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Dry conditions keep sudden oak death in check, yet significant outbreaks continue

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Google map shows results of the SOD blitzes available online at sodblitz.organd SODMAP.org. Green icons identify trees sampled that tested negative for SOD. Red icons were SOD-infected trees.
 
 
Sudden oak death, which has killed millions of trees in California over the past 20 years, is spreading more slowly, according to California's most recent citizen-science sudden oak death survey. The 2018 SOD Blitz results indicate Phytophthora ramorum (the pathogen known to cause SOD) infection is currently less prevalent in many wildland urban interface areas, though significant outbreaks are still occurring in some locations.

Overall, 3.5 percent of the trees (based on those areas sampled during the blitzes) were found to be P. ramorum positive, a threefold drop from 2017. Yet, in San Mateo, Santa Clara and Santa Cruz counties, infection levels were estimated to be as high as 19 percent, followed by 12.7 percent in the East Bay.

 
"SOD blitzes detected the highest levelsoffoliar infections by OD in 2017,” said SOD BlitzfounderMatteoGarbelotto, UC Berkeley forest pathology and mycology Cooperative Extension specialist and adjunct professor. “As predicted, those high levelsoffoliar infections were responsible for a high increase of infection of oaksandtanoaks by SOD.

"Oaks and tanoaks were infected last year and will be showing symptoms such as bleeding in the stem and canopy drying this year and in the next two years to follow. Hence, despite a reduction of SOD infection on leaves of California bay laurels and leaves of tanoaks in 2018, we can expect a sharp increase in oak and tanoak mortality in 2018, 2019 and 2020."

Notable outbreaks were detected in Alameda (El Cerrito and Oakland urban parks, San Leandro, Orinda, Moraga), Marin (Novato, Day Island, Woodacre, Sleepy Hollow, McNears Beach, China Camp State Park, north San Rafael, Tiburon Peninsula, east and west peak of Mt. Tamalpais, Marin City), Mendocino (south of Yorkville), Monterey (Carmel Valley Village, Salmon Creek Trail in southern Big Sur), Napa (east Napa city), San Mateo (Burlingame Hills, west of Emerald Hills and south of Edgewood Rd, Woodside ), Santa Clara (Los Altos Hills, Saratoga, Los Gatos, along Santa Cruz Co border), Santa Cruz (along the Santa Clara Co border, Boulder Creek), and Sonoma (near Cloverdale, east and west of Healdsburg, west of Windsor, east of Santa Rosa, west of Petaluma) counties.

Several popular destinations where P. ramorum was found positive during the 2017 Blitz were negative for the pathogen in 2018, including Golden Gate Park and the Presidio of San Francisco, the UC Berkeley campus, and Mount Diablo State Park. Samples from San Luis Obispo and Siskiyou counties were also pathogen-free as were those from the southern portion of Alameda County.

"We encourage everyone in affected counties to look at the Blitz results online and to attend one of the fall workshops to learn how to protect their oaks from SOD,” Matteo Garbelotto.

“It is encouraging that SOD has yet to be found in the forests of California's northern-most counties, San Luis Obispo County and southern Alameda County,” said Garbelotto.

“It is also encouraging to see that despite its continued presence in the state for more than 20 years, SOD infection rates drop during drier years,” he said. “However, in 2018, we identified a number of communities across several counties where significant outbreaks were detected for the first time, and the Salmon Creek find in Monterey County is the southernmost positive WUI (wildland-urban interface) tree detection ever. Until the 2018 Blitz, only stream water had been found positive in the Salmon Creek area. We encourage everyone in affected counties to look at the Blitz results online and to attend one of the fall workshops to learn how to protect their oaks from SOD.”

Citizen-science SOD Blitz workshops

SOD Blitz Workshops are being held this fall in Santa Rosa (Oct. 10), Portola Valley (Oct. 16) and Berkeley (Oct. 17). The trainings will discuss Blitz results and recommendations for protecting oaks in the WUI. Workshops are intended for the general public, tree care professionals and land managers (see www.sodblitz.org for details). Two International Society of Arboriculture continuing education units will be offered at each training. Data collected from the Blitz (both positive and negative samples) have been uploaded to the SOD Blitz map (www.sodblitz.org ) as well as to SODmap (www.SODmap.org) and to the free SODmap mobile app, which can serve as an informative management tool for people in impacted communities.

