It is the forgotten killer when compared to our increasingly frequent climate calamities, but the virulent pathogen known as sudden oak death remains active and is spreading death so fast it could destroy California’s coastal forest ecosystem, UC Berkeley scientists reported Thursday.
The deadly microbe has now established itself throughout the Bay Area and has spread along the coast from Monterey to Humboldt County, according to a study of 16,227 trees in 16 counties in Northern California.
Millions of coast live oak and tan oak trees have withered and died over the past quarter century, leaving acres of kindling for wildfires, but the outbreak this year was one of the worst. Oak trees have historically been abundant in California and southwestern Oregon, with hundreds of millions of them stretching all the way to Baja California.
The rate of trees infected almost doubled in 2019 — from 3.5% to 5.9% — and was 10 times higher in some places compared with the 2018 survey, said Matteo Garbelotto, the director of the UC Berkeley Forest Pathology and Mycology Laboratory, which tested leaf samples taken by 422 volunteers.
Now that the North Coast is finally drying out from an unusually wet winter, concern is growing over the potential rapid spread of sudden oak disease, renewing calls for the public’s help tracking the deadly forest pathogen.
“Now is when we might expect the pathogen to take off a bit,” said Kerry Wininger, a UC Cooperative Extension staffer in Santa Rosa.
Wininger is a local organizer of annual sudden oak death surveys known as the SOD Blitz. This year’s survey occurs from April 25 to 28 across Sonoma and Mendocino counties. Organizers are hoping for a good turnout of volunteers, who will become educated spotters and collectors to help scientists slow the disease’s spread.
A relatively dry winter in 2017-18, coupled with the attention paid to devastating wildfires, appear to have dampened public concern over sudden oak death. But experts say conditions are ripe now for a resurgence of the disease. In addition, there’s heightened worry about a new, more virulent strain of the pathogen gaining a hold on the North Coast and causing more devastation.
Wininger said one of the highlights of this year’s surveys is the unveiling of a new test for the European strain in time to possibly thwart its spread. The new strain has been detected in Oregon.
“We want to nip it in the bud, if it’s here,” Wininger said.
Phytophtora ramorum, the pathogen that causes SOD, most often is spread by water droplets blowing from the leaves of infected bay laurel trees. There is no cure, only preventative measures or destroying oak and tanoak trees that succumb to the pathogen.
A dry winter curtailed the presence of a deadly forest pathogen this year in Sonoma County and 13 other Northern and Central California counties, but experts still expect the oak-killing disease to spread and warned landowners to be vigilant.
Since the mid-1990s, sudden oak death has killed up to 50 million trees from Big Sur to southwest Oregon and is entrenched in the woodlands, spreading rapidly after wet winters and slower during dry years.
“It’s constant, it’s emerging,” said Richard Cobb, an assistant professor of forest health at Cal Poly San Luis Obispo. “It’s probably going to get a lot worse.”
Cobb said Monday he’s about to publish his estimate of tree mortality, 90 percent of which are tanoaks and most of the rest coast live oaks. Another 100 million trees may be infected by the insidious pathogen that typically takes one or two years to produce symptoms in the infected trees, he said.
The pathogen can be spread by human footprints and nursery plants, but in nature it rides on water droplets blown from the leaves of bay laurel trees, a host species that abounds among the oak and tanoak trees susceptible to the disease.
Guy Kovner, THE PRESS DEMOCRAT
Rejuvenated by two straight wet winters, the insidious pathogen that has killed more than 3 million trees in Central and Northern California in the past two decades reached a record level of infection this year, including major gains in Sonoma County.
The spread of sudden oak death could further transform North Coast forests already ravaged by drought and altered by climate change, increasing their vulnerability to catastrophic fire.
The lethal pathogen is spread largely by wind-blown water droplets and resides in bay laurel trees without harm but can infect and ultimately kill four species of oaks, the fire-resistant native hardwoods that cover coastal ranges and inland valleys and hillsides. Their displacement, in favor of bay trees and conifers, could raise fire risks across the region.
“If you’ve had sudden oak death for 20 years, my guess is the forests will be worse off,” said Matteo Garbelotto, director of the forest pathology and mycology laboratory at UC Berkeley, which oversees the annual sudden oak death survey.
Results of the latest survey showed a 10-fold increase over 2015 — from 3.8 percent to 37 percent this year — in the sudden oak death infection rate in an area that includes Healdsburg, Santa Rosa, Sonoma and Petaluma. That level of infection, which stunned researchers, was matched or exceeded in only three other parts of the 17-county survey area.
The infection rate doubled north of Healdsburg and increased slightly less west of Highway 101, where the infection is already rampant in the hills west of Sebastopol.
Read more at: Sudden oak death rampant in Sonoma County after two wet winters, raising longterm fire risks
People who want to participate in this weekend’s local blitz are asked to sign up online at ucanr.edu/blitz2016 and to start by attending an hour-long training session Saturday morning at four locations in Santa Rosa, Graton, Cloverdale and Sonoma (see the website for details).
Spring rains brought relief to a drought-weary region, filling North Coast reservoirs and farm ponds and turning grassy hills a glorious emerald green.
But the wet, sometimes windy weather was also ideal for Phytophthora ramorum, the insidious pathogen that causes sudden oak death, a disease that has killed more than 3 million trees in coastal forests from Monterey to Humboldt counties since 1995, when it was discovered in Marin County.
The pathogen can be spread by human footprints and nursery plants, but in nature it rides in water droplets blown from the leaves of bay laurel trees, a host species that abounds in close proximity to the oak and tanoak trees that sudden oak death kills.
California’s four-year drought slowed the disease’s spread considerably, but officials are wary of a widespread rebound, including Sonoma County, owing to a comparatively soggy spring. Santa Rosa has recorded 12.5 inches of rain since March 1, compared with 1.5 inches in the same period last year.
