SURVEY QUESTION

GOLF: Have you applied a fungicide to greens yet?

Yes a few weeks ago
Planning this week
Planning next week
No

Update (03/27/2017)

Is It March or a Climb?

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Marching Up and Down

  1. Heat/freeze/thaw has been the recipe for March. - Source: Pat Guinan
  2. Much needed rain arrived last week; now when will it stop? - Source: Pat Guinan

Weather

The crazy swings of spring that we all know and love are in full force in this early season.  After record breaking warmth in January and February, an early spike in March temperatures sent trees a bloom and many turf managers scurrying.  As warned in the previous update, if history was our guide another hard frost was in the cards for March, which is exactly what happened on March 14-15 with 14 – 20 F lows in the region. At MU South Farms, the 13.4 degree low on March 15 was the coldest since January 8. Forsythia and particularly Bradford Pear tree flowers shocked to a special shade of orangish – brown, and the budding spring season came to a grinding halt.  The Missouri Frost/Freeze Probabilities Guide is a valuable resource that provides a historical perspective of both spring and fall in the state.  Kudos to our state climatologist Dr. Pat Guinan for creating this tool.

Much needed rain graced the region, with 1 – 2.5” around the state in the last 7 days.  Since January, the region has been devoid of snow cover or rainfall, with deficits ranging from 0.5-1” in northern AR/Springfield to over 3” in the St. Louis area. Good rainfall chances will continue through this week and into early April. Warm weather is also slated to return in April, which will presumably vault soilborne disease prevention onto the to do list.

8-14 Day Outlook: Warmth returns, rain persists

  1. Early April should bring back spring. - Source: NOAA CPS
  2. Consistent rain chances are also on tap for early April. - Source: NOAA CPS

The Early Arrivers

Cool Season Brown Patch & Dollar Spot - First Arrivals

  1. Cool season brown patch hit some bentgrass greens after the March freeze.
  2. Dollar spot also was observed late last week on the heavily inoculated MU disease green.

Cool season brown patch – The recent blast of cool weather shut down bentgrass greens and let cool season brown patch or yellow (caused by Rhizoctonia cerealis) in the door.  A report of the disease came in from Springfield, and on the same day we observed the disease on a few bentgrass collars at the turf farm. The disease causes very little, other than cosmetic, damage and the grass recovers quickly when warm temperatures resume.  For this reason, unless the disease is extremely prevalent, curative controls (azoxystrobin, flutolanil, fludioxonil or propiconazole) are not advised.
Dollar spot – Dollar spot arrived on the extremely infested disease green at the MU turfgrass farm late last week. While noteworthy, and indicative that a preventive application is near necessary, the observation should also be taken with a grain of salt. The green is located in a low spot at the farm and each year this green is inoculated with a heavy load of the dollar spot pathogen. Still, the observation should perk the ears that the time for preventive disease control on greens and zoysiagrass fairways is very nearly upon us.  

Large Patch Prevention – Zoysia Fairways and Lawns

Large Patch: The first few green leaves of zoysiagrass are peaking through prominently now in mid Missouri and according to our recent research the time is ripe for large patch prevention. Last year, we initiated a large trial investigating the impact of spring application timing, post-application irrigation, and fungicide choice on large patch control. Neither post-application irrigation or fungicide made a statistically significant impact on large patch severity, but timing surely did.  Applications made at a threshold of 50 F 5-day average 2” soil had significantly less large patch than plots sprayed later at the 60 F threshold. Fungicides were applied to very dormant zoysia in the earlier timing, and near the second mowing during the later timing.  These results indicate the best timing for prevention is likely now during this rainy period and when the zoysia is slowly greening up.

Soilborne Diseases on Putting Greens  

Nipping the 5-day Soil Temperature Threshold

  1. Springfield soil temperatures have incurred wild swings in the last 3 weeks.
  2. Early this week, Columbia soil temperatures climbed to the threshold but haven’t stayed.
  3. Similar soil temperature trend in Columbia.
  4. KC soil temperatures have been the highest among the four urban centers of late, but are now declining slightly.

If forecasted temperatures hold, 2” soil temperatures should stabilize in the 55 F to 60 F threshold area for much of the region near the end of this week and at least by early April.  In the figure above, average daily 2” soil temperatures (the blue line) peaked in the threshold region a few times in mid-February, early March, and few days ago, but the steady climb of the more important 5-day average (the red line) should reach and maintain in the zone over the next week.  For those aiming to prevent fairy ring and patch diseases like summer patch and take-all patch in the region, the first of two (28 d interval) watered-in applications of a low rate DMI fungicide is advised in the next week.  A few important notes about this preventive strategy are outlined below.

  • Low rates of the demethylation inhibiting (DMI) fungicides have worked well in this management strategy.  Triadimefon (Bayleton), triticonazole (Triton, Trinity), metconazole (Tourney), and tebuconazole (Torque) have been demonstrated as effective.  Combination products with these fungicides should also be effective.     
  • Preventive fungicides must be watered-in with at least 1/8” and preferably 1/4” of post-application irrigation.  Preferably, irrigation should occur immediately afterwards, but our research indicated no loss in fairy ring control if irrigation occurred 10 hours after application.
  • Wetting agents should not be tank-mixed with these preventive applications, but should be made on their regular schedule 14 days after/before the fungicide application.  In a curative situation with fairy ring symptoms present, a wetting agent should always be tank-mixed with the fungicide. 
  • Side effects with DMI fungicide use should be minimized due to utilization of lower rates and a spring application window with minimal heat stress.  Caution should be exercised when using other plant growth regulators such as paclobutrazol (Trimmit, TGR) since they are related to DMI fungicides. 
  • For those with ultradwarf bermudagrass greens with possible winter damage (outside the MO viewing area), I suggest waiting until after full bermudagrass green-up (and winter damage can be assessed) before making a DMI application.
  • As a side benefit, we have also noted substantial reductions in dollar spot activity on creeping bentgrass greens through August in treated plots.  The longest residual dollar spot control was observed in triadimefon and tebuconazole treated plots.  As mentioned above, the environment has been prime for at least some dollar spot pathogen development over the past few weeks, so this is a nice advantage. 
  
Pythium Root Rot: With currently waterlogged soils, my mind also turns to Pythium root rot prevention on bentgrass putting greens. While the DMIs have been proven to work in the above strategy, the chemistry will not have an effect on Pythium infection likely occurring now. On greens with a confirmed, perennial issue with this tough to control disease, a targeted, watered in fungicide application should also be considered soon.  Double dipping with a single application here, as noted with the diseases above, is more difficult since Pythium spp. are not true fungi and are not susceptible to many of the broader range fungicides.  Cyazofamid (Segway) is the heaviest hitter on root disease causing Pythium, but is a one trick pony in this regard.  QoI fungicides, such as Lexicon, Insignia, or Heritage, on the other hand may be the best broad spectrum fungicide that hits some Pythium spp. while also knocking back other fungal soilborne diseases.  For the most disease challenged bentgrass roots, the best program may be a watered in QoI fungicide application targeting Pythium root rot in between the two 28 d interval DMI applications, leaving the first Segway application for just prior to summer’s heat.    

Lee

Lee Miller
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Extension Turfgrass Pathologist
University of Missouri