A Sluggish Start for Bermudagrass in 2018
Why are our fairways brown?
It’s May. Why isn’t the grass growing?
My lawn wasn’t brown in May last year. What changed?
These are common questions that many turfgrass managers have been answering across Tennessee during the spring of 2018. Golfers, greens committees, coaches, and even homeowners are all interested in why bermudagrass is off to such a sluggish start this season. A look at meteorological data from across the state reveals a compelling story about why bermudagrass is behind pace in 2018.
Abnormally Cold Winter Temperatures
Most locations across Tennessee experienced abnormally cold temperatures for extended periods of time in January 2018. For example, air temperature fell below freezing (32 F) for > 20 days during January 2018 in Knoxville, Chattanooga, and Memphis. Moreover, temperatures failed to raise above freezing for 5–8 days during January.
This extended duration of freezing temperatures is concerning in that it can result in bermudagrass winter-kill from issues related to ice formation (either within or outside plant cells), direct low-temperature exposure, wind-induced dessication of leaf tissue, or combinations thereof. Stands of turf that are subjected to additional stresses (e.g.shade, traffic) are especially prone to this phenomenon, as are stands of immature bermudagrass.
Winter protective covers are often used on hybrid bermudagrass putting greens to mitigate the potential hazards associated with prolonged periods of low temperature during winter. A typical protocol involves placing a protective cover on putting green turf when temperatures are forecasted to fall below 25 F. Even surfaces that were protected in this manner are showing delayed green-up (albeit in stressful micro-environments) this spring.
Below Average Temperatures and Above Average Rainfall in Spring
The second factor affecting the slow rate of bermudagrass green-up this spring has been a combination of below average temperature combined with above average rainfall. While most locations across Tennessee experienced a spike in temperature in February, air temperatures during March and April have been at or below 30-year averages.
A closer examination of Knoxville air temperature data would indicate that conditions are approximately two-weeks behind normal. Below is a chart created by Dr. Micah Woods plotting average air temperature data for Knoxville in 2018 (blue line) compared to the 30-year average for Knoxville (green line). Assuming that sustained bermudagrass growth won’t occur until the daily average temperature exceeds 54 F (red line), this benchmark was not reached until mid-April in 2018. Comparatively, 30-year average data show that this benchmark is typically reached during mid-March in Knoxville.
Above average rainfall has not helped bermudagrass green-up this spring. Below is a series of charts illustrating above average rainfall totals for many locations across Tennessee during spring 2018, including record rainfall in February. Rainfall is an indicator of cloudy skies reducing the light available for optimal growth. Bermudagrass requires a daily light integral in spring ≥ 20 mol per square meter at lawn height with requirements being even greater on putting greens. Estimated daily light integral data for several Tennessee cities have been previously published for comparison.
With sunny skies across much of the state this past week and daily maximum temperatures exceeding 80 F at many locations, hopefully bermudagrass will turn the corner and yield the turfgrass quality that so many are craving right now.
