The infection arrives with the rains, splashing down from a neighbor’s thick leaves. It takes hold one winter and persists silently for a year or two. Ambrosia beetles and bark beetles colonize the weakened tanoak, and the bark oozes and spots with dark-red liquid. Then, in a matter of weeks, the leaves brown and decay, and the tree dies.
Sudden oak death, a disease caused by the pathogen phyophthora ramorum, first appeared in an area…