SOD Blitz volunteers collect leaf samples and record the location using the SODmap mobile app.

Twenty-five SOD Blitz surveys were held in 2018 in the WUI of 14 coastal California counties from the Oregon border to San Luis Obispo County and included three tribal land surveys. The 304 volunteers surveyed approximately 13,500 trees and submitted leaf samples from over 2,000 symptomatic trees to the Garbelotto lab for pathogen testing.

SOD Blitzes are a citizen science program, which train participants each spring to identify symptomatic tanoak and California bay laurel trees in the WUI and to properly collect samples in the interest of generating an informative map of P. ramorum disease symptoms over time. Samples are tested for the presence of the pathogen at UC Berkeley and results are posted electronically each fall. Now in its eleventh year, the SOD Blitz program is one of the first in the world to join researchers and volunteers in a survey for a tree disease.

SOD Blitz surveys were made possible thanks to funding from the US Forest Service State and Private Forestry, Midpeninsula Regional Open Space District, and the PG&E Foundation. The Blitzes were organized by the UC Berkeley Garbelotto lab in collaboration with the National Park Service, Presidio Trust, San Francisco Public Utilities Commission, Midpeninsula Regional Open Space District, Save Mount Diablo, Land Trust of Santa Cruz County, East Bay Regional Park District, Santa Lucia Conservancy, Sonoma State University, UC Santa Cruz Arboretum, Los Padres National Forest, City and County of San Francisco Department of Recreation and Parks, UC Berkeley Botanical Garden, and California Native Plant Society.

Video of Dr. Matteo Garbelloto describing the three steps to managing sudden oak death.

For information on the status of P. ramorum/SOD tree mortality in California wildlands, see the US Forest Service 2018 Aerial Detection Survey results at https://www.fs.usda.gov/detail/r5/forest-grasslandhealth/?cid=fseprd592767.

For more information on the SOD Blitzes, visit www.sodblitz.org or contact Katie Harrell at (510) 847-5482 or kmharrell@ucdavis.edu. For more information on Sudden Oak Death and P. ramorum, visit the California Oak Mortality Task Force website at www.suddenoakdeath.org or contact Harrell.

 
Posted on Tuesday, October 9, 2018 at 4:30 PM
  • Author: Katie Harrell

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Posted on Monday, February 13, 2017 at 2:51 PM
  • Author: Pamela Kan-Rice

Citizen science helps predict sudden oak death

Reprinted from the UC Berkeley News Center.

Efforts to predict the emergence and spread of sudden oak death, an infectious tree-killing disease, have gotten a big boost from the work of grassroots volunteers.

Two volunteers collect samples in the East Bay during the 2014 SOD Blitz. (Photo by Douglas Schmidt, UC Berkeley)
Two volunteers collect samples in the East Bay during the 2014 SOD Blitz. (Photo by Douglas Schmidt, UC Berkeley)

A joint study reveals the power of citizen science in SOD Blitz, a survey project in which volunteers are trained to identify symptoms of sudden oak death. Led by Matteo Garbelotto at UC Berkeley and Ross Meentemeyer at North Carolina State University, the study was published today (Friday, May 1) in the journal Frontiers in Ecology and the Environment.

Sudden oak death is a fungus-like disease that has felled hundreds of thousands of trees in California. Crowdsourcing the survey and sampling work allowed researchers to gather information that would otherwise be too impractical and cost-prohibitive to obtain. Researchers then used the data to create a model that predicts the presence of the sudden oak death pathogen, Phytophthora ramorum, based upon such variables as rainfall and density of host trees.

Study authors compared the model based upon crowdsourced data gathered from the 2008-2013 blitzes with models using “pre-Blitz” research observations collected from 2000 to 2007. They found the SOD Blitz model to be more powerful, correctly predicting the presence of the pathogen 74 percent of the time, compared with models based on other sources of data.

