Quick March Bounce Back from Frigid February
Wild swings in temperature have been the story over the last six weeks, with a mild March start replacing an extremely frigid February. Winter was trending mild again, until the 7th coldest February on record dragged a warm Dec-Jan down to the first below average meteorological winter in the last six years. The harsh two-week cold snap from Feb 6-19 averaged more than 20 degrees below normal, resulting in the coldest two-week period since December 1989. The coldest air settled in the western and northern portions of the state on the morning of Feb. 16, with -26°F recorded. For historical purposes, the coldest span on record in Missouri was during the Great Arctic Outbreak of 1899, when the great Mississippi River grown to halt with ice (https://www.ncdc.noaa.gov/news/climate-history-great-arctic-outbreak-february-1899).
March Brings in the Mush
Winter 2020-21 was slightly drier than normal, but luckily for most a somewhat comforting blanket of snow was in place prior to the February frigid fright. March again proved to be divergent with extreme precipitation events over the last four days, resulting in extreme rainfall totals along the I-44 corridor and flood warnings in the Springfield area. At least an inch or two inches has fallen across much of the state, with more expected over the next few days.
While temperatures are forecasted to stay mild and rainy in the short-term, longer range forecasts are a bit unsettled, not unusual for this time of year. Through the end of the month though, there aren't any indications for a large upswing in temperatures, which should put spring greenup, along with plant metabolism and pest activity on a steady course.
Soil Temperature Guide to Early Spring 2021
The soil temperature graph above show both the story of the current spring status and the past of February's wintry blast.
Let's start with the past and give a brief outlook on potential winterkill. As noted in the weather report, the two-week span from February 6 – 19 was one of the coldest in Missouri history. The span is easily discernable on the soil temperature graphs above, but note that two-inch soil temperatures are not crashing to the negative air temperatures experienced during the period. Thankfully, most, if not all, of Missouri had a decent snowpack that served to insulate warm-season turfgrasses and lesson the chance of winterkill like we experienced in 2019 (click here to see April 23, 2019 report). This past winter was not as wet as the 2019 winter (5th wettest on record), and although February 2021 was colder, Dec-Feb 2021 as a whole was considerably warmer than the polar vortex winter of 2013-14. Average two-inch soil temperatures for the three winters were 30.3°F for 2013-14, 34.0°F for 2018-19, and 33.1°F for this past winter.
There is some concern for warm-season grasses, however, and this would be the time to bring a core into your office, home or greenhouse and see how it greens up. The wet weather in the last 4-6 weeks (current rain and snowmelt) and the resultant mush could cause issues, particularly on northern slopes or poorly draining soils. Pay particular attention to zoysiagrass areas that needed resodding in 2019 since they will still be somewhat young and more prone to damage. Also, the 2019 event is an indication that the microclimate in the area predisposes it to winter damage.
Last, but not least, some reports in the last few days have come in regarding damage on bentgrass putting greens, particularly on low lying, water collection areas. In these cases, we surmise that pooled water from snowmelt refroze, and a shift on the surface sheared the roots away from the crowns. These areas will need to be resodded or seeded soon, with drainage investigated.
NOTE: To view the current soil temperatures in Missouri, check out the Threshold Charts section here.
A brief temperature surge last week pushed the daily two-inch soil temperatures near the 55 F, and pushed some plants into spring mode. Throughout the state, though, the 5-day two-inch soil temperature average did not make it to the 55°F mark, indicating it's still a bit too early for crabgrass preemergent applications and prevention of fairy ring on golf putting greens. A lot of spreaders were spinning on neighborhood lawns around mid-Missouri during the warm spell, and if it was a preemerge application, a split application schedule better be planned. Early spring overseeding for higher cut cool season turfgrasses was probably well played, however. If fertilization, hopefully the recent deluge of rain didn't move it into our waterways.
Forsythia near warm buildings is starting to bloom, daffodils are breaking out of the ground, and redbuds are starting to show color in mid Missouri. These phenological indicators at least in mid Missouri are a little early considering the impending cool forecast for much of March, and that historically our last spring freeze event has yet to occur.
I've written ad nauseum in past reports (2016, 2017, 2018, 2019) about this fantastic service headed up by Dr. Kevin Frank at Michigan State University. Version 4.0 is up and running, incorporating a dozen models into the system to serve a large swath of states including KS, MO, IL, IN, etc. For a more personalized service I suggest making a profile and signing up for email alerts here - http://www.gddtracker.net/alerts/view/. The "target" indication for Proxy/Primo spring prevention of Poa annua seedheads is in effect, and Missouri is indicated in the optimum time frame for crabgrass/annual bluegrass preemergence, (which we are forecasted to stay in over the next seven days). One of my favorite portions of the site is comparing the current year GDD data to the previous year. As of yesterday, (3/15) Columbia is running 53 base 32 GDD and 26 base 50 GDD ahead of 2020.
Pat Guinan, the weatherman and Missouri state climatologist designed a very useful website that analyzes data from 1981-2010 to determine the probability of a freeze event ranging from hard freeze (24°F) to moderate (28°F & 32°F) to a light frost (36°F). While every spring is obviously different, this site provides an important historical framework for when less hardy plants should go in the ground. For golf superintendents, this information may also indicate a likely date when you don't have to give the morning call in to your pro shop to hold golfers back for another long sip of coffee in the 19th hole. Also for crabgrass control, the last typically hard freeze (<28°F) will occur 50% of the time in early April or late March for most of the state.
Last but not least, spring preventive applications for large patch control on zoysia fairways should be considered soon. This slow steady climb in spring temperatures and wet weather pattern greatly enhances the severity of this disease, by not allowing zoysia to wake up quickly and tilting the environment in favor of a more rapidly growing large patch pathogen population.
While there is no environmental threshold developed for timing this application, the adage has always been to apply when zoysia greens up to 40-60% or after the first mowing. In prior research, we have found spring applications to be more effective when made earlier in the spring season on areas that did not have preventive applications previously applied in the fall. We are currently conducting a trial evaluating applications made at five-day two-inch soil temperature averages of 45°F, 50°F, 55°F, and 60°F. The 45°F application was made on March 5, and the 50°F application timed a week later on March 12 just prior to the rain. Now we wait for the 55°F and 60°F applications.
We also are applying fungicides in either one gallon of water carrier per 1000 sq ft or two. Many prefer to apply at a single gallon, particularly on larger acreage to cut down on the number of sprayer fillups and mixes. Previous research by Benelli et al. at University of Tennessee has shown, however, that increasing spray volume can increase control since the pathogen infects at the leaf sheath were spray deposition would be most beneficial. We'll continue to test this in relation to spray application timing.
We anticipate relating these findings at the Mizzou Turfgrass Field Day this summer. At this point, we may be holding this field day event in a virtual format as has been delivered around the country in 2020. The advantage is that we are taking photos and videos now of this large patch research, which normally could not be seen in its brilliant color in late July. Stay tuned.