Dry rot

  Dry rot would appear to be an oxymoronic term seemingly indicating decay of a substance without the presence of water. However, its historical usage dates back to the distinction between decay of cured wood in construction, i.e. dry wood, versus decay of wood in living or newly felled trees, i.e. wet wood^[1]. The term has been applied to the decay of timber in buildings and other wooden structures by certain fungi, the decay of crop plants by fungi and the deterioration of rubber. In addition, the term can be used as a metaphor for grave underlying problems within a large organization (such as political corruption in government or low morale in the armed forces) that show no symptoms until a sudden, catastrophic failure, much as dry rot of wood in ships caused catastrophic failure.

The term is most commonly used in reference to the decay of building timbers. It refers to damage inflicted by either: Serpula lacrymans (formerly Merulius lacrymans) predominantly in the United Kingdom and northern Europe; and/or Meruliporia incrassata (which has a number of synonyms, including Poria incrassata and Serpula incrassata) in North America. Both species of fungus cause brown rot decay, preferentially removing cellulose and hemicellulose from the timber leaving a brittle matrix of modified lignin. Eventually the decay can cause instability and collapse in houses, wooden ships' hulls, and other wooden structures.

When applied to these fungi, the term is a somewhat misleading misnomer as both species require an elevated moisture content to initiate an attack on timber (28-30%). Once established, the fungi can remain active in timber with a moisture content over 20% - in the same way as other timber decay fungi using the brown rot decay mechanism.

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Historical use of term

‘Dry rot’ is an eighteenth century term for a brown rot. The term was used because the damage was thought to be caused by internal ‘fermentations’ rather than water.

The (London) Times on Tuesday, March 12, 1793 carried an advertisement that informs the reader that THE BRITISH COLOUR COMPANY, No. 32, Walbrook, London continues to use, manufacture and sell paints prepared with the Oil of Coal, which is of a very penetrating nature, and hardens wood in an uncommon degree protecting it from weather, dry rot and ice.

In the early nineteenth century the rapid increase in instances of timber decay attributed to dry rot (brown rot) in the British naval fleet brought the term into wider usage. The second HMS Queen Charlotte was launched in 1810 and, when inspected, the timbers of the upper decks were found to be infected with 'the dry rot'. A. Bowden of the Navy Office published 'A Treatise on the Dry-Rot' in 1815 following his investigation of the matter.

Texts published in the nineteenth century and early twentieth centuries restrict the term to fungi which produced substantial (white coloured) mycelium including; Antrodia (Fibroporia) viallantii. Eventually, the term came to apply to only one or two fungi: the main one being Serpula lacrymans, which subsequently became known as 'true dry rot'.

Schilling & Jellison^[2] define dry rot fungi as: "a specific group of brown rot fungi that efficiently translocate water via mycelial cords." They cite M. incrassata, S. himantoides and S. lacrymans as dry rot fungi. There is no reference for how efficient a brown rot fungus has to be at translocating water in order to be classed a 'dry rot'. Water translocated in this fashion carries nutrients to the extremities of the organism; not, as is sometimes inferred, to render dry timber wet enough to attack. Coggins^[3] goes into more detail about water movement in S. lacrymans.

Treatment (of timber decay fungi identified as 'dry rot')

There are epoxy treatments available that kill rot by filling in the channels of the damaged wood, killing the rot and restoring structural integrity. Commercial anti-freeze is also very effective at preventing dry rot formation as well as killing the fungus.

References

See also

• Wet rot
• Brown rot of fruits
• White rot