February 15, 2011

University of Arkansas, Division of Agriculture

Turfgrass Science Program (http://turf.uark.edu) – Turf Tips

Beware of Microdochium Patch

It is not often that we have to enlist the help of a turfgrass pathologist from Wisconsin to help with Arkansas disease problems, but this year's winter is starting to resemble a Wisconsin winter across much of the state, with record low temperatures and record snowfall. Earlier this winter, a disease sample was submitted to us from the Hot Springs area and the pathogen was confirmed as Microdochium nivale. This is the causal organism of Microdochium patch (Fig. 1), which was present even though there had been a minimal amount of snowfall at that time. We also observed significant Microdochium patch in one of our bentgrass cultivar trials last spring after approximately 30+ inches of snowfall in the winter of 2009-10. The results of that study were published in Applied Turfgrass Science (http://www.plantmanagementnetwork.org/ats/element/sum.aspx?id=9293&photo=5098).


Fig. 1. Symptoms observed in Hot Springs, AR following minor snow event in January 2011.

Based on these observations, golf course superintendents should be aware that Microdochium patch may become evident on creeping bentgrass putting greens throughout Arkansas following snow melt. This disease has been referred to as fusarium patch or pink snow mold in the past. Microdochium patch does not require snow cover, but the freeze/thaw cycles and increased moisture due to snow melt combined with moderate temperatures may produce environmental conditions favorable for disease to occur. With the current conditions, the development of Microdochium patch may be alarming.

The symptoms of Microdochium patch (see Fig. 2) include circular patches that can expand to 8 inch diameter. Initially, patches will be much smaller (approx. 2 in. diameter) with a water soaked appearance. The affected area will continue to increase as long as humidity remains high under cloud cover and moderate temperatures. As snow continues to melt and sunlight begins reaching the infected area, the fungus will produce many spores that create an orange to pink coloration near the outside border of the patch.

Fig. 2. Initial symptoms are going to be small and appear water soaked (left). If environmental conditions remain favorable for disease development, patches will enlarge and join together. Increased spore production would give the patch an orange to pink coloration (center). If spore production is minimal, you may only see white mycelium produced (right). We thank Dr. John Kaminski for providing these images. More images of Microdochium patch symptoms and signs can be viewed at Dr. Kaminski's Flickr page: http://www.flickr.com/photos/johnekaminski/sets/72157622014051512/with/3812254997/

Microdochium patch is not a common disease observed in the southeast during the winter months; therefore, most superintendents in our region do not make preventative fungicide applications. Based on the extended period of snow cover we recently experienced in Northwest Arkansas and throughout various portions of the state, we are recommending that fungicide applications be made following snow melt and IF air temperatures remain below 68 degrees F with high humidity, intense cloud cover or both. There are two things to keep in mind when deciding to apply a fungicide for clean up of Microdochium patch: 1) is the fungus active and 2) applying fungicides to saturated ground should be avoided entirely. Although the disease may appear to be severe, it may not be initiating new infections because of a non-conducive environment. Additionally running a sprayer over saturated ground will likely cause more harm than the fungus itself, plus there is serious potential for losing the pesticide in the form of runoff. If you are unsure about whether to spray or not, consult your local turfgrass extension specialist or diagnostician. The list below only discusses active ingredients and does not include the wide variety of fungicides that have two or three active ingredients.


Table 1. Fungicide active ingredients that control Microdochium patch well. The listing order of the active ingredients listed below is from the most efficacious to least. Chlorothalonil is a great product to use in a tank mixture with respect to Microdochium patch control.

Fungicide Active Ingredient

FRAC Group

Fungi Controlled

Iprodione/Vincozolin

Dicarboximide

Microdochium

Thiophanate methyl

Benzimidazole

*Microdochium; **T. incarnata

Trifloyxstrobin, Azoxystrobin, Pyraclostrobin

Strobulurin

Microdochium; T. incarnata

Chlorothalonil

Morpoline

Microdochium; T. incarnata

* Microdochium is the fungus causing Microdochium patch, pink snow mold, or fusarium patch.
** T. Incarnate is the fungus that causes gray snow mold.

Joey Young (PhD Student) and Dr. Jim Kerns (Univ. of Wisconsin)

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