March 9, 2020 – In California, sudden oak death disease has killed more than 50 million of the state’s iconic oaks and tanoak trees between Humboldt County and Monterey County, threatening survival of several tree species. In 2019 alone, 1 million tanoaks succumbed to sudden oak death (SOD), according to 2019 tree mortality data released by the U.S. Forest Service.

“Two new dangerous SOD strains are at the doors of our forests,” said Matteo Garbelotto, UC Cooperative Extension forest pathology specialist, in the Department of Environmental Science, Policy and Management at UC Berkeley. To assess the movement of SOD, he has mobilized citizen scientists for what he calls “SOD blitzes.” The first in a series of SOD blitzes of 2020 will be April 11 in Napa.

“We had some great results last year and participation continued to be good after 13 years of SOD blitzes,” Garbelotto said.

In Sonoma County, the 2019 SOD infection rate doubled that of 2018, and in Napa County, SOD detection was four times higher than the previous year. In the East Bay, between Richmond and San Leandro, SOD infection spiked – from 1 to 12 percent. The SOD infection rate tripled — from 6% to 18% on the western slopes of the Santa Cruz Mountains in San Mateo County.

As the disease expands its path of forest destruction, the UC Cooperative Extension scientist says more volunteers are needed to sample trees.

“The disease is moving to new counties outside of the current area of infestation,” Garbelotto said. “Even in our Bay Area neighborhoods, SOD of 2019 is not the same SOD of 10 years ago: different distribution, new local outbreaks, and new hosts are emerging, as the disease becomes more and more established in its new home.”

Garbelotto sees the SOD blitzes as the only hope for early detection of the new SOD strains.

“If these new strains arrived and spread in our forests, they could deliver a fatal blow to our forests,” he said. “By collecting symptomatic plant material in their neighborhoods, volunteers will make the most significant contribution possible to intercept these strains.” 

Volunteers are taught to identify SOD symptoms and to carefully collect symptomatic leaves from California bay laurels and tanoaks. Participants in the SOD blitzes will be asked to quantify their efforts to stop SOD to show public interest in saving oaks and tanoaks when applying for funds to defeat the tree-killing disease.

Garbelotto is encouraging tree care specialists to participate in the SOD blitzes.

“We have enhanced the benefits for tree care professionals who participate in the blitzes,” Garbelotto said. “Besides offering free bay laurel and tanoak tests for their clients, we now offer them free enrollment in UC Berkeley Forest Pathology Laboratory’s OakSTeP program, which allows tree care professionals to test oaks for SOD infection. It could be enormously beneficial to everybody.”

For more information about the SOD blitzes, visit or

Sudden Oak Death Blitzes 2020

Trainings will last one hour, samples have to be collected after the training, all collection materials will be provided, but bring a mobile phone or GPS device. Please install the free SODmap mobile app before the meeting.

Saturday, April 11: The Napa Blitz

10 a.m.-11a.m., UC Cooperative Extension classroom, 1710 Soscol, Napa

Contact: Bill Pramuk

Tuesday, April 14: The Santa Cruz Blitz

6:30 p.m.-8 p.m. UC Santa Cruz Arboretum

Contact: Brett Hall

Saturday, April 18: The Carmel Valley, Big Sur and City of MontereyBlitzes

10 a.m.-noon. Palo Corona Discovery Center (part of the Monterey Peninsula Regional Park District) 4860 Carmel Valley Rd, Carmel-By-The-Sea, CA 93923

Contacts: Kerri Frangioso

Justin Prouty

Santa Lucia Preserve (For local residents only)

Contact: Christy Wyckoff

Wednesday, April 22: The Karuk Nation Blitz

5 p.m.-6 p.m. Orleans at the Karuk Tribe’s Council Chambers

Contact: Heather Rickard

April 25: The Saratoga & Skyline Blitzes

10 a.m. West Valley College, Auditorium of the Science and Math Department

Contact: Ann Northrup

CNPS: Toni

MidPen Open Space Contact: Coty Sifuentes

City of Saratoga: Kate Bear

1 p.m.-2 p.m., SOUTH SKYLINE, Saratoga Summit Forestry and Fire Protection (CalFire) CDF fire station. 12900 Skyline Blvd, Los Gatos, CA.

Contact: Jane Manning

MidPen Open Space Contact: Coty Sifuentes

Saturday, May 2: The East Bay Blitzes

10 a.m.-11:30 a.m. Gallery Room, Orinda Library, 26 Orinda Way, Orinda, Ca. 94563

Contact: Bill Hudson

1 p.m.-2 p.m., Morgan Lounge, Morgan Hall, UC Berkeley Campus

Contacts: Doug Schmidt

Anna Marie Schmidt

Tuesday, May 5: The San Francisco Blitz

9 a.m.-10 a.m., County Fair Building, Recreation Room, Golden Gate Park San Francisco

Contacts: David Iribarne

Christa Conforti

May 2-7: The Sonoma and Kashia Blitzes

Saturday, May 2, 9 a.m.-1 p.m., Sonoma State University’s Galbreath Preserve

Meet at the Yorkville Post Office, 25400 CA-128, Yorkville; Participants will attend a 1-hour training, then have the option to attend a docent-led visit to the preserve to collect samples on site. More information:

Sunday, May 3, 9 a.m.-noon Sonoma State University’s Fairfield Osborn Preserve, Lichau Rd., Penngrove, 94951

Samples will be collected during the event on site.

*This is a bilingual event (English and Spanish) / Este es un evento bilingue (Inglés y Español)

More information:

3) Petaluma

Thursday, April 30, evening time TBD, specific location TBD

4) Cloverdale

Date/time and specific location TBD

5) Kashia Pomo tribal lands (private group)

 Date/time and specific location TBD

May 2-9: The North Peninsula Blitz

Training online at

Contact: Steve Epstein

Saturday, May 9: The Marin Blitz

10 a.m.-11 a.m., San Rafael, Dominican College, Joseph R. Fink Science Center, Room 103.

Contacts: Wolfgang Schweigkofler

CNPS Marin Kristin Jacob

May 15 and 16: The San Luis Obispo Blitzes

Friday, May 15, 6:30 p.m.-7:30 p.m., at the SLO County Atascadero Library, Martin Polin Community Room, 6555 Capistrano Ave, Atascadero, CA.

Saturday, May 16, 8:30 a.m.-9:30 a.m., at the SLO County Department of Agriculture, UCCE Auditorium, 2156 Sierra Way, San Luis Obispo, CA.

Contacts: Kim Corella

Lauren Brown

May 19-22: The North Coast Blitzes, Humboldt & Del Norte

Date and location TBA

Contacts: Chris Lee

Yana Valachovic

Saturday, May 30: The Peninsula SOD Blitz

Woodside/Portola Valley/Los Altos Hills/Atherton/Redwood City

10 a.m.-11 a.m., Portola Valley Town Center, 765 Portola Rd.

Contacts: Debbie Mendelson

LAH: Sue Welch

MidPen Open Space: Coty Sifuentes

Emerald Hills: Rochelle Kopp

Saturday, June 6: The Mendocino County Blitz

10 a.m.-11:30 a.m., Historical Farmhouse at the Mendocino Coast Botanical Gardens, 18220 North Highway 1, Fort Bragg, CA 95437

Contacts: Mario Abreu

Michael Jones

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