Can wood chips spread disease?

We often get asked if we sell or deliver wood chips. The answer comes in two parts. First we avoid chipping if possible because it is a more dangerous and noisy processed than loading a brush trailer and delivering it to the city’s composting facility. But secondly there are concerns that distributing wood chips we may be spreading disease from one property to another.
Can wood chips spread disease?
Uncomposted Wood chips have been known to carry pathogens such as Cytospora, Thyronectria, and Verticillium. Studies show that these pathogens are rarely spread to healthy trees (which in an urban environment unhealthy trees are quite common) by wood chip mulch but with even a slight possibility we prefer not to risk the spreading of plant pathogens that could harm a clients tree.
Is it safe to use wood chips as mulch?
The short answer is we only recommend using wood chips produced from your own property. This assures that you are not importing or contributing the spread of tree diseases.
What can we do to assure wood chips aren’t spreading disease?
- Most importantly keep your tree healthy! A healthy tree has stronger immunity and resists pathogens. A stressed or physically damaged tree is highly susceptible to disease.
- Use wood chips from your own property as mentioned above
- “Season” or dry your wood chips for a year or more to allow time for pathogens to die out. The drier the better.
- Hot compost the wood chips. The city landfill uses this process to compost green waste at the landfill.
- If you can get small diameter wood chips. Wood chips larger than 1 inch are much more likely to harbor disease than more finely chipped debris
- DO NOT mix wood chips directly with the soil, this puts the chips directly in contact with the roots increasing the chance of infection.
- Don’t over water your lawn/landscape. Overwatering encourages fungal growth and anaerobic soil which are fertile ground for plant pathogens to spread.
What is a good alternative to wood chips?
An easy material that can be obtained in large quantities for use as mulch is tree leaves! In their natural environment tress have thick layers of leaf litter beneath their canopy. Leaves can be used immediately after they fall or for a finer mulch that is less likely to blow away a leaf mulcher or lawn mower can be used to process the material into smaller pieces
Trees are alive and breathing but react much slower than we do. It can take years for a tree to die from stress or show symptoms of disease. It is important to take all the care we can in preserving our trees. Along with the other well know benefits healthy mature trees can increase the value of a house up to 15% percent. Knowing this it isn’t worth using wood chips from an unknown source if there is the possibility of damaging your irreplaceable tree.
Sources:
University of Washington on Wood chips:
https://s3.wp.wsu.edu/.../2015/03/wood-chip-pathogens.pdf
Wisconsin Horticulture on wood chips
https://hort.extension.wisc.edu/.../wood-mulch-and-tree.../
University of Washington trees and property values
https://www.naturewithin.info/Policy/Hedonics_Citations.pdf