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Update (4/2/2013)

The Thresholds Are Coming!!!

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March weather cooler than normal.

March turned out to be cold and wet, with the last half of the month bringing a little rain and a good deal of snow from “Virgil”.  High temperatures for much of the last two weeks were on par with the average low temperatures for the region, as a dipping jet stream sped storm systems across mid Missouri.  As I’ve heard commented a few times over the last few weeks, “Punxsutawney Phil got it dead wrong this year.”

Cool temperatures are forecasted to stay for the first few days of April, but rise to approximate normal temperatures this weekend and stay there over the extended 10-day.  The 30-day April forecast has the southern half of the state with warmer than normal temperatures, and average temperatures for the rest of the state.  So, it’s fairly safe to say that spring is now set to arrive, and the season has officially begun. 

Over the course of the next few days, soil temperatures (2”) should be recovering to around average for this time of year.  Of course, this has implications for timing of pre-emergent herbicide and preventive fungicide applications (see below).  Aerification of cool season turf is also occurring en masse throughout the region, and the rising soil temperatures should encourage a quick recovery.

Soil temperatures for Missouri are starting to rise this spring.

Quick Hits            

  • Step one: Calibration.  If you haven’t yet, it’s time to calibrate those sprayers before applying pesticides.  Dr. Brad Fresenburg from MU wrote a fantastic article last week detailing the use of the 128th rule for calibration (click here to read the article).  It’s simple and effective, and the best part is that once the initial work is done, you can check your nozzle output quickly throughout the season. 
  • Step two: Weather monitoring.  It’s all about using your resources.  Aside from the normal weather sites, I also utilize the Horizon Point Site-Specific Weather System, which is targeted for row agriculture, but gives a good idea of the current weather conditions.  Of these, I really key in on the 2” soil temperature data (as pictured above) that is provided every day via email if you sign up for the free service.  Another great resource is the Growing Degree Day Tracker (  This system does all of the dirty work of calculating degree days for predicting weed germination/seeding and pre-emergent application timing.  Additionally, it also incorporates forecasted data so management practices can be planned more effectively. At this time, however, Illinois is the closest state participating in gddtracker, so those in the eastern portion of the state can derive the most benefit from this service.

Step 3: Mind the Thresholds

Timing preventive pesticide applications is tricky.   The target pest is difficult to detect due to low pest populations and a lack of turfgrass symptoms to substantiate pest presence.  There are some pests like crabgrass or Poa seedheads that we know will occur, and there are others like fairy ring or patch diseases that we know occur based on previous site history.  For these, getting ahead of these pest epidemics is often necessary to achieve good control.  See the table below for the most common thresholds used in preventive application timing.       

Thresholds for some of the most common preventive pesticide applications.

Current Threshold Status

Crabgrass: The target range for applying pre-emergent herbicide applications or corn meal gluten meal should be on southern MO this week, and early into the next week for central MO.  If you are going for split applications, apply this first one now, and the second application 6-8 weeks later.  Also if the herbicide is applied with a urea carrier, it is best to apply the herbicide + fertilizer now and leave the second split application as herbicide alone (click here for reasoning).  If you are going to be tardy, dithiopyr (Dimension) has some post emergent control on smaller crabgrass plants.

Poa annua seedhead control:   Poa annua seedheads can be bothersome on putting greens with high infestations.  In previous studies, a tank-mix of Proxy (5 fl oz per 1000 sq ft) and Primo (0.125 fl oz per 1000 sq ft) provided suppression when applied just prior to seedhead appearance (~ 50 – 100 DD50 or 220-320 DD32).  In the northern U.S., two applications are necessary 21 days apart to catch the second flush of seedheads.  Currently, St. Louis sits right around 200 DD32, so the first application should be made in that region late this week or early next week.   There is a report in St. Louis that seedheads are starting to appear bordering hotter surfaces such as cart paths, indicating the timing is getting close. 

Fairy Ring:  We are still about a week away from spraying preventive fungicides for fairy ring control on putting greens.  The key with this threshold is that mean 2” soil temperatures should average  55-60 F over 5 days.  In native soils, average soil temperature in the Bootheel was 53 F, with St. Louis at 49 F and Kansas City at 45 F.  If the warming trend continues, I anticipate the first application should be made late next week or early the week of April 15th.  But stay tuned.        

Happy Spring! 

Lee Miller
Follow on Twitter!  @muturfpath
Extension Turfgrass Pathologist
University of Missouri 


Link to preventive application information for fairy ring control.