Annual sudden oak death survey underway to test for spread, activity of tree-killing organism

About 30 feet beyond the last infected tree, across the trail that winds through LandPaths’ Riddell Preserve, Steve Ineich peered through the branches of a California bay laurel and called to the team, “Got another one!”

He pulled off a few leaves that bore the telltale signs — brown tip, inky black line, yellow margin, tiny black spots or larger lesions. He put the leaves in an envelope marked with GPS location and other pertinent data to be turned in for verification at a UC Berkeley lab, which in the coming weeks will receive hundreds of such samples to test for sudden oak death, or SOD.

Ineich, a Healdsburg resident, and other volunteers and LandPaths staff are contributors to California’s SOD Blitz Project, an annual survey that helps measure the extent of a disease that has gradually marched along the coast of California since it was discovered in Marin County in 1995.

The idea is to catch it early, in the vector host, before it can spread to a susceptible tree, said Matteo Garbelotto, adjunct professor and Cooperative Extension Specialist at Cal Berkeley, who launched the SOD Blitz in 2008.

The grassroots effort also helps homeowners associations, open space agencies, native tribes, land trusts and community organizations like LandPaths, a nonprofit conservation and land stewardship group, to decide if there are infected trees they should cull or treat.

Several bay trees tagged Friday at LandPaths 400-acre Riddell Preserve, for instance, were rooted mere inches from black oaks and coast live oaks, both among the species susceptible to sudden oak death, so they probably need to come out, Stewardship Field Specialist Miles Sarvis-Wilburn said.

Walking on, he pointed to several small saplings. “Just in terms of stewardship, I’ll probably lop these two in the future,” Sarvis-Wilburn said.

LandPaths solicited volunteers for two survey days this week: Thursday at its Bohemia Preserve near Occidental, and Friday at Riddell Preserve, in the hills west of Healdsburg.

A similar, event was scheduled Saturday at Fairfield Osborn Preserve in Penngrove and Monday at Galbreath Preserve in Yorkville. Both are hosted by the Sonoma State University Center for Environmental Inquiry.

But the citizen survey, now in its 18th year, also is an opportunity for individual property and homeowners to inspect trees on their own land for signs of an organism that could take out their beloved oaks, and then go on to infect a neighbor’s trees.

Those folks actually account for the bulk of participants in the state blitz and, in Sonoma County, have the rest of May to take part, as long as they register in time to have their packets mailed by May 24, said Kerry Wininger, Sudden Oak Death program coordinator for the University of California Cooperative Extension in Sonoma County. Wininger helps facilitate the blitz in Sonoma and Mendocino counties.

A brief training video also is required.

About 100 individuals were involved in the Sonoma County blitz last year, Wininger said. “We’re hoping to get another 80 to 100 people this year,” she said.

The findings will be analyzed this summer and released next fall, revealing infection rates in different coastal areas surveys.

Now confirmed in 16 California counties from Monterey County to southwest Oregon, the pathogen responsible for sudden oak death — an algae-like organism called Phytophthora ramorum — is estimated to have killed well over 50 million oak and tanoak trees.

It is spread largely in water droplets containing spores that are blown or that fall from bay laurel trees, which serve as hosts but don’t die from the disease. One hundred or more other plants also serve as vectors without becoming symptomatic, though the common California bay laurels are the most common offenders.

It also can be spread in mud on boots and vehicle tires, for example.

Tens of millions more trees are infected, though they sometimes take a few years to succumb, despite the hasty demise suggested by the disease’s name.

What’s sudden about it is how rapidly an oak’s leaves turn brown one to three years after infection, often with no other sign of disease. Oozing, bleeding cankers with a sticky dark or reddish hue sometimes appear on the lower trunks of dying oak trees — outward signs of the inner damage that destroys a tree’s conductive tissue and cuts off the flow of water. Shreve’s oak, canyon live oak and tanoaks also are vulnerable to the disease. Tanoak trees also serve as hosts and can become symptomatic and die, as well.

The disease is widespread in Sonoma County, and most likely is worst in the west, where it’s well established in tanoak trees and bay laurel found in mixed redwood forests, Garbelotto said.

It tends to be more cyclical in the mixed oak woodlands in east Sonoma County, near Lake and Napa counties, where fluctuations in the disease are more common than elsewhere, he said.

Between Santa Rosa and Petaluma and the Sonoma Valley and Sonoma, and especially on Sonoma Mountain, which offers a particularly “favorable” environment for the pathogen, Sudden Oak Death is a reliable presence. In much of that area, it is spread less readily between oaks than it is between tanoaks in west county, Garbelotto said.

But weather plays a key role, and during recent, extreme drought, the pathogen retreated in some areas, including some places where, by last year, it could not be detected after 15 years of affirmative samples, Garbelotto said.

The late winter rain this year is expected to change that trend. The Phytophthora ramorum can go from an essentially dormant state to infectious in as little as 36 hours, with rain, Garbelotto said.

But temperature plays a role, and cool, damp weather may be less likely to drive mass infection than warm rain, he said.

Shifts in the pathogen’s reproductivity and ability to spread also are not linear, and it’s likely this is the first in a two-year period during which the disease will rise toward a threshold of greater infection.

Overall, however, “we expect the disease to become prevalent again, and we do know from the past, it could do that rapidly,” Garbelotto said.

You can reach Staff Writer Mary Callahan (she/her) at 707-521-5249 or mary.callahan@pressdemocrat.com. On Twitter @MaryCallahanB.