“We think we’ll see a bump this year,” said Lisa Bell, the county’s sudden oak death program coordinator. “We want to see what the pathogen does coming out of a drought.”
The means for that assessment is the SOD Blitz, an annual volunteer effort organized by the UC Berkeley Forest Pathology and Mycology Lab. More than 40 people have signed up for the Sonoma County blitz on Saturday and Sunday, and Bell said she’s hoping for many more volunteers who will be trained to collect samples — primarily bay leaves — that will be analyzed at the Berkeley lab.
An epidemic of the tree disease “sudden oak death” has surged beyond control in California, a new study shows.
The computer model used in the study published this week in the Proceedings of the National Academy of Sciences took into account topography, weather and factors like funds available to fight the extremely contagious disease. It has killed millions of trees along the Northern California coast since it emerged in 1995.
The study suggests that the disease is spreading too fast to eradicate statewide, saying it will accelerate after 2020 when it is likely to flourish in California’s northwestern corner, where conditions are perfect for it.
Had the state begun fighting the disease in 2002, it may have been possible to eliminate it, the study says.
Critics have faulted the state and federal government for failing to take such stronger actions, the Los Angeles Times reported.
But the report is not entirely hopeless, offering recommendations for fighting the disease on a small scale to slow its growth by focusing on restoring small local forests.
Read more at: Study: Sudden oak death might be unstoppable in California | The Press Democrat
Guy Kovner, THE PRESS DEMOCRAT
Four years of drought have slowed the spread of sudden oak death to its lowest level in a decade, but western Sonoma County remains one of the hot spots in the 15 infested counties from Monterey to Humboldt, and when rain comes again the tree-killer will resume its rampage through Northern and Central California woodlands.
Analysis of more than 2,100 bay laurel tree leaves sampled during an annual citizen-powered survey last spring found a 3.7 percent estimated rate of sudden oak death infection, down from 4.4 percent in 2014 and possibly the lowest level since the disease erupted in 1995.
“I think we’re at the bottom of the infection rate,” said Matteo Garbelotto of the UC Berkeley Forest Pathology and Mycology Lab.
Drought conditions thwart the spread of sudden oak death, which largely depends on wet, windy weather to blow infectious spores from bay laurel trees, which host the pathogen, to oak and tanoak trees that die within a few years of infection.
Predictions of a strong El Niño weather pattern this winter could mean heavy rains for the North Coast. And when rain starts falling again, the as-yet unstoppable tree-killer will renew its assault, Garbelotto said.
“We know the sudden oak death pathogen can respond readily to wet conditions,” he said.A relatively wet climate, even during the drought, explains why west Sonoma County had an estimated 12.6 percent infection rate this year, up from 7.1 percent in 2014, he said.
Read more at: Drought slows spread of sudden oak death in | The Press Democrat
To protect the majestic centuries-old oaks at Jack London State Historic Park, state workers have this week begun cutting down invasive vegetation and bay laurel trees known to harbor sudden oak death, which has killed millions of oaks and tanoaks throughout Northern California.
As oak trees have died and toppled from the disease, canopy openings have widened at the park in Glen Ellen. That has let more light seep through some areas of the forest, fueling the growth of dense and more flammable plants, according to environmental officials.
Chainsaws and shears in hand, nearly a dozen workers with the California Conservation Corps made their way Tuesday up a section of the park near the Wolf House ruins to tear out broom and other brush that could act as “ladders,” allowing flames to climb onto tree canopies during a fire. They navigated their way around dead oak trees and poison oak to get to young bay laurels that threaten tanoaks and black and coast live oaks, which are more “vulnerable” to sudden oak death, according to Cyndy Shafer, a senior environmental scientist with California State Parks.
“We’re definitely not removing all of the bay trees. It’s very targeted and strategic,” Shafer said about the $150,000 project, funded by the state and aimed at reducing the fire risk and spread of the disease in the oak-dominated section of the forest.
“It’ll make it less inviting for sudden oak death,” she added. “(But) we will not be removing any mature, healthy trees.”
Dozens of volunteers are expected to comb Sonoma County woodlands in two weeks looking for the telltale signs of a tree killer.
They will be hunting for discolored leaves on bay laurels, evidence that those trees harbor the sudden oak death pathogen, which has infected more than 105,000 acres in the county.
Sudden oak death, discovered in Marin County in 1995, has killed more than 3 million tanoak and oak trees in 15 counties from from Monterey to Humboldt, according to UC Berkeley’s Forest Pathology Laboratory.
Taking advantage of what is expected to be another dry spring, the lab is focusing its seventh annual Sudden Oak Death Blitz on pinpointing the bay trees that are “reservoirs” of the pathogen, a fungus-like microbe called Phytophthora ramorum.
via New effort to track Sudden Oak Death in Sonoma County | The Press Democrat.
Sudden Oak Death Blitzes will be conducted from now through the end of May in the greater San Francisco Bay Area, with the Sonoma County blitz on April 19 and 20.
Sonoma County volunteers are expected to attend one of four training sessions April 19. The classes will last about an hour, followed by surveying and sampling trees that day and the next.
The classes are at:
• Sebastopol Center for the Arts, 282 South High St., Sebastopol, 9 a.m. to 10 a.m.
• Spring Lake Park Environmental Discovery Center, 5585 Newanga Ave., Santa Rosa, 9 a.m. to 10 a.m.
• Cloverdale Historical Society, 215 N. Cloverdale Blvd., Cloverdale, 11 a.m. to noon.
• Sonoma Community Center, 276 East Napa St., Sonoma, 9 a.m. to 10 a.m.
For more information on the classses, contact Lisa Bell, Sonoma County’s sudden oak death program coordinator, at email@example.com.