"The transition zone is where we can grow cool-season grass and warm-season grass equally poorly."
- A.J. Powell, Ph.D.
When calculating climatological averages over time, it takes a lot of erratic highs and lows to find a happy medium. The winter of 2017-18 definitely qualifies as one of those wild lows.
Exhibit A: When Jim Brosnan, Ph.D., was making applications for goosegrass trials at the University of Tennessee turfgrass research center in Knoxville, lingering winter conditions in mid-April brought soil temperatures of 54 degrees Fahrenheit paired with air temps of 38 degrees and flurries blowing through the air.Only two months earlier, eastern Tennessee was enjoying one of the warmest Februarys on record. Average temperatures for the month were highs of 62 degrees and lows of 44 degrees, which were, respectively, 8 and 10 degrees above the historic average. A record high of 81 degrees on Feb. 22 was recorded at the Knoxville airport, and overnight temperatures dropped below freezing on only six occasions throughout the month, according to the National Weather Service. Precipitation for the month was double the historic average.
"This is the oddest winter and spring I've seen since I've been here," Brosnan said.
"I've seen the full gamut in my travels this spring. I haven't seen any dead greens, but what I have seen is differential spring green up following stress. . . . By and large, I think everyone will come out fine with good growth. They'll just be lagging."
Last fall, the University of Arkansas released preliminary data on a research project by graduate student Eric DeBoer that helps establish thresholds for exposure of ultradwarf Bermudagrasses to cold temperatures, allowing superintendents to minimize the threat of winter damage and improving spring green up throughout the transition zone.
DeBoer's research tested Champion, TifEagle and MiniVerde ultradwarf Bermudagrasses using covers at 25 degrees, 22 degrees, 18 degrees and 15 degrees Fahrenheit. TifEagle and MiniVerde proved to be more cold tolerant than Champion.
According to the study, Bermudagrass greens covered when temperatures reached 15 degrees survived throughout the winter with improved spring green up. Covered greens even survived two days of extreme cold temperatures where overnight lows dropped to 0 degrees on consecutive nights.
The weather has definitely made for a kooky start to everything."
Golf course superintendents throughout the transition zone who have made the switch to Bermudagrass during the past 15 years are covering their greens. Even among those who use covers, conditions have varied as they peeled them off, said Brandon Horvath, Ph.D., turfgrass pathologist at UT.
Some putting surfaces have been greener than others, while some have been more prone to typical spring disease pressure.
"Some turf has greened up under double covers or areas on covers where there is overlap, like along seams," Horvath said. "From a disease standpoint, we've seen all the usual suspects. In greens that have been double-covered, we've seen some pythium because it's been wet recently."
That list of usual suspects includes pythium, spring dead spot, leaf blight, take-all patch and fairy ring.
For those who might be set on a calendar for making fungicide applications, this year might be a good reason to move on from that thinking, Horvath said.
"Application timing is one of those things where it's easy to get into a run. If you're into a calendar-based thing, with the the weather the way it's been - somewhat cold still, but not terribly cold, you have to pay attention to that," Horvath said.
"For fungicides, we don't have indicators like forsythia blooms like you do with herbicides. Soil temperatures trigger when to make applications. When you have soil temperatures around 55 to 65 degrees, that's when you want to pull the trigger on those applications when soil temps are in that appropriate range. But with respect to periods like this when it gets colder, warms back up and gets colder again, you need five or six days of sustained soil temperatures to make those applications."
About 10 golf courses, mostly low-budget facilities, in western Kentucky have made the switch to ultradwarf Bermuda in recent years because they lack the budget to manage bentgrass through the state's hot, humid summers, said Gregg Munshaw, Ph.D., of the University of Kentucky.
"They only contact me if they have issues," Munshaw said. "They haven't contacted me yet this year, which means they're no problems, other than green up is just a little slower this year than they would like."
Like in Tennessee, Munshaw isn't predicting any long-term problems for the courses in western Kentucky, or anywhere else throughout the transition zone for that matter. Any damage occurring on greens should be relatively simple to fix, but will require patience from superintendents - and golfers.
"Unless there is widespread death, it's probably not going to be doom and gloom," he said. "If there is some loss, they might want to consider plugging from outside the greens, but that stuff spreads pretty well. The problem is what will members expect, or if you're a daily fee and you are relying on play coming in the door, are golfers going to come in and play if the grass is not there, or it's patchy? Because it might be late June until they are where they want to be, or maybe later. This isn't football, where you can wait until August. This is golf and you need to be ready now."
What is of more concern to Munshaw is what might happen to turf on the northern end of the transition zone if cold temperatures persist and the turf uses up the precious resources it needs to survive the winter.
"My only concern is the longer the grass stays dormant, the more it will burn up carbohydrates," he said. "If they are gone, and those places will struggle with green up. We need that turf to start waking up now."
The wild temperature swings throughout the transition zone from winter through mid spring have created some challenges for weed control as well, Brosnan said.
Warm temperatures in February led to some early green up and put into question whether it was safe to make applications for Poa control since the turf was beginning to emerge from dormancy.
At a recent Middle Tennessee chapter meeting, superintendents were discussing early damage from Poa control applications, Brosnan said.
"It was so cold in January, then in February the weather broke like there was no tomorrow," Brosnan said. "We had high temperatures and high amounts of rainfall. We exceeded the 30-year rainfall average in just about all the major cities in Tennessee.
"We reached 100 growing degree days in February, and that made for unsettling decision on Ronstar and Roundup. Then we'd have frost for the next four or five days. I know you're no longer accumulating growing degree days when it's that cold, but does that reset the clock? "The weather has definitely made for a kooky start to everything."