Dry Rot of Wood

(also click here for interesting stuff on woodrot - Hearts of Oak Rotted at Anchor!)

I got an E-mail from a gentleman in Pennsylvania who runs a company specializing in repair and reconstruction of water-damaged or flood-damaged buildings. Goodness knows, with the weather being what it is in recent years this might be a flourishing business.

At any rate he was repairing wood rot damage in a church and observed an interesting phenomenon that he had never seen before.   Associated with the rot was the presence of a fine garnet-coloured dust over large areas of the church and this dust was not confined to the area where the wood rot occurred.

Serpula lacrymans (Dry Rot Fungus) is the only wood rotting fungus that I know of that matches this description.  This fungus is the most serious wood rot in the United Kingdom and also some other European countries. It is not generally regarded, however, as a serious problem in North America except under special conditions.  Although if truth be known it may be a lot more serious than we read about.  In the U.K. Serpula lacrymans causes approximately 400,000,000 worth of damage annually (circa. C$1,000,000,000).  It is also a serious problem in other parts of Europe!

Serpula can attack and rot wood that has become wetted and has a 25% moisture content or higher.  Most important is that Serpula forms hyphal strands called rhizomorphs. These strands are made up of parallel hyphae (fungal threads) that can transport water and nutrients for long distances (many metres).    By means of rhizomorphs the fungus can cross inhospitable territory and even pass through loose mortar or bricks or stone work to establish itself at a new location of unaffected wood.  The Serpula fungus, uses the transported water etc from an established site, to attack dry wood at a new site.  This capability makes it very dangerous and hard to eliminate from affected sites in the UK.

Once established at the new site the fungus digests the wood as an energy source.  Wood is made up of cellulose and lignin.   Cellulose is a carbohydrate and is completely metabolized by the fungus and breaks down into the carbon dioxide and water.

                    Cellulose ---- carbon dioxide + water

Serpula possesses a very impressive capability!   The fungus can  use the water it produces from breaking down the cellulose (metabolic water) for further growth.  Sometimes so much water is produced that the wood drips water droplets.  This ‘weeping’ gives the fungus its species name (= lacrymans).

The rhizomorphs may reach sites that are not suitable for growth and under these conditions will produce large pancake-like or irregularly flat fruit bodies on floors or walls or wherever.  Fruitbodies may be a metre or more across.  They produce red-brown elliptical spores by the billion and these are transported by air currents all over the place. Individually they are microscopic in size but  in billions, however, they will appear as a fine reddish brown dust over surfaces where they are deposited.   In many cases in the UK the first indication of damage by the dry rot fungus is this red dust over the furniture.    It reduces the strength of the wood so dramatically that you can fall through a wall just by leaning against it.   

Why is this fungus not a serious problem in North America?  During the winter in northern NA the hot air heating systems reduce the relative humidity in homes substantially to the point where the wood shrinks.   This drying out of the wood to very low levels of moisture content will eliminate the Serpula fungus.  Or so they say!   Also there is a wide variation in North American climates across the continent. So it could be a problem in some regions but not in others.

Serpula is rarely reported in Southern Ontario where I live.   Although it has been reported from time to time I have only seen it once.   Is Serpula the cause of the problem in the church in Pennsylvania?  The presence of large amounts of 'garnet coloured' dust  suggests this possibility.   So far as we know, however, this is not a common fungus.  Proof would be microscopic analysis to show the dust was actually the spores of this fungus.  If you were on site, however, you could look for the very large, red-brown pancake-like fruitbodies.

So to confirm all this, I asked the company from Pennsylvania to send me a sample of the "dust" he found in the church.    As I write this (Jan. 3rd. 01) the sample has not arrived.    It may take ten days if he sent it by snail mail.   Who knows maybe the Customs will refuse entry!   When it does arrive, however,  I’ll have a look at the dust with a microscope and let you know the result.


January 8th 2001  -   The dust samples, postmark dated 29th December, arrived in my mailbox at U of Guelph on Monday 8th Jan!  So much for the US/CANADA  mail service!   My guess of ten days was pretty close. 

Result:         BINGO!    The red dust proved to be spores.  Under the microscope the spores were red-brown, elliptical and measured about 8 X 6  microns.  This is the colour, shape, and size of the spores in descriptions of Serpula lacrymans.   For fruitbody click here

How to control it?      Check the web!

Wet Rots:

As you know to your cost, if you keep wood wet for long periods in due course it will decay to dust.   I once followed the deterioration of a hardwood log in the Arboretum at Guelph and it was a long slow process.  It took about twenty years after felling and even then  I could still see mounds of woody debris.   Cedar fence posts  if not properly set in concrete will rot away at ground level in 10-15 years.   Make shore the concrete casing is a few inches above ground level to prolong the life of the post.  In homes if  timber is kept wet for prolonged periods it will decay slowly.  Unlike dry rot,  wet rot   is relatively easy to control and  can be stopped in its tracks by drying.     i.e.  dry out the wood and the rot will stop

In the natural system, wood rotting fungi play a most significant part by rotting wood to carbon dioxide and water and returning hundreds of billions of tons of CO2 annually to the atmosphere to fuel the Carbon Cycle.    Remember the fungi are the major players in their role as biodgraders of woody debris (cellulose and lignified cellulose).

More on Brown Rot Fungi and White Rot Fungi later!

Note:Background = chains of Alternaria conidia