Snow Moulds

Arthur Pelegrin of Washington State sent me JPEGs of several fungi and lichens.  The one below was possibly the best and is very appropriate as a topic for this month's special.

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The picture shows young sclerotia of a Typhula species scattered over the surface of a winged seed (samara) of a Maple tree.   Sclerotia (singular = sclerotium) are hard, multicellular, fungal structures for long term persistence over adverse conditions.  Large by fungal standards, sclerotia  carry stored energy into the next growing phase.  This allows the fungus a fast and/or aggressive start in the new season.   In the case of Snow Moulds the new growing season starts with the snow cover in early winter!    Sclerotia are particularly common in parasitic fungi and  snow moulds just love grass as a host.    If you are a keen golfer then you are very familiar with snow moulds.  These are the fungi that cause the unsightly patches of dead grass on the greens that you see after the snow melts in the spring.   In the high mountain valleys that are becoming favourite locales for new golf course development, there is prolonged snow cover and snow moulds attack both greens and fairways in such regions with devastating results.   They often cause a complete wipeout i.e. no green grass at all after the snow melt.

Sclerotia allow the fungus to survive adverse conditions such as drought or heat.  The adverse condition for snow moulds, however, is the growing season for most others ( i.e. spring, summer, and fall).  Snow moulds are cryophilic (cold lovers);  they grow happily and attack their host at 5C (about the temperature of a refrigerator).   BUT -  as you know air temperatures in winter are often more like a freezer.  HOWEVER - the blanket of snow over the grass acts as insulation.   Also, the sun penetrates through the snow and raises the temperature at grass level.  SO - for much of the winter the day temperature at grass level under snow is above freezing and is perfectly fine for snow mould growth.  The longer the snow cover the more fungal growth and the greater the damage.  In our region (Southern Ontario) it takes at least 90 days of snow cover before serious symptoms start to develop.   So, the intensity of the disease varies considerably from year to year according to snow fall duration and region. 

In the northern U.S. and Canada, Snow Moulds cause sleepless nights for golf superintendants and perhaps even give them nightmares.  The current control for this group of diseases is to pour on chemical fungicides.   The levels of pesticides poured on golf courses across North America to control insects weeds and fungi is staggering and this solution to the problem is becoming  less and less environmentally acceptable.   So, golf courses would be a good place to initiate serious attempts at biological control.   

Biological Control

All is not lost!   It just so happens by sheer coincidence that Dr. Tom Hsiang (pronounced Shung) is working at the University of Guelph on this very problem and just along the hall from me!   This is the same Tom Hsiang who I acknowledge in my book for his invaluable assistance in keeping me on the computer track despite my many lapses and transgressions.  

Basically Tom is using one innocuous fungus, Typhula phacorrhiza, to suppress a disease called Grey Snow Mould caused by the related parasitic fungi Typhula ishikariensis and/or Typhula incarnata

I have seen promises from many who are going to solve the pesticide problems of the world using biological control methods.  But, if truth be told,  there have been very few successes.  Sometimes they just don't work at all.  Sometimes they don't effect a high enough level of control.  The final product may me outrageously expensive or often the method and timing of application of the control agent is too complex to be practical.  Thus, for one reason or another there are many failures in biological control technology.   Even when they work it is not always according to plan as biologcal agents are themselves influenced dramatically by environmental conditions.  All in all, biological control is a hit or miss affair in most cases.

That being said you see from his webpage that Tom Hsiang has had some very promising results in his biological control experiments on Grey Snow Mould.     Indeed, some results verge on the spectacular as you see from his photo (click here).

So if you are really fascinated by Snow Moulds then check out the details at Tom's website. See   And if you are really, really, really fascinated by Snow Moulds check out the amazing antifreeze proteins produced by cryophilic fungi, and other organisms, to prevent ice crystal damage at freezing temperatures (also on Tom's website).


1.  Define the term 'sclerotium'.  Don't give mine - improve on it.

2. The 'ergot' in ergot of rye is the sclerotium of Claviceps purpurea, the causal agent of this disease.  Explain the importance of the sclerotium in the life cycle of this fungus (hint - stromata, primary inoculum, rye flowers and all that stuff!)

3.  Give two other examples of sclerotia in fungi and suggest why they are important to the fungus.  Remember a sclerotium is a big investment of resources for the fungus and this committment cannot be made lightly i.e. there should be a biological advantage.

4.  How long can a sclerotium survive - i.e. months, years, decades?

5.  How do sclerotia prevent biodeterioration (predation) by other organisms in the soil and what influence might this have on non target organisms.    (hint - check out  St. Athony's Fire)

6.  Sclerotia are often darkly pigmented what pigment is involved and what is its function.

7.  Many dematiaceous Hyphomycetes (e.g. Alternaria, Cladosporium, Drechslera) and mushrooms (e.g Agaricus, Panaeolina, Coprinus ) have this same pigment in their conidia.  Explain its possible purpose and function in these fungi.  If it's so good why don't all fungi have it.