Major Infectious Disease Threatening Oak Trees in California

December 6, 2019 Updated: December 6, 2019
FONT BFONT SText size

Experts say that there is a serious, widespread disease threatening oak trees in northern and central California, and it’s getting worse.

A recent survey conducted by scientists from UC