Sudden Oak Death

by David Rust

What is Sudden Oak Death?

The plant pathogen Phytophthora ramorum is the cause of both Sudden Oak Death, a forest disease that has resulted in widespread dieback of several tree species in California and Oregon forests, and Ramorum blight, which affects the leaves and twigs of numerous other plants in forests and nurseries. This disease is of major concern to foresters and the California ornamental nursery industry. It is also a major concern to wild mushroom collectors, as some of the trees with mycorrhizal associations with choice edible mushrooms are suffering the highest mortality from the disease.

Current status

Record-breaking spring rains in 2006 may have aided in the spread of Sudden Oak Death in Sonoma, Marin, and Mendocino counties. Aerial surveys just completed by the USDA Forest Service and Cal Poly San Luis Obispo found many potential diseased forest lands. Follow-up ground surveys to gather symptomatic vegetation samples for laboratory diagnosis are still under way. Results so far from the California Department of Food and Agriculture and the Rizzo, UC Davis lab show two new P. ramorum confirmations in southern Mendocino County in the Indian Creek and Navarro River watersheds between Ukiah and Booneville. P. ramorum has not been found in Salt Point State Park, but surrounding woodlands are heavily infected and it is just a matter of time before Salt Point succumbs.

What you can do

Learn the signs of Sudden Oak Death and ways to prevent its spread. If possible, avoid areas that are showing symptoms of diseased trees. Spores of P. ramorum can adhere to your clothing. The pathogen can also adhere to leaf litter and mud on your shoes. If you visit a forest with symptoms of P. ramorum, knock off any loose soil or mud while still in the area, and wash off your clothes and boots when you get home. Better yet, keep two sets of clothes for trips to infected and uninfected areas. Avoid transporting water from known infected areas.

More info

About the author

David Rust is a SOMA member and co-founder of the new Bay Area Mycological Society. He's written several articles on Sudden Oak Death for Mushroom, the Journal of Wild Mushrooming, and has been a member of the California Oak Mortality Task Force since it was created in August 2001. David helped organize the first-ever All California Club Foray and the MycoBlitz Forays at Pt. Reyes National Seashore.