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Posts Tagged: sudden oak death

Sudden oak death moving to urban areas; 3 steps to protect oaks

Doug Schmidt, standing, and Matteo Garbelotto examine a bay laurel on the UC Berkeley campus.
Drought is decreasing but not defeating the pathogen that causes sudden oak death, according to a citizen science-assisted survey conducted this spring by a UC Agriculture and Natural Resources forest pathologist.

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.

These bay laurel leaves show P. ramorum symptoms.
“In an effort to protect habitat restoration in the Presidio, we are working to strengthen Best Management Practices to prevent the spread of SOD based on the Garbelotto lab recommendations,” said Christa Conforti, integrated pest management specialist at Presidio Trust in San Francisco. “In partnership with UC, the National Park Service, and the Golden Gate National Parks Conservancy, we are developing a Phytophthora prevention, detection and control strategy, which includes active participation in SOD Blitzes.”

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.

The SODMap mobile app shows a map of sampled trees.
SOD management workshops

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

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:

  1. Use the SODMap mobile app to help assess risk of oak infection (see
  2. Determine if California bay laurel trees near high-value oaks should be considered for removal (using a new buffer zone new chart -
  3. Apply phosphonates to high-value oak and tanoak trees to boost immunity (updated dosages and application frequencies at

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 or contact Katie Harrell at (510) 847-5482 or For more information on sudden oak death and P. ramorum, visit the California Oak Mortality Task Force website at


Posted on Friday, September 25, 2015 at 11:38 AM

Recycling Christmas trees helps curb the spread of pests

Recycling Christmas trees helps prevent the spread of pests.
If you have a real Christmas tree, University of California pest management experts ask that you to recycle the tree to prevent the spread of insects and diseases that may harm our forests and landscape trees.

“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.

Sudden oak death symptoms are shown here on Grand fir. Photo by Gary Chastagner.
“Many municipalities and service organizations offer this service right at your curb,” she said. “If you aren't able to find or use this option, take the tree to your local solid waste facility, dump or landfill. This will keep any pests that might be in the tree from spreading and the landfill uses the material as cover.”

“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 can stunt and even kill pine trees.
Pine shoot beetle and gypsy moth are not currently in California, but they could damage the state's Christmas tree plantations and forests if they were to become established.

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. 

A single gypsy moth caterpillar can eat up to one square foot of leaves per day. Photo by Roger Zerillo.
“According to the Don't Move Firewood website, Christmas trees are generally deemed safer than firewood in terms of invasive pests,” Alexander said. “However, safe disposal of trees is still important.”

For more information about sudden oak death and forest health, visit Alexander's website at More information about holiday greenery pests can be found at the USDA APHIS website and the Don't Move Firewood website






Posted on Friday, December 19, 2014 at 8:35 AM

Coast redwoods increasingly susceptible to fire damage

Fire consumes a once-healthy California redwood tree. (photo: USFS)
California’s renowned coast redwood trees, previously believed to be fireproof, are now more than four times more susceptible to wildfire injury in coastal forest areas infested with the sudden oak death pathogen. These redwoods are now as susceptible to wildfires as other trees.

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.

Professor David Rizzo, UC Davis.
An initial explanation for the higher redwood mortality following wildfires is heavier fuel loads (such as fallen, dead branches from tanoaks) in forests affected by sudden oak death. Tanoak, Notholithocarpus densiflorus, is the primary host dying from sudden oak death and the main source of pathogen inoculum.

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.

Dead tanoaks in a redwood forest in the scientists’ California study area, pre-fire. (photo: Kerri Frangioso/UC Davis)
“Humans are causing widespread changes throughout our world, including greater wildfires related to changing climate and from increasing infectious disease due to more modes of transportation,” said Sam Scheiner of the National Science Foundation, which funded some of this research.

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.”

Additional information:

  • 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
Posted on Wednesday, September 4, 2013 at 7:21 AM

Community effort beats back sudden oak death in Humboldt County

From left: Mark Rodgers, Julie Lydick, Pete Angwin, Rizzo, Valachovic, Phil Cannon, Ed Burton, Stephen Smith, Jack Marshall, Chris Nota and Russ Henly
Sudden oak death is a misnomer because it doesn't fell a tree like a lightning strike nor does the disease limit itself to oaks. Nonetheless, the moniker has stuck and UC scientists remain committed to containing the culprit. 

UC, federal and state agencies and landowners in Humboldt County recently received national recognition for their collaborative efforts to halt the spread of sudden oak death. Kathleen Merrigan, U.S. Department of Agriculture deputy secretary, praised the partnership during her visit to Davis on May 16.

Yana Valachovic, UC Cooperative Extension advisor in Humboldt County, and Dave Rizzo, professor in the Department of Plant Pathology at UC Davis, were joined at the USDA offices in Davis by their partners from USDA Forest Service, CAL FIRE and the Natural Resources Conservation Service to accept the Two Chiefs’ Partnership Award. Merrigan presented the award on behalf of the “two chiefs” – the head of NRCS and the head of the Forest Service.

For me, it was a pleasure not just to see Yana’s efforts rewarded, but also to see Dave Rizzo. About a decade has passed since the days I was on the phone and email almost daily forwarding reporter requests for interviews to the UC Davis plant pathologist. Rizzo was first to identify Phytophthera ramorum as the pathogen that causes sudden oak death in 2000.

Matteo Garbelotto of UC Berkeley demonstrates sudden oak death diagnosis and treatment for members of the media at the Berkeley campus.
As tens of thousands of California's beloved oaks fell to the disease, Rizzo and his colleague Matteo Garbelotto, UC Cooperative Extension specialist at UC Berkeley, an expert in forest pathology, were thrust into the limelight.

