Mold and Cell Walls

[Jim Katen]

Many years ago, at a seminar, the speaker (might have been Nathan Yost, but I could be wrong) said something that I have never heard confirmed and that I've since wondered about. He said that the fungi that we commonly call molds are incapable of penetrating a plant's cell walls. As a consequence, molds will only consume those parts of the wood where the cell walls have been sheared off by a saw cut or by other damage. Because of this, molds will not cause much damage to solid wood but can do lots of damage to engineered wood where the wood cells have been cut, pounded, squished and otherwise molested to make them more palatable to molds.

This assertion seems plausible, though I suspect that there might be exceptions.

In contrast, I was recently treated to a presentation by a local mold "inspector" who said that mold fungi consume the wood that they grow on and, if they're not removed, they can cause structural failure. This statement conflicts with my experience. In my opinion, if a moldy piece of wood has failed, it's because it's also infected with rot fungi.

What does current science tell us about molds' ability to consume wood?

- Jim Katen, Oregon

[SonOfSwamp]

Many years ago, at a seminar, the speaker (might have been Nathan Yost, but I could be wrong) said something that I have never heard confirmed and that I've since wondered about. He said that the fungi that we commonly call molds are incapable of penetrating a plant's cell walls. As a consequence, molds will only consume those parts of the wood where the cell walls have been sheared off by a saw cut or by other damage. Because of this, molds will not cause much damage to solid wood but can do lots of damage to engineered wood where the wood cells have been cut, pounded, squished and otherwise molested to make them more palatable to molds.

This assertion seems plausible, though I suspect that there might be exceptions.

In contrast, I was recently treated to a presentation by a local mold "inspector" who said that mold fungi consume the wood that they grow on and, if they're not removed, they can cause structural failure. This statement conflicts with my experience. In my opinion, if a moldy piece of wood has failed, it's because it's also infected with rot fungi.

What does current science tell us about molds' ability to consume wood?

- Jim Katen, Oregon

I didn't have time to read it, but there ought to be some low-hanging fruit here: http://usasearch.gov/search?v%3aproject ... tion=list&

WJ

[pfallah]

Hi Jim:

the common molds are generally do not compromise the integrity of the wood like the more specialized fungi, wood rotters do. Molds in general do not simply have the mechanism of consuming complex material like Cellulose, hemicellulose, and lignin (all of which are component of wood). The wood decay fungi however are capable of consuming these complex molecules.

Now some mold fungi like Chaetomium can rot the wood and are included on the soft-rot category all by themselves. The are no way close to the level of destruction that white rot or brown rot fungi are capable to cause.

The typical molds are not generally capable of penetrating the cell wall because they are generally Saprophyte (live on dead organic material) and not plant pathogens that require live tissues. I hope this helps.

best

[Jim Katen]

Thanks Walter & Payam.

- Jim Katen, Oregon

[randynavarro]

If one sees "mold" on some wood, it must be identified accurately to know whether it will consume that wood or not, correct?

I personally am not able to identify the different species of mold fungi, therefore I can't make the statement that the mold I saw will destroy the wood. Also correct?

[pfallah]

Hi Randy:

For the most part yes, identifying the fungus would provide more info. But the basidiomycetes fungi (your mushrooms and nasty wood rots) have a unique pattern of growth that one could recognize almost immediately. They grow fan like and usually are lobed toward the edges. Mold colonies generally have very pronounced surface that is cottony or fluffy either because of heavy sporulation or just the mass of mycelium on the surface.

More importantly depending on how large of a surface the colonization is, in case of wood rotter (mainly basidiomycetes) you can stick a crew driver or knife to see if the wood is soft. If soft most likely what you saw on the surface is a wood rot. Again generally this is the case.

"I personally am not able to identify the different species of mold fungi, therefore I can't make the statement that the mold I saw will destroy the wood. Also correct?"

if macroscopic identification at the higher level (described above between basidiomycetes and general mold) not possible then yes, you are correct.

you can refer to this website of Univ of Minn.: http://rotban.typepad.com/files/univers ... od-rot.pdf

or better yet check out the book by Zabel and Morrell. Wood Microbiology. it is a fantastic book. You can also contact Dr. Quarles at cooperative Extension in Univ of California (UCCE),

hope this helps.

best

[Jim Katen]

If one sees "mold" on some wood, it must be identified accurately to know whether it will consume that wood or not, correct?

I personally am not able to identify the different species of mold fungi, therefore I can't make the statement that the mold I saw will destroy the wood. Also correct?

In my experience you can't see decay fungi till they'e already done their damage. If I see fungus growing on wood, and I scrape the surface to see bright wood underneath, it isn't a wood rot fungus.

Or am I mistaken?

- Jim Katen, Oregon

[pfallah]

Well, i dont know about scratching the surface and exposing the coloration. There are several tests. There is Pick or Splinter Test done on wood surfaces to test for decay. Per Zabel and Morrell (1992), you can drive a screwdriver or awl in the wood at acute angle and bent back to snap a small piece of wood from surface. Brash breaks tells you low strength and possible presence of decay. If splintery breaks then you have sound wood. it is a good indicator of early decay.

[Jim Katen]

Well, i dont know about scratching the surface and exposing the coloration. There are several tests. There is Pick or Splinter Test done on wood surfaces to test for decay. Per Zabel and Morrell (1992), you can drive a screwdriver or awl in the wood at acute angle and bent back to snap a small piece of wood from surface. Brash breaks tells you low strength and possible presence of decay. If splintery breaks then you have sound wood. it is a good indicator of early decay.

According to Morrell, it's the *only* test for detecting decay before it becomes visible. I believe he also said that a brash break indicates that the wood has already lost 90% of its strength. I've never heard of any field test to identify the presence of rot fungi in the earliest stages.

It seems to me that when I can *see* a fungus growing on a piece of wood, if it's a rot fungus, then the wood will already be toast. If the wood isn't already toast, it's probably not a rot fungus.

- Jim Katen, Oregon

[Bain]

Well, i dont know about scratching the surface and exposing the coloration. There are several tests. There is Pick or Splinter Test done on wood surfaces to test for decay. Per Zabel and Morrell (1992), you can drive a screwdriver or awl in the wood at acute angle and bent back to snap a small piece of wood from surface. Brash breaks tells you low strength and possible presence of decay. If splintery breaks then you have sound wood. it is a good indicator of early decay.

According to Morrell, it's the *only* test for detecting decay before it becomes visible. I believe he also said that a brash break indicates that the wood has already lost 90% of its strength. I've never heard of any field test to identify the presence of rot fungi in the earliest stages.

It seems to me that when I can *see* a fungus growing on a piece of wood, if it's a rot fungus, then the wood will already be toast. If the wood isn't already toast, it's probably not a rot fungus.

- Jim Katen, Oregon

What's a "brash break?" I Googled with no luck.

[pfallah]

here is a site that can help with picture, copy paste:

http://books.google.com/books?id=0TMWGF ... #PPA127,M1

best

[Bain]

here is a site that can help with picture, copy paste:

http://books.google.com/books?id=0TMWGF ... #PPA127,M1

best

That was great. Thank you.

[Chris Bernhardt]

So can we then conclude that it's the condition of the surface of hygroscopic materials even after the hygric buffering capacity has been reached that determines also if mold will take root or not?

Assuming that we had such a thing as an atomic saw that could make clean cuts of the constituents of wood.

Chris, Oregon