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Update (2/18/2011)

2011 Winter Disease Report

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To say the weather pattern has been erratic over the past week is to put it mildly.  Record lows were recorded on February 10, and potential record highs are being set throughout the state today.  This has led to a fast snow melt, and golf courses opening during this period will need to severely restrict cart traffic.   The native soil green at the Turf Farm was still saturated yesterday and would be deemed unplayable, (and as you’ll read later unsprayable).  Sand-based greens are damp but in fairly good shape.   

The (pathological?) minds of turfgrass pathologists must think alike, as several snow mold alerts have occurred throughout the Midwest in the last two days.  I am no different; as soon as I can see blades of green the disease scouting eyes sheen.  The MU turf pathology team scoured the Turf Farm heavily for signs of two diseases, snow molds and cool weather brown patch, which can be active under snow cover. Unfortunate only to us pathologists, we found nothing.  However, gray and cottony snow molds have been seen in Columbia, and cool weather brown patch has been reported in St. Louis.

Snow Mold

Gray Snow Mold & Cottony Snow Mold

Gray snow mold/Typhula blight and cottony snow mold/Coprinus snow mold have been observed on several higher cut Kentucky bluegrass and mix bluegrass/fescue lawns and sports fields that were not treated with preventive fungicides.  No symptoms of these snow molds have been reported from golf course areas. 

Gray snow mold appears as light yellow, or straw colored patches from 1 inch to 3 feet in diameter (Fig. 1A).  Cottony snow mold is being observed as conspicuous tufts of mycelium 2-4 inches in diameter (Fig. 1B).  Of the areas seen thus far, only the turf leaves are being killed, meaning regrowth from crowns and stolons should heal these areas quickly when temperatures rise.  However, in higher amenity areas such as sports fields and golf greens and tees, a curative fungicide application may be warranted (see below).

Disease Picture

Pink Snow Mold/Microdochium Patch 

Of the varying types, pink snow mold is much more prevalent in Missouri, with gray, cottony, or speckled snow molds occurring in years like this one with more extended snow cover.  Pink snow mold is the phase of the disease that occurs under snow cover, but the disease can also be very active in cool, wet weather in the spring when it is referred to as Microdochium patch.  These two disease phases caused by the fungus Microdochium nivale are often more severe than other snow molds because the pathogen often infects the crowns of the plant.      

The disease can occur and damage nearly all cool-season grass species, but is most severe on Poa annua and creeping bentgrass.  Pink snow mold symptoms often occur as patches that can be 4-8 inches in diameter or larger.  Microdochium patch symptoms are more often observed as smaller reddish brown spots or patches that may resemble Pythium streaking due to the dispersal of conidia by traffic or water.  In conducive environments, pink-salmon colored sporodochia (which produce the conidia) can be observed on leaf sheaths (see Figure 2).

Snow Mold Control

For turf maintained at heights over one inch, it is important in the fall to mow as long as the grass is actively growing to avoid matted turf and a conducive microenvironment.   Nitrogen applications too late in the fall greatly increase disease severity.  In diseased areas, resume spring maintenance as soon as possible and lightly rake affected turf areas to break apart the matted layer and allow turf drying.  Like some other diseases such as take-all patch and summer patch, maintaining a low soil pH can also help suppress pink snow mold.     

Chemical control is often necessary in lower mown, high amenity areas.  Preventive fall fungicide applications are needed with possible re-application necessary in curative situations or during periods of snowmelt.  PCNB is not available and would not be recommended now anyway due to phytotoxicity issues on actively growing bentgrass.  Thiophanate-methyl and the dicarboximides (vinclozolin or iprodione) mixed with chlorothalonil is a good economical solution for curative gray and pink snow mold treatment.  However, allow the turf to dry and never apply fungicides to saturated turf no matter how much disease is apparent.  Runoff may reduce fungicide efficacy, and the traffic may do more harm than good.

Yellow Patch

Yellow Patch/Cool-Season Brown Patch

Yellow patch, or cool-season brown patch, is caused by Rhizoctonia cerealis, a kissing cousin of R. solani, the causal agent of brown patch in the summer.  It has another cousin in Rhizoctonia zeae, which tag teams with R. solani when temperatures get > 90°F.  Yet another cousin is Waitea circinata, which causes brown ring patch (or Waitea patch).  This disease normally occurs later in the spring than yellow patch and is preferential to Poa annua.  Within this large family tree, R. solani’s twin brother also causes large patch of zoysia.  Confused yet?  So are researchers, who are continually trying to properly identify and characterize this myriad of closely related pathogen/diseases.

Yellow patch symptoms appear as yellow or brownish rings or arcs primarily on golf putting greens and collars after snow melt or during periods of optimal temperatures in early spring or occasionally late fall (see Figure 3).  Optimal temperatures for disease development are between 50-65°F, with development ceasing when temperatures drop below 45°F or go above 75°F.

Several fungicides are labeled for yellow patch control, but are seldom recommended because the disease is primarily cosmetic and is short-lived.  If the disease is chronic and fungicide control is necessary, azoxystrobin, flutolanil, fludioxinil, or propiconazole are suggested.             

Prevention Now?  

So what about applying fungicides preventively now on greens if no symptoms are present?  This is a valid question, and one that needs some historical perspective. I am lucky to have Dr. Pat Guinan, the Missouri Weather Man, right across the hall and he supplied some information on the relative probabilities of another snowfall event this spring.  Forecasts show a minor likelihood of snow towards February’s end, but it is not solid and definitely not to be considered a significant event.  Historically, March snow events in Columbia, MO have occurred an average of 76% of the time in the last 111 years, and April has had a snow event only 25% of the time. 

The total snow amount is also important, as March averages 3.7 inches total, and April averages only a half an inch.  This means that if snow does occur again this late winter/early spring it is most likely to thaw quickly, and there will be an opportunity to scout for cool-season disease occurrence and act quickly if needed. Until temperatures steady into a spring pattern, and more turf pathogens start to come out of dormancy, the bottom line is if the greens are clean, just scout them mean.

For diagnostic assistance of snow mold type, yellow patch, or other maladies, feel free to contact me at turfpath@missouri.edu

Also, for more information please see the two recent reports from colleagues in the Midwest:

Turf Disease Blog:  This is a great resource if you have not seen it before.  I recommend signing up for the email alerts of newly posted material.

Arkansas Turf Tips  

Lee Miller
Extension Turfgrass Pathologist
University of Missouri