Although SOD doesn't make the news as frequently as it did in the early 2000s, it continues to spread. Garbelotto’s "SOD Blitz," his annual survey, found in 2011 that the rate of infection in trees between Napa and Carmel had grown as much as three times the rate of the previous year.

Since the disease was first reported in Marin County in 1995, it has been found in 14 coastal California counties and killed over 5 million tanoak, coast live oak, California black oak, Shreve oak and canyon live oak trees, according to the Forest Service.

UC Cooperative Extension employees were surprised in the spring of 2010 when routine  monitoring near the mouth of Redwood Creek in Humboldt County detected P. ramorum in leaf samples. It meant that trees were infected somewhere in the 200,000-acre watershed – more than 50 miles from the nearest known infestation and farther north than the pathogen had ever been detected in California.

UCCE staff coordinated a swift management response, embarking on the largest SOD management project ever to occur in California. They collaborated with the Forest Service, NRCS, CAL FIRE, tribes, local timber companies and private landowners to remove infected plant material. Rizzo pitched in with diagnostics for the project and matching funds to qualify for a federal grant.

From left, UCCE staff research associate Chris Lee, NRCS forester David Casey and Yana Valachovic inspect the treated area for signs of sudden oak death.
“We’ve been closely monitoring the disease for years and anticipating a scenario like Redwood Valley, so we were ready to take action and respond quickly,” said Valachovic, a forestry expert.

It’s still not clear how the pathogen got to Redwood Valley, said Valachovic, but it could threaten the dense tanoak forests of the surrounding area, killing trees and leaving behind dry brush, which could fuel wildfire. 

Landowner support has been critical to the success of the project, according to Valachovic. More than 20 landowners in the valley have allowed monitoring and treatment activities on their properties, recognizing that their cooperation may keep the disease from spreading to other areas.

The first phase of treatment is currently wrapping up, and UCCE is beginning to monitor project efficacy and watch for spread of the pathogen beyond project boundaries. The Yurok and Hoopa tribes will be paying close attention to this effort, as they are only a ridge away from the infestation. 

“Oaks are an important part of our culture and history, and we will do what we can to keep sudden oak death out of our forests,” says Ron Reed, a Yurok tribal forester.

The OakMapper app and website enable hikers and others to report SOD.
The Redwood Valley project highlights the benefits of people working together. If you would like to report sudden oak death, you can download the OakMapper smartphone app or submit reports at the OakMapper website. The website also features a map showing suspected and confirmed cases of sudden oak death.

Scientists, managers, regulators and policymakers will gather June 19-22, 2012, to discuss the latest news about the disease at the Fifth Sudden Oak Death Science Symposium in Petaluma.

For more information about sudden oak death disease, visit the California Oak Mortality Task Force website at  


Posted on Wednesday, May 30, 2012 at 12:01 PM

Sudden oak death may increase wildfire fuel

SOD killed these trees, leaving dry fuel for a fire.
Sudden oak death (SOD) has been spreading among trees throughout coastal California and Oregon for the last 15 years. In that short time, the disease has infested 10 percent of California’s at-risk habitat and killed over a million tanoak and true oak trees, raising major concerns about the potential impacts of further pathogen spread. The disease is caused by the non-native pathogen Phytophthora ramorum.

Research by UC Cooperative Extension staff in Humboldt County shows that infection and oak mortality are only the beginning of the story, as the disease may increase forest fuels and put infested stands at higher risk of severe wildfire.

UC Cooperative Extension forest advisor Yana Valachovic, with assistance from Humboldt State University’s Forestry Department and CAL FIRE, found that in Douglas-fir-tanoak forests where high hardwood mortality is related to SOD, fuels can build up to hazardous levels on the forest floor over time. Their research documented fuels buildups in infected areas that could increase a wildfire’s flame length by 3 to 4 feet and double a wildfire’s rate of spread, depending on how much time has elapsed since initial infection.

The arrangement of dry leaves and dead branches pose serious challenges to firefighters in infested stands.
Not only does SOD alter fuel quantity in these forest types, but it can also affect moisture levels and the arrangements of fuels, posing serious challenges to firefighter response in infested stands. The disease drastically reduces the moisture content of foliage, and after trees die, they remain standing with dry, dead leaves for a few years – greatly increasing the likelihood of crown fire under extreme weather conditions.

Likewise, the increased fuels on the forest floor can take a long time to break down, posing a long-term fire hazard and additional risks to firefighters.

“The disease creates a hazardous fuels situation that is passed on to firefighters during wildfire," says Valachovic. "They must combat blazing downed trees, patches of increased winds and fire behavior, and other physical and logistical obstacles.”

Hugh Scanlon, chief of CAL FIRE's Alder Conservation Camp, helped co-author the recent paper with Valachovic and others. 

"In many cases, modeled wildfire conditions in sudden oak death affected forests exceed safety thresholds for handcrews, calling for changing suppression tactics and strategies," Scanlon says. "This can mean more heavy equipment, aircraft use, indirect lines and more area burned with higher intensity.”

Sudden oak death is still a relatively new disease in California, and the long-term ecological consequences of SOD infection and spread are largely unknown. However, this research shows that fuels are one of the major issues associated with the disease, and will require increased attention and management in coming years. For more information about this study, see the full paper, which was published in the journal Forest Ecology and Management (

To see a map showing the locations of sudden oak death in California, go to At the website, you can also download the Oakmapper iPhone app to help UC scientists monitor the disease by reporting suspected cases of sudden oak death. 

Posted on Wednesday, February 15, 2012 at 6:56 AM
Tags: sudden oak death (6), wildfire (2)

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