ZOYSIA: When do you apply preventive fungicides for large patch?

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Update (03/15/2016)

Will Warm Weather = March Madness?

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Warm Early March A.  The first 10 days of March are 5th warmest on record, and nearly 10 degrees above average.  - Source: Pat Guinan   B.  Most portions of the state got ~ an inch of rainfall over the last 7 days, with southern regions receiving nearly 2

The first half of March preempted spring in Missouri (which officially begins March 20) by delivering very spring-like temperatures. This mild weather pattern has been remarkably consistent, as February was slightly more than 4 degrees above normal (warmest since 2012), was the 6th consecutive month with above normal temperatures, and led to a tie for the 7th warmest winter (Dec – Feb) on record.  March 1-10, 2016 was the warmest since 1992, and fifth warmest on record with most regions experiencing 7-9 degree above normal temperatures. Interestingly, the top 5 warmest March 1-10 periods have not translated into the top 5 overall warmest monthly March temperatures (see above).  If this holds, perhaps cooler temperatures are on the way, as also indicated in the NOAA 6-10 day forecast shown below.

A rainy weekend provided most in the region with at least a quarter inch of rainfall and in some southern regions nearer to three quarters.  We narrowly missed the large flooding events that occurred in Texas, Mississippi, Louisiana, southern Arkansas, and western Tennessee.  Some of these areas have received 15-20 inches of rain over the last 7 days, an incredible amount over such a short span.  The mild in comparison rainfall and warm temperatures in our region prompted the emergence of many weeds, with knotweed most prominent now alongside our campus sidewalks.  The rainfall/temperature combination has also got the cool season turfgrasses growing well now, particularly some bluegrass in my lawn that will soon require a blade.       

6-10 Day Outlook: Cool Down Expected A.  Temperatures are expected to dip towards the end of the week. - Source: NOAA CPS B.  Drier skies are anticipated along with the cooler temperatures.  - Source: NOAA CPS

A Quick Hit

  • Weed Emergence/Preemergents: The forsythia and daffodils are officially blooming in mid-Missouri now, which means we are in the optimal timing window for crabgrass preemergents to be applied.  According to the GDD tracker ( and most forsythia in the state, Missouri is in the optimum range for application with 250-500 base 32 GDDs.  Looking back on previous years in the system, we are about 2-3 weeks ahead of schedule with GDD accumulation.  I discussed this topic with Brad Fresenburg, and he too believes we are in the window for application, and no resetting freezing temperatures seem to be in the forecast.  He also stated that if any year was built for a split application strategy this would be the one.  So apply half rate now, and come back 6-8 weeks later and put down the other half… the layaway program for warm season annual grass control. 

Part II: Spring Application Timing: Planning

Current Soil Temperatures:  Daily 2” soil temperatures have breached 55 F several times in the last few days, but the 5-d average has just touched the 55-60 F threshold.

At this point, spring has started to show its cards with a considerable tendency towards coming out of the gate early.  Most regions in Missouri have eclipsed the 55 F mark for average daily soil temperature.  Because of this, I was posed an interesting question last week –

“According to my sources, the soil temperature has reached 55 degrees F.  My aerification is scheduled for March 21 on my Crenshaw putting greens.  Should I apply the preventive DMI application for fairy ring on Monday, and aerify the 21st, or wait to make the application until after the aerification?  Will I miss the window?”

I’ve fielded similar questions to this, but the previous didn’t lay out this scenario and all of its necessary considerations. First, the soil temperature threshold for the preventive fairy ring application is based on a 5-day average taken at 2 inches.  This broad average over several days mellows out the wide swings in spring temperatures that often occur in Missouri and the rest of the transition zone.  Note the average daily temperature (shown as the blue line in the above graphs) wildly varies, while the 5-day average (shown as the red line) is not as prone to the immediate peaks and valleys.  Also note, that over the past weekend in Springfield, Columbia, and KC even the red line (5-day average) hits 55 F. 

In this case, the 55 F line is not a magical threshold, however.  Note a range is indicated in the graph above from 55 – 60 F.  The first application should be targeted within this zone, which gives the superintendent a bit of leeway on how quickly to hop on the sprayer.  When initially reached this early in the spring (or late winter depending on your definition), the 55 F 5-day average soil temperature should require one to check the forecast.  Are temperatures slated to remain the same or increase?  If so, the spray should be planned over the next few days, and a third application in May may be necessary.  If air temperatures are slated to decrease and drive the soil temperature back out of the zone, then lay off the spray and reevaluate when the next warmup occurs.    

Another important aspect of this scenario is the timing of the aerification event.  Although reduced rates of DMI fungicides are used in a similar method to the split application strategy for crabgrass preemerge, there is still some risk for plant growth regulator effects from the lower DMI rates.  Previous studies have demonstrated a 7-14 day reduction in recovery from aerification on plots treated with some DMI fungicides compared to non-DMI treated plots.  Some variation occurs in this observation among different cultivars or post-aerification fertilizer regimes, but why take this chance if its not necessary?  An open aerification hole is an invitation for Poa, so closing them up ASAP should be a priority.

The last consideration has to do with another disease breathing down our neck: dollar spot.  Our research has demonstrated some dollar spot control with the watered-in preventive applications, particularly when either triadimefon or tebuconazole was used.  Note the greens are ‘Crenshaw’, a cultivar particularly susceptible to dollar spot, which increases the potential for an early outbreak.

In conclusion, I suggested the superintendent wait until after the aerification was complete and the greens were healed. The 55 – 60 F soil temperature threshold has been barely pricked, and the forecast indicates a fall in temperatures that will drag it back out of the zone.  Also, if the first preventive application is made too early, the second “split” application 28 days later will also be potentially too early, requiring a third application.  In addition, the risk of the DMI application limiting aerification recovery is considerable. I did recommend the superintendent scout intensely for dollar spot, and respond quickly with a curative application if needed.  

Lee Miller
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Extension Turfgrass Pathologist
University of Missouri