Shown is a laminated card given to SOD Blitz volunteers as part of a package with collection materials. The card helps citizen scientists correctly identify signs of SOD infection.
Shown is information from a laminated card given to SOD Blitz participants as part of a package when they volunteer. The card helps citizen scientists correctly identify signs of SOD infection. (Courtesy of Douglas Schmidt, UC Berkeley)

“This paper shows that volunteers are as proficient as professionals in collecting data after they get some initial training,” said study principal investigator Garbelotto, an adjunct professor and cooperative extension specialist at UC Berkeley's Department of Environmental Science, Policy and Management. “The data we got from SOD Blitz resulted in the formulation of the best predictive model yet about the spread of sudden oak death in California. Additionally, we were able to identify new infestations and identify trees that needed to be removed. In one case, in Atherton, tree removal resulted in the only successful eradication of the pathogen in North America.”

The SOD Blitz model also revealed novel findings about the spread of the disease, finding that average population density and average maximum temperature were negatively correlated with the presence of the sudden oak death pathogen.

“The population density finding is important because of the debate about the role of humans in spreading sudden oak death disease,” said Garbelotto. “From this work we can say that humans are not currently spreading the disease, and that the pathogen is doing well spreading on its own.”

Beginning the Blitz

Jean Morrell, a retired biologist living on the Santa Lucia Preserve in Monterey County, learned about sudden oak death in 2007 through an on-site presentation and subsequent hike with Garbelotto that was organized for the homeowners on the preserve. The event provided the seeds for the idea of the SOD Blitz as a way to get more people – particularly other homeowners on the preserve – engaged. For Morrell, the idea kicked off a round of phone calls and personal outreach to her neighbors.

UC Berkeley's Matteo Garbelotto meets with SOD Blitz volunteers in Los Altos Hills. Citizen scientists are given hands-on training during these mandatory meetings to ensure that sampling is done properly. (Photo by Douglas Schmidt, UC Berkeley)
UC Berkeley's Matteo Garbelotto meets with SOD Blitz volunteers in Los Altos Hills. Citizen scientists are given hands-on training during these mandatory meetings to ensure that sampling is done properly. (Photo by Douglas Schmidt, UC Berkeley)

Garbelotto launched SOD Blitz the next year, in 2008, and it has since grown into one of the largest citizen science projects in the country, incorporating 21 coastal communities in California. Each spring researchers reach out to participants through news stories, radio announcements, community groups and other recruitment methods.

Participants go through mandatory, on-the-ground training by professionals to learn how to detect and sample infected trees. Training workshops last about an hour, and then volunteers are provided with symptom detection guides, a mobile mapping tool and packets for storing leaf samples.

“When it comes to predictive models, the more data the better,” said study lead author Meentemeyer, a professor of forestry and environmental resources and director of the Center for Geospatial Analytics at North Carolina State University. “This is especially true in less-studied urban ecosystems and people's backyards, where research scientists typically have little to no data. But the data need to be good, otherwise researchers are left dealing with a lot of noise. Motivated people, given a minimal amount of training, are clearly able to provide information that researchers need.”

‘People want to protect their trees'

In any one year, the return rate of participants ranges from 15 percent to as high as 40 percent, Garbelotto noted.

“From that first Blitz, we developed a core group of workers that have continued their interest and have followed up year to year,” said Morrell. “Sudden oak death is in all of our backyards, and it will have an effect on our neighborhoods. This is why we can engage people in the program. It not only allows participants to monitor their own space, but also, if they so desire, they can tromp out into the woods and do work in more remote areas. One only has to give up some ‘sweat equity' to participate, and the results are available to everyone at no cost. It's a win- win.”

Many participants are attracted to SOD Blitz by a shared love of the environment.

“I am an environmentalist, and my passion is trees. I believe they are the lungs of the Earth,” said Debbie Mendelson, who recruits SOD Blitz volunteers as a member of the Woodside Sustainability and Conservation Committee. “I think first and foremost, people want to protect their trees. Then there are folks who want to do something for the good of their community.”

Mendelson noted that SOD Blitz has also provided an opportunity to engage students in science. She has given presentations at local high schools about sudden oak death and citizen science. “I think it is a fantastic opportunity for students who have an interest in science to hear a scientist speak in an understandable and warm manner,” she said.

This year's SOD Blitz recruitment has already begun. Community meetings will be held at various locations through early June for those interested in learning more.

Once verified, data from SOD Blitz is uploaded and freely available online.

The National Science Foundation, U.S. Forest Service, Gordon and Betty Moore Foundation and PG&E Foundation helped support this work.

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Posted on Tuesday, May 12, 2015 at 4:52 PM
  • Author: Sarah Yang
 
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