Home > Newsletter Archives > Vol: 03/21/2018
  • The Issue of Stain and Mold in Relation to ISPM 15

  • Stain

    Stain in wood can develop in several ways.  These include:

    • Minerals absorbed by the tree during its growth.
    • Chemical reactions between the tree tannins and certain metals.
    • Sun exposure.
    • Fungal activity.

     

     

     

     

     

     

    Concern surrounds mainly the stain related to fungal activity.  This sort of stain can be a common occurence during warmer weather caused by certain dark-colored microscopic fungi creating a discoloration that develops in the sapwood of the tree. Conditions that promote fungal activity are:

    1. Temperatures at 50 - 120 F.
    2. Wood moisture content > 40% or relative humidity > 90%.
    3. Availability of oxygen. 
    4. Nutrients like the sugar in the sap.

    The color of stain ranges from black or grey to red or orange.  In pine, blue stain does not affect the strength or performance of structural lumber and therefore the grade is not affected either. 

    In any of these situations, stain poses no threat to forest stands and is therefore not covered under ISPM 15. 

    One caveat to this is that Australia regards blue stain fungi as associated with beetles covered under ISPM 15.  Care should be taken when using WPM to ship there.

  • Mold

    Mold is a type of fungi that lives off the sugars in the wood.  It develops on the wood surface mainly as a result of airborne spores after the wood has been cut. 

     

     

     

     

     

    For mold to develop, the conditions must be right and include:

    • Warmer temperatures (50 to 90 F)
    • Oxygen,
    • A food source (wood fiber).
    • Moisture. 

    Mold will manifest on the wood surface as a fuzzy or powdery substance with colors ranging from light pink to black.  While this surface material is generally easy to brush off, residual stain may remain in the wood fiber.  The conditions that allow mold to grow can also lead to decay if not addressed.

    Regardless of the circumstances, mold itself does not pose a risk to forest stands and is not covered under ISPM 15. 

  • Ways to Mitigate Mold

     

     

     

     

     

     

    In order to mitigate mold development in lumber, mills may apply an anti-fungal chemical to the lumber in order to poison the thin outer layer to eliminate the risk of any new fungal stain or mold.  This is only a temporary fix as most chemicals lose their effectiveness after about 3 weeks. 

    The best way to control mold is to eliminate one of the four conditions that allow it to develop.  This is typically addressed on the moisture side.  Kiln drying wood (dried to a moisture content of 19% or less) and keeping it dry is the most effective way to prevent mold growth.  The kiln drying process is typically done at a rate that initially prevents mold development.  For the ISPM 15 standard, lumber must also be heat treated and lumber that is both kiln dried and heat treated will be designated on the grade mark as "KDHT".  Once a facility receives KDHT lumber it should be properly stored to avoid being re-exposed to moisture which could allow mold to grow.  Pallets built from KDHT lumber require the same care as the lumber to avoid mold issues from developing.  

    While mold and stain are not restricted by ISPM 15, many customers frown on these being on their WPM.  However, using the proper preventive measures at a facility can greatly reduce the development of these two potentially problematic issues.