Posts Tagged: sudden oak death
Sudden Oak Death (SOD), a serious exotic tree disease, threatens the survival of tanoak and several oak species in California. Currently, SOD infects trees in 14 coastal California counties, from Monterey to Humboldt. The disease, which was estimated to have killed over 50 million oaks and tanoaks over two decades, has changed the coastal forests composition in Northern California and Southern Oregon.
Though SOD occurs in patches, the overall infection area continues to grow with each passing year. Researchers had previously discovered that Phytophthora ramorum, the pathogen that causes SOD, most often spreads on the leaves of infected California bay laurel and tanoak. Forest managers can use proactive methods for controlling the disease — including sanitation, chemical treatments, and the targeted removal of bay trees — but such tools are preemptive in nature, only useful before oaks and tanoaks are infected. Timely detection of the disease in these species is therefore critical to slowing the epidemic.
With this in mind, UC Berkeley joined with over 30 local organizers in 2019 to assemble 25 SOD Blitzes staffed by trained volunteers. More than 400 volunteers were taught to identify SOD symptoms and to carefully collect symptomatic leaves from California bay laurels and tanoaks. Armed with this training, the teams surveyed 16,227 trees across 16 California counties, collecting approximately 9,000 leaves from 1,732 symptomatic trees. Samples were sent to the UC Berkeley Forest Pathology and Mycology Laboratory for processing and analysis.
The benefits of SOD Blitzes are becoming increasingly clear. Importantly, they educate the community about Sudden Oak Death, getting locals involved in detecting the disease while creating detailed maps of infected areas. Analyses of these maps help forest managers figure out where proactive measures, such as chemical treatments or tree removal, most effectively stop an infestation. All results from the data collection are made publicly available on SODBlitz.org, SODMap.org, and on the SODmap mobile app available at the Apple Store and at Google Play. (Results can also be accessed directly on the UC Berkeley Forest Pathology and Mycology Laboratory website.)
Using the app allows anyone to estimate the risk of oak infection, specific to their current location. While standing next to a tree of interest, a person can tap the app's “RISK” button and determine whether an oak is in danger of contracting SOD. In addition, results meetings and treatment training workshops will be held for the public in various Bay Area locations during fall 2019.
Matteo Garbelotto, UC Cooperative Extension specialist and adjunct professor in the Department of Environmental Science, Policy, and Management, has led the SOD Blitzes for 12 years. The program enrolls approximately 500 volunteers yearly to canvas California woodlands for symptoms of SOD. Results of the surveys are made available nearly in real-time, immediately after completion of the lab analysis.
“We estimate that as many as two to three million people may have accessed the SOD Blitz results to determine whether trees on their property may be at risk,” Garbelotto said. “This is a huge success and shows the great societal value that citizen science has, and it highlights the importance of collaborating with volunteers on issues that are relevant to safeguard trees that are an important part of California's natural heritage.”
2019 SOD Blitz Results
Across the state, the number of trees infected with SOD, along with the estimated SOD infection rate, has almost doubled since 2018. In some areas, infection rates were as much as 10 times higher than the previous year. These results suggest that the overall risk of oak infection by SOD is rising.
Spikes in the estimated SOD infection level at certain locations are particularly noteworthy; for example, from 1 to 12 percent in the western part of the East Bay between Richmond and San Leandro, including distinct outbreaks discovered in El Cerrito, Kensington and Berkeley. The western slopes of the Santa Cruz Mountains in San Mateo County have also seen an increase in SOD infection rate (from 6 to 18 percent), which may make safeguarding recreational venues and ecologically important forest sites more difficult. In Sonoma County, the 2019 SOD infection rate was approximately double that of 2018, and in the same timeframe, Napa saw a fourfold increase in detection. Peninsula towns between Redwood City and Los Altos Hills had a very high infection rate (21.6 percent) with an expansion of outbreaks to the east and north.
Some additional key results that came from the 2019 SOD Blitzes include:
- Two tanoaks were positive for SOD in a state park east of Crescent City in Del Norte County, marking the first report of SOD for the county. This was an important finding because, until 2019, Del Norte was the only county free of the disease in the area between the vast California infestation and the Southern Oregon outbreak. The SOD Blitz finding does not have immediate implications for regulations, but regulations will be imposed once CDFA can confirm the finding.
- An extensive survey of San Luis Obispo failed to identify SOD; however, multiple trees were found to be infected in the southernmost canyon of Monterey County. Previously, this canyon had only provided positive findings from water monitored by UC Davis scientists, but not from trees.
- Although Humboldt County has a few significant SOD outbreaks, and Trinity County has a marginal SOD outbreak in its southwestern border, SOD Blitzes in tribal lands in Humboldt and Trinity counties did not yield any SOD positives.
- San Francisco parks, including the Presidio, were negative for a second year in a row, suggesting that disease management practices have been successfully implemented in the area.
