Forest visitors spread oak pathogen

The mud caked on your hiking boots and bike tires from treks through the forest may help spread a pathogen that has ravaged oak trees in the West, new research shows.

Two Sonoma State University researchers found a higher incidence of symptoms of sudden oak death on land swamped with visitors. Rampant during rainy months, the incurable disease, caused by the fungus-like pathogen Phytophthora ramorum, sprouts bleeding cankers on bark and spells death for many oaks. About 30 trees and plants, including bay laurels, play host to the pathogen yet don’t die, but oaks such as the coast live oak and tanoak are killed by it. Thirteen Northern California counties were quarantined earlier this year once it spread to nursery plants such as camellias and rhododendrons, and at one point 10 states had banned the import of California plants.

The Sonoma State research, presented this month to the Ecological Society of America, showed that 40% to 100% of trails at Fairfield Osborn Reserve sampled carried the pathogen, while zero to 10% of off-trail samples were infected. Also, trees on well-traveled state and county parks in eastern Sonoma County had a higher rate of sudden oak death symptoms than those on private, rarely used land. This could mean that people transport the pathogen from place to place.

So what’s a trail user to do? For now, those who study sudden oak death use a diluted bleach solution and a dishwashing brush to scrub shoes after a hike.

--Ashley Powers