LAWNCARE: Do you apply nitrogen in June - August?

Only on warm season turf
Every month

Update (05/27/2015)

ETRIs on the Attack

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Cool May Rains A.  A stark cool down later in the month contrasted the early May warmth.   - Source: Pat Guinan   B.  Over the last 14 days, the west has been wet, with well above average rainfall.   - Source: NOAA


In contrast to the warm beginning, the middle portion of May was relatively mild and sometimes even downright cold.  This brought warm season turfgrass growth back down to spring reality, and along with the frequent rains reignited large patch outbreaks in the region.  As is often the case in May (the state’s wettest month at ~ 5”), Missouri has been on the border of colliding fronts and tropical air masses from the Gulf.  Thus far, mid-Missouri has observed average rainfall, St. Louis below average (-1”), and KC and western parts of the state well above average.  Joplin is currently 4.18” above normal for May and the Kansas City area ranges from 2.9 – 5.3” above normal.  The saturated soils have provided prime large patch weather, and as stated in the previous update have set the stage for widespread disease events if high temperatures occur in early June.   

Over the short term forecast, temperatures are expected to be above normal over the next 6 – 14 days (click here for NOAA CPC).  Later next week, temperatures could reach into the 90s, particularly in southern regions of the state and in the urban areas of St. Louis and Kansas City.  If this occurs, and the storms remain frequent, watch out for our first blast of high temperature diseases such as Pythium and brown patch.  Also, sneaky soilborne diseases such as take-all patch or Pythium root diseases may rear their ugly head on bentgrass putting greens.  Make sure you are well vented and well protected. 
Summer weather prognostications are out, and it seems there is some agreement between popular outlets and the more conservative NOAA outlook (below).  Missouri and the surrounding region is slated to be cooler than normal.  The forecasts echo the strong El Niño in the Pacific, and observations in previous summers (1982 & 1997) of cooler Midwest temperatures associated with it.  We are also expected to receive above average rainfall, so if high temperature events do sporadically occur enough moisture may be there to drive disease events.

Summer Outlook from NOAA June - August forecasts indicate a cooler than normal summer for the region (A) and the continuation of our wet weather trend (B).  - NOAA CPS

Quick Hits

Four Diseases in Two Photos A.  ‘Riviera’ bermudagrass with severe spring dead spot (yellow arrow) and large patch (orange arrow). B.  ‘Meyer’ zoysiagrass with large patch (orange arrow) and smaller dollar spots (red arrows).

  • A confluence of warm-season turfgrass diseases is currently occurring throughout the region.  In Columbia, spring dead spot and large patch are being observed on the same area on bermudagrass, and large patch and dollar spot are being observed on the same zoysiagrass sward.  This is a tough time of year for both species as they try to emerge from dormancy and get the juices flowing.  Add on the plentiful rainfall occurring in many parts of Missouri, and these diseases are happy to oblige.  At this point, the damage is done for spring dead spot.  Diseased areas should be mapped for targeted action this fall and fertilized to promote recovery.  Active large patch infections should be hit with a fungicide; granular formulations may be necessary in soggy conditions.  Dollar spot on zoysia or bermudagrass is a clear sign of hunger, which is common on many turfgrass species in areas hit with frequent heavy rains.  No research evidence exists that large patch severity increases with spring nitrogen applications, so you may speed recovery of both diseases with a shot of N now.

Brown Patch Lesions  Upon close inspection, brown patch lesions are occurring on tall fescue in mid Missouri.

  • Brown patch lesions may be found lurking on tall fescue leaf blades if you dig a little.  This is especially true in shaded areas that allow for a longer leaf wetness period.  Higher temperatures slated for late next week may spur these lesions into full-blown patches.  In high amenity areas with a history of infection, consider making a preventive fungicide application now if these lesions are apparent.  Also, in contrast to the above warm-season turfgrass fertilizer recommendation, do not apply nitrogen to tall fescue now.  Nitrogen acts as an “enabler” for troublesome high temperature diseases such as brown patch and Pythium blight, so let your tall fescue stay lean and mean going into this summer’s prize fight. 
  • Dollar spot is still raging through May.  The disease is attacking not only creeping bentgrass, but now is also prevalent on Kentucky bluegrass, Kentucky bluegrass/tall fescue mixtures, and the aforementioned zoysiagrass.  Frequent rains and perfect growth conditions may have depleted nitrogen stores in the soil.  In this case, it’s important to know your host.  If managing primarily Kentucky bluegrass, a small shot of nitrogen (0.25 lb N/1000 sq ft or less) in either a foliar or with a slow-release form may encourage dollar spot recovery.  Although we do observe it on occasion, tall fescue is much less susceptible to dollar spot, and the disease attacking may instead be brown patch… which would be spurred on by the kick of nitrogen. 

