What is sudden oak death and can it be treated?

Sudden oak death (SOD) is a disease caused by the pathogen Phytophthora ramorum . It has killed millions of oaks and tanoaks in coastal California and is well established in San Mateo County - UC Berkeley's 2025 survey rates parts of the Peninsula a high-risk zone. The pathogen typically reaches oaks from infected California bay laurel growing nearby; bay leaves host it, rain splashes it onto oak trunks. What owners of oaks should know: Symptoms: dark bleeding cankers on the trunk, rapid browning of the crown, and in late stages beetle boring dust No cure exists for an infected oak - late-stage trees should be removed before they become brittle hazards Prevention works: phosphonate treatment protects healthy high-value oaks, and removing bay laurel within about 15 feet of an oak's trunk is the single most effective step Timing matters: avoid wounding oaks in the wet season when spores travel If an oak shows trunk bleeding or fast crown decline, have it assessed promptly - our arborist confirms whether it is SOD, root disease, or drought stress, and what is actually worth doing.

Sudden oak death (SOD) is a disease caused by the pathogen Phytophthora ramorum. It has killed millions of oaks and tanoaks in coastal California and is well established in San Mateo County – UC Berkeley’s 2025 survey rates parts of the Peninsula a high-risk zone. The pathogen typically reaches oaks from infected California bay laurel growing nearby; bay leaves host it, rain splashes it onto oak trunks.

What owners of oaks should know:

Symptoms: dark bleeding cankers on the trunk, rapid browning of the crown, and in late stages beetle boring dust
No cure exists for an infected oak – late-stage trees should be removed before they become brittle hazards
Prevention works: phosphonate treatment protects healthy high-value oaks, and removing bay laurel within about 15 feet of an oak’s trunk is the single most effective step
Timing matters: avoid wounding oaks in the wet season when spores travel

If an oak shows trunk bleeding or fast crown decline, have it assessed promptly – our arborist confirms whether it is SOD, root disease, or drought stress, and what is actually worth doing.