Understanding and Managing Sudden Oak Death in California

1.4.3. Survival of SOD-Affected Trees

The extent to which cankers encircle the trunk can provide an indication of the how long the tree will survive (table 3-3). Coast live oaks with early symptoms (bleeding cankers only) are unlikely to die until they are colonized by beetles and/or A. thouarsianum.  Most coast live oaks with advanced trunk canker symptoms (beetle boring and/or A. thouarsianum colonization) that affect more than half of the trunk circumference will die within 1 to 3 years. However, coast live oaks with extensive SOD cankers colonized by secondary organisms have survived for 8 or even 11 years. Trees that live for many years despite extensive canker development tend to be relatively large diameter trees with no pre-existing heartwood decay in the trunk and relatively well-balanced canopy structure.

Most tanoaks that develop early P. ramorum canker symptoms die within three years. However, even tanoaks with extensive P. ramorum cankers may not develop obvious bleeding. Secondary invasion of the trunk by beetles colonization may be the first sign of disease. Consequently, the visible extent of trunk girdling by P. ramorum cankers is not always a reliable indicator of tanoak survival.

Both tanoaks and SOD-susceptible oaks commonly occur as multi-trunked trees. If the individual trunks arise from ground level, each trunk generally functions as a separate tree with respect to infection and disease progress. It may be possible to retain healthy trunks of multi-stemmed trees even if one or more stems have been infected or killed by SOD. However, remaining trunk(s) should be evaluated for structural stability. Decay associated with killed trunks may compromise the remaining trunks.