  • In areas that have experienced heavy rainfall, be wary of algae infestation on bentgrass putting greens. Algae or cyanobacteria can cause bright yellow, chlorotic spots or blanket infest open areas. If an outbreak occurs, a tank-mix of mancozeb and Daconil in the Ultrex, Zn, or Weatherstik formulation are recommended for control.

ETRI Diseases on the Attack

ETRI Diseases on the Rise A & B : Take-all patch of creeping bentgrass is more apparent on newly renovated greens. The pathogen infects at approximately 55F 2” soil temperature.  C & D : Summer patch is a serious disease on Kentucky bluegrass.  The pathog

Over the past two weeks, take-all patch and summer patch were diagnosed on creeping bentgrass and Kentucky bluegrass samples, respectively.indicating a perfect saturated environment for infection and occurrence.  Both diseases are caused by a class of root-infecting soilborne pathogens termed ETRI or EctoTrophic Root-Infecting fungi.  Recent saturated soil conditions have created a perfect environment for infection and occurrence of these two diseases.        

Take-all patch was observed on ‘V8’ creeping bentgrass green in western IL, which had been renovated 2 years ago via fumigation.  As in this case, take-all patch is often more prominent and damaging on newer putting greens, particularly after methyl bromide fumigation.  The pathogen (Gaeummanomyces graminis var. avenae) is ubiquitous and found in most bentgrass samples, however, it is normally not the main inciter of root decline in older greens.  The pathogen infection period begins at a 2” soil temperature ~ 55°F, with symptoms occurring in mid to late spring.     
The summer patch pathogen (Magnaporthe poae) was observed last week on roots and rhizomes of a pure Kentucky bluegrass stand severely damaged the previous summer.  When established, summer patch can be the most troublesome disease of Kentucky bluegrass, because the pathogen is soilborne and therefore diagnosis and treatment is difficult.  The infection period for summer patch occurs in the spring when 2” soil temperatures ~ 65°F, with symptoms first occurring during early heat events in early summer.

If damage from either of these diseases is problematic, a few common cultural practices are suggested for control.  During the spring infection period, reduce or eliminate use of nitrate forms of nitrogen, and replace with ammonium forms.  Both of these diseases are reduced when rhizosphere (i.e. soil influenced by root) pH is reduced.  Rhizosphere pH is reduced when roots uptake ammonium ions, and is raised when roots uptake nitrate ions.  The pH effect may also be related to an interesting side story involving the micronutrient manganese (Mn).  Some ETRI fungi have been shown to convert manganese to a plant unavailable form during the infection process, rendering the plant host more susceptible.  Manganese is more readily available at lower pHs, so ammonium ion uptake may circumvent the deficiency.  Manganese sulfate applied at 2 lb/A and watered-in during the infection period has also been shown to reduce symptoms. 

If fungicide use is necessary, it should be integrated with the cultural practices noted above.  Preventive applications should be planned when 2” soil temperatures reach 50-55°F in spring for take-all patch, or 65°F for summer patch.  These applications need to be watered-in with at least 1/8” (preferably 1/4") of irrigation to deliver the fungicide to the root zone.  Two – three applications may be necessary on a 21-28 day schedule to achieve satisfactory control.   In a curative situation, recovery is difficult.  Fungicides should be accompanied with 0.2 lb N/1000 sq ft of ammonium sulfate to encourage recovery. 

Mizzou Field Day & Lobenstein Golf Tournament – July 21, 2015 

Fine Fescue NTEP Trial at MU Fine fescues are being used at Chambers Bay, the site of the U.S. Open in June.  At MU, we are evaluating the suitability of their use in MO.

Mark your calendars for the 2015 Mizzou Turfgrass and Ornamental Field Day to be held at the MU Turfgrass Research Farm in Columbia, MO.  We expect to have a morning packed of education on topics ranging from turfgrass pest control to NTEP cultivar trials to ornamental flower selection to soil testing analysis.  In the afternoon, we will be having our first annual Lobenstein Scholarship Tournament.  This 9-hole event will be held at Columbia Country Club and all proceeds will benefit the Lobenstein Fund.  The fund awards two $1,000 scholarships annually to deserving MU undergraduate students in Landscape Design, Horticulture, or Turfgrass Science, and is the legacy of Dr. Bill Lobenstein, who founded the MU turfgrass program and was instrumental in its development.  The forecast for the day is certain to be cool, so plan on a day full of education and camaraderie on July 21.  Registration and other details are coming soon.


Lee Miller
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Extension Turfgrass Pathologist
University of Missouri