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.
So why are oak forests important? Many would say they are a huge part of our county’s scenic landscape, but they also provide valuable habitat for more than 300 wildlife species and as many as 5,000 insect species. Oaks provide an abundant food source as well as cavities that house birds like the oak titmouse, and fallen logs and branches used by ants, beetles, salamanders and even frogs. Oak woodlands are simply teaming with life.
Where is your favorite spot to enjoy Sonoma County’s magnificent oak woodlands? Is it a stretch along your morning commute, a park you often visit, or perhaps the trees in your yard?
Oak trees are perhaps the single most iconic element of our landscape. So what do we know about them?
For starters, there are 10 different species in Sonoma County, and in many places the trees are blended together in an unusual way. While other counties boast high numbers of blue oak woodlands or Oregon oak woodlands, here scientists just scratch their heads and label many of our forest stands “mixed oak.” This diversity can be seen in the patchwork of greens in the forest canopy around places like Spring Lake.
Where they do carve out their own single-type stands, oaks can teach you something about the microclimate and soil type you are in.
The majestic valley oaks love the deep soils in our valley bottoms. Hike through the Laguna de Santa Rosa to get a good look at them. Their leaves are dull green, without sharp tips and deeply lobed. Blue oaks endure relatively hot and rocky locations. Look for them on inland ridges like those in Sonoma Valley above the town of Glen Ellen. Their leaves are blue-green, no sharp tips and shallowly lobed.
Black oaks are water lovers and enjoy shady canyons like those in Hood Mountain and Sugarloaf Ridge. Their leaves are large and sharply tipped, with deep lobes.
Oregon oaks take up where the valley oaks leave off on hillsides with fertile soils. They can be seen with the coast live oak rimming the meadows at places like Taylor Mountain. Leaves are bright green, lobed and not sharply tipped.
And finally there is our most ubiquitous oak, the coast live oak, which dominates the western portion of the county while holding its own in almost any setting. Its leaves are dark green, curved, with sharp little spines.
To make matters more interesting, many of Sonoma County’s oaks hybridize, creating another 12 versions of oak to inspire your appreciation for the wonders of nature. Annadel State Park is a good example of rampant hybridization between blue oak and Oregon oak.
Read more: | Sonoma Index-Tribune | Sonoma, CA
Meglenda Anderson, THE PRESS DEMOCRAT
A controversial ballot measure that would put a wrench in the longstanding timber-management practice of poisoning hardwood trees to make way for conifers was passed by voters Tuesday night.
Support for Measure V had garnered about 60 percent of the vote. The vote was 6,365 in favor and 4,249 against.Measure V is aimed at limiting the practice of poisoning unwanted hardwood trees, then leaving them to die in the forest. The practice is referred to as “hack and squirt” because it entails making a cut in a tree, then applying herbicide to the wound.
The measure declares it a nuisance to kill and leave standing for more than 90 days trees that are over 16 feet tall. It makes the person or agency responsible liable for damages the practice may cause to structures, water sources and telecommunication lines within 3,300 feet of the dead trees.
Proponents of the ballot measure say the practice has escalated in recent years, creating a dangerous fire hazard by leaving millions of dead trees standing in Mendocino County forests. Timber officials from Mendocino Redwood Company, the primary target of the ordinance, contend the fire hazard alleged by the measure’s proponents is overblown.
They say the practice of killing hardwoods, like tan oak, is crucial to restoring previously overcut and mismanaged forests to conifer production.
Source: Approval of Measure V in Mendocino County ends ‘hack and squirt’ | The Press Democrat
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