Understanding and Managing Sudden Oak Death in California

3.1.3. Firewood

Although cankers on intact oak and tanoak trees do not appear to produce sporangia under normal field conditions, chlamydospores can be formed within infected wood (Parke et al 2007). Under wet conditions, sporangia can be produced on the cut surfaces of wood from trees with P. ramorum cankers (Davidson and Shaw 2003, Davidson and others 2008). Therefore, movement of firewood cut from SOD-infected trees poses a risk of transporting P. ramorum to noninfested areas. State and federal regulations prohibit the movement of firewood collected from SOD hosts out of quarantined infested areas.

Burning wood from SOD-affected trees is an effective way to dispose of infected or potentially infected wood because burning destroys P. ramorum in the wood. There is no evidence that smoke or embers from infested wood can transport viable P. ramorum inoculum.

Wood cut from living infected trees or very recently SOD-killed trees have the greatest risk of serving as a source of P. ramorum spores. Wood from trees that have been dead for many years, even if killed by SOD, are unlikely to be a source of viable P. ramorum spores. For oaks, only the lower portion of the trunk of such trees are likely to have P. ramorum cankers; small-diameter wood from the upper part of the canopy is unlikely to be infected. In tanoak, wood of any size has the potential to be infected.

P. ramorum sporulation from cut firewood is only possible under wet conditions, so storing wood under dry conditions will eliminate the possibility that spores would form on firewood. Rapid drying of cut wood will also reduce the ability of the wood to support the reproduction of various wood boring beetles that could attack other trees in the area. Split and stack firewood in well-aerated piles in a dry, sunny location away from other host trees until it is thoroughly dry.

Wood can be also be solarized for several months to both speed wood drying and limit beetle reproduction. Cover woodpiles with a clear (not black) 6-10 mil thick UV-resistant polyethylene tarp that is sealed to the ground at the edges. The greenhouse effect created under the clear tarp heats the wood and speeds drying. Heating will be greatest if the stacks are relatively low (no more than 2-3 ft) and will be maximized in sunny locations under the long days from late spring through fall. Angle the sides of the tarp outward so that condensation that forms on the inside of the tarp will drain onto the soil.

If firewood is cut from either host or non-host trees within an infected area, P. ramorum may be moved along with infested California bay leaves, tanoak leaves and twigs, and soil that may be mixed in with the wood. Do not allow leaves and soil to be transported in or on firewood, equipment, or truck beds. Movement of infested soil can be minimized by cutting and loading firewood when soils are dry. Any California bay and tanoak leaves and twigs, soil, and other potentially contaminated material that are accidently moved to a new location should be collected and disposed of through burning or sealed in a bag for transport to a landfill.