- Several cases were identified in the northern neighborhoods of the City of Napa. No positives had been found in this area since 2011.
- All isolates of the pathogen belonged to the NA1 lineage, which is more easily treated and common in the region. This is good news because of uncertainty about the potential virulence of the EU1 lineage recently discovered in Oregon forests.
A sampling of other noteworthy 2019 SOD Blitzes results follow. More results are available on the websites and app:
- The first infected Bay laurel was identified a few miles east of the town of Mendocino (Mendocino County) along the Comptche-Ukiah Road.
- Multiple SOD positive trees were identified between Guerneville and Duncan Mills in Sonoma County. The Russian River area has long been known to be affected by SOD.
- An outbreak was identified in southwestern Petaluma, while infestations were confirmed in Bennett Valley, Santa Rosa and east of Rohnert Park.
- Multiple infestations were identified in Marin County, including the ones northeast of San Rafael, Larkspur, Woodacre, Mount Tamalpais, Marin City and north of Inverness.
- In the Peninsula, SOD was identified in Burlingame Hills, northern Woodside, Emerald Hills, Palomar Park, Portola Valley. In Los Altos Hills and Loyola, SOD positive trees were detected both East and West of Interstate 280. An outbreak was detected west of Saratoga.
- High levels of infection were identified all along Skyline between Bear Gulch Road and Highway 17, and on the western slopes of the Santa Cruz Mountains between Skyline and Pescadero.
- SOD was confirmed between Felton and Santa Cruz and between Aptos and Santa Cruz.
- In Monterey County, the chronic Big Sur outbreak was once again confirmed to be active, while the disease appeared also in drier areas of the Carmel Valley, where it had been absent for a few years.
The SOD Blitz program was funded in part by the U.S. Forest Service's State and Private Forestry Organization and by the Midpeninsula Regional Open Space District. It was also made possible by a collaboration with the California Native Plant Society, CalFire, the Humboldt/Del Norte and Sonoma County UC Cooperative Extension, the Sonoma County UC Master Gardeners, the U.S. National Parks, California State Parks, the East Bay Regional Parks, the San Francisco Public Utility Commission, Mid-Pen Open Space, the UC Santa Cruz Arboretum, Santa Cruz Open Space, the Santa Lucia Conservancy, the Karuk and Hoopa Nations, the Mendocino Botanical Garden, the City and County of San Francisco Parks and Recs Office, and Strybing Arboretum. Many individuals, who have generously devoted their time and efforts, have been pivotal for the existence and success of the program.
- Matteo Garbelotto: Leading the citizen science contagion
- First known cases of sudden oak death detected in Del Norte County
- SOD Blitz Project
- SOD Blitz map of results and summary table
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.
"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.
“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.
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.
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 firstname.lastname@example.org. 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.
Results of the 2015 Sudden Oak Death Blitz survey reveal coastal mountain infestations in areas such as Big Sur (19% infection), the Santa Cruz Mountains (13% infection), and western Sonoma County (12% infection) remain high despite an overall decline in infection rates from 4.4% to 3.7% across California's 15 infested counties.
Sudden oak death (SOD) symptoms have been seen in Alameda, Contra Costa, Humboldt, Lake, Marin, Mendocino, Monterey, Napa, San Francisco, San Mateo, Santa Clara, Santa Cruz, Solano, Sonoma and Trinity counties.
“Understanding the current disease distribution is key to preventing sudden oak death spread. Citizen scientists have been an invaluable help with this task over the last decade,” said Matteo Garbelotto, UC ANR Cooperative Extension specialist in the Department of Environmental Science, Policy and Management at UC Berkeley, who organizes the annual SOD Blitz.
Several new SOD outbreaks of note were identified during the blitzes. Two infected California bay laurel trees were confirmed near UC Berkeley's West Gate, a high-traffic, high-risk area with many heritage oaks. An infected California lilac shrub was found in the Presidio of San Francisco's (part of the Golden Gate National Recreation Area) southeastern quadrant. An infected California bay laurel tree was confirmed in Danville (eastern Contra Costa County) in an area where SOD had not previously been reported, and an urban park in Saratoga was found infested for the first time.
Nineteen citizen science-based SOD Blitzes (largest number of blitzes to date) were held this spring, two of which were new this year – one in Trinity County and one on Kashia Band of Pomo Indian land in Mendocino County. The 504 volunteers surveyed nearly 10,000 trees from San Luis Obispo County, north to Mendocino and Trinity counties. Each volunteer was trained to identify Phytophthora ramorum (the plant pathogen known to cause SOD) symptoms on California bay laurel and tanoak leaves. “Blitzers” had up to three days to collect and record locations of symptomatic samples, which were then sent to the Garbelotto lab for DNA analysis to determine the presence or absence of the pathogen.
Garbelotto is sharing results from the spring blitzes as well as new recommendations for SOD management at workshops being held around the Bay Area. Workshops will be held in Sebastopol on Nov. 3, in Berkeley on Nov. 4, and in San Rafael on Nov. 13. For details, see “Community meetings” at sodblitz.org.
