased soil moisture prior to short-term freezing events, resulting in better turf survival," DeBoer said.

One possible explanation, according to DeBoer, may be a temporary heating effect from the irrigation water buffering the roots from cold temperatures. DeBoer cautioned there is a high degree of variability from year to year and site to site.

"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."

Volumetric water content is a measurement of how much water a given volume of soil contains. The amount of water that a field can hold depends on the type of soil, Hutchens noted.

"Adequate soil moisture is certainly one of the most crucial management practices to reduce winterkill," Hutchens said.

Reaping rewards from collaboration

Hutchens noted that the multi-state collaboration was a key part of the success of this study.

"You get a lot of different ideas and perspectives," he said. "This project demonstrates that these collaborative efforts across multiple universities can be really successful. It takes a lot of legwork to organize it all, and the initial work is challenging, but the rewards that you reap from it are totally worth it."

Hutchens said the team began the work in 2019 while he was a graduate student at Virginia Tech, working under McCall as his adviser. Booth was working as a research associate at Virginia Tech at the time before joining USGA. Doherty was a graduate student at the University of Maryland working under Roberts, who later took a job at Clemson University. DeBoer and Battaglia got involved when Hutchens moved to Arkansas in 2022.

"This project exemplifies the benefits of collaboration, as the primary study was performed at three geographically unique locations in the Mid-Atlantic," McCall said. "By bringing in additional resources from northwest Arkansas, we were truly able to use broad strokes for practical recommendations to turfgrass professionals throughout the transition zone with confidence that our results apply across the board."

In addition to the value of the research team's collective experience, Roberts also noted the added value of testing recommendations across multiple geographical areas.

"Collaborative efforts not only helped push this research forward, but performing field research across multiple field sites in different states enhanced the recommendations offered to growers across the transition zone," Roberts said.

In addition to Hutchens and McCall, other co-authors of the study include Joseph Doherty, former graduate student at the University of Maryland; Joseph Roberts, associate professor with Clemson University's College of Agriculture, Forestry and Life Sciences; Eric DeBoer, assistant professor with the LSU AgCenter in Louisiana; Jordan Booth, senior director of the U.S. Golf Association's course consulting service; and Michael Battaglia, graduate student at the University of Arkansas' Dale Bumpers College of Agricultural, Food and Life Sciences. The Arkansas Agricultural Experiment Station is the research arm of the University of Arkansas System Division of Agriculture.

More information: Joseph R. Doherty et al, Improving winter survival of interspecific hybrid bermudagrass in the Mid‐Atlantic region through cultural practices, Crop, Forage & Turfgrass Management (2024). DOI: 10.1002/cft2.20303

Provided by University of Arkansas System Division of Agriculture