Several Curveballs from Mother Nature in 2018
abnormal (adj.) — deviating from the normal or average; unusual in an unwelcome or problematic way.
This definition of “abnormal” from the Merriam Webster dictionary certainly applies to climatic conditions faced by many turfgrass managers across Tennessee in 2018. Oddities in temperature and rainfall resulted in significant turfgrass management challenges from Chattanooga to Memphis this past season. As the calendar year comes to a close, looking back at these abnormalities can be helpful as turfgrass managers prepare for what may be headed their way in 2019.
A spring “false-start”
It didn’t take long for the abnormalities of 2018 to surface along Interstate 40 and beyond. Average air temperatures during the week of January 21st — January 27th, 2018 approached 50 F in many of Tennessee’s largest cities. This was followed by a period of even further warming with daily average air temperatures exceeding 62 F the week of February 18th — February 24th in Nashville. The result? Warm-season turfgrasses began to emerge from dormancy weeks earlier than normal. This lead to questions about whether it was too late to apply glyphosate for postemergence control of winter annual weeds. Additionally, it poorly positioned warm-season turfgrasses for the next abnormality of 2018
Prolonged cooling throughout March and April
Abnormally high temperatures across Tennessee during January and February were followed by a prolonged period of cooling that lasted throughout the entirety of March and April 2018. In reviewing data from Chattanooga, Knoxville, Nashville, Jackson, and Memphis, the average air temperature for the month of March was ~3 degrees lower at these locations in 2018 than March of the previous year. This continued throughout April with average temperatures measuring ~10 degrees lower in April 2018 compared to April 2017.
The result? Warm-season turfgrass emergence was dramatically delayed. Many bermudagrass stands did not fully “green-up” until late May. Additionally, the normal emergence pattern for summer annual weeds like crabgrass was essentially halted by this period of cooling as well. Therefore, those who timed preemergence (PRE) programs properly and applied when soil conditions were optimal (back in February) were now positioned to have them run-out during the middle of the summer. In short, warmth in February coupled with prolonged cooling in March and April resulted in our “crabgrass season” being almost eight weeks longer than normal. This created a difficult situation for many turfgrass managers given the next abnormality of 2018.
Elevated summer heat — well into the fall
Temperatures across Tennessee during the summer of 2018 were considerably higher than the previous two years. This translated into greater growing degree day accumulation during the months of May through September.
Although temperature records were not broken like they were in 2012, there were statewide consequences of the increased summer temperatures experienced by many in 2018. First, the stressful period for creeping bentgrass putting greens on golf courses was much longer than normal — in large part because September was simply an extension of August. There is typically a “countdown until September” that begins in mid-June with the promise of more favorable weather forthcoming. This was by no means the case in 2018 as temperatures in September were far warmer than they were in previous years. For example, Knoxville, Chattanooga, and Nashville experienced nearly identical average monthly air temperatures during August and September 2018.
The second consequence of this elevated summer heat was accelerated breakdown of PRE herbicides used to control summer annual weeds. The primary means of PRE herbicide breakdown in soil is microbial activity which is increased under conditions of elevated temperature and moisture. One could argue that many turfgrass managers across Tennessee experienced a perfect storm for PRE herbicide failure during summer 2018. Abnormally warm spring temperatures required applications to be made earlier than normal, therefore extending the length of time these treatments needed to be effective. During this extension, abnormally warm temperatures accelerated breakdown on these materials in soil. To that end, many turfgrass managers across Tennessee saw breakthrough of crabgrass and goosegrass during mid-to-late summer.
Wet weather during the fall
Abnormal climactic conditions continued into the fall of 2018 with several locations receiving rainfall that far exceeded totals accumulated during 2017 and 2016.
It is likely that this elevated fall precipitation will negatively affect herbicide programs for annual bluegrass control in warm-season turfgrass, particularly those incorporating soil-active herbicides applied at a PRE timing. While the consequences of this elevated fall precipitation won’t be fully felt until spring, turfgrass managers across Tennessee should be prepared in the event annual bluegrass control programs break in early spring and clean-up applications with postemergence herbicides are needed.
Moving Forward
Mother Nature seems to bring new challenges to turfgrass managers every year. To help those in the field, the UT Turfgrass program has teamed up with mesur.io to provide a new online resource for tracking climatic conditions relevant to turfgrass management. Keep an eye for this new online resource slated to debut in January 2019*.
*All data in this post were captured using a beta-version of the mesur.io Tennessee climate data center that will be coming online in January 2019.