For landowners in infested areas concerned about protecting their oak trees, Garbelotto will reveal his updated three-step SOD management plan. He will show them how to:
- Use the SODMap mobile app to help assess risk of oak infection (see sodmapmobile.org).
- Determine if California bay laurel trees near high-value oaks should be considered for removal (using a new buffer zone new chart - http://nature.berkeley.edu/garbelottowp/?page_id=2345).
- Apply phosphonates to high-value oak and tanoak trees to boost immunity (updated dosages and application frequencies at http://nature.berkeley.edu/garbelottowp/?page_id=2348).
Infection on California bay laurel and tanoak leaves indicates arrival of P. ramorum to an area, but true oak (California black oak, coast live oak, canyon live oak and Shreve's oak) infection typically requires a couple of years with wet conditions after pathogen arrival. Therefore, preventatively treating oaks to help ward off infection is best done when early indicator species first show symptoms, prior to oak infection and optimal conditions for the pathogen – cool and moist.
These surveys are made possible thanks to funding from the USDA Forest Service and the PG&E Foundation as well as help from the California Native Plant Society.
For more information on the workshops, go to sodblitz.org or contact Katie Harrell at (510) 847-5482 or email@example.com. For more information on sudden oak death and P. ramorum, visit the California Oak Mortality Task Force website at suddenoakdeath.org.
“Invasive insects, diseases and plant seeds can move on cut Christmas trees and other holiday greenery,” said Janice Alexander, UC Cooperative Extension forest health educator in Marin County. “These pests can escape out into backyards and neighboring forests to begin new populations, upsetting the balance of our native ecosystems. Proper purchasing and disposal of holiday greenery helps reduce that risk.”
Alexander recommends taking advantage of local tree recycling programs.
“You should not try to burn the wood indoors as fresh sap can create fire hazards,” she added, “and don't set the tree out in a backyard brush pile where pests and weed seeds could escape onto your property.”
“The most worrisome pests that might be traveling on Christmas trees or greenery this year include P. ramorum, pine shoot beetle and gypsy moth,” Alexander said.
The movement of some fresh trees is regulated. For example, Douglas fir trees are regulated because they are hosts for Phytophthora ramorum, which causes sudden oak death. The disease has killed millions of tanoak trees and several oak tree species in forests throughout California since the mid-1990s.
Pine shoot beetles, Tomicus piniperda, feed on shoots, stunting the growth of pine trees. Large populations of the insects can kill apparently healthy trees.
Gypsy moth, Lymantria dispar, attacks forests and landscape trees, including manzanita, western hemlock, Douglas fir and live oak. Gypsy moth caterpillars feed on hundreds of plant species and are capable of defoliating trees at an alarming rate. A single gypsy moth caterpillar can eat up to one square foot of leaves per day, according to the California Department of Food and Agriculture.
For more information about sudden oak death and forest health, visit Alexander's website at http://cemarin.ucanr.edu/Programs/Custom_Program816. More information about holiday greenery pests can be found at the USDA APHIS website and the Don't Move Firewood website http://www.dontmovefirewood.org/HolidayGreenery.
Millions of trees, including tanoaks, coast live oak, California bay laurels, and many other forest species have been killed by sudden oak death in coastal areas of central and northern California, and Oregon. The pathogen, Phytophthora ramorum, was first linked to the massive tree death in the mid-1990s.
David Rizzo, professor in the Department of Plant Pathology at UC Davis, and his research team are studying how the coastal forest ecology is changing since sudden oak death appeared, and why coast redwoods (Sequoia sempervirens) are subsequently so much more susceptible to fire.
It is the presence of the sudden oak death pathogen in forests that poses heavier fire risks for redwoods.
“If redwoods didn’t live in forests affected by the disease, they could withstand fires just fine,” says Margaret Metz, a postdoctoral research scholar working with Rizzo.
According to Rizzo, “The disease likely created more fuel for wildfires as dead tanoak branches fell. The loss of the oaks also would have decreased the amount of shade, drying out the forest and turning it into a tinder box, one not even redwoods could survive.”
A real key, though, is the finding that dead tanoaks, still standing, carry flames high into tree canopies, scorching the crowns of adjacent redwood trees. It’s this crown injury that is believed to have caused so many redwood trees to die in a number of fires that occurred in 2008.
Rizzo, noting that an increase in fire severity is resulting from climate change and global movement of species, says, “There may be all sorts of consequences, among them, dead and dying coast redwoods.”
- California's iconic redwoods in danger from fire and infectious disease. National Science Foundation report on Rizzo group’s work, August 2013
- The effects of sudden oak death and wildfire on forest composition and dynamics in the Big Sur ecoregion of coastal California. General technical report
- Ecology research article, Ecological Society of America
- California Oak Mortality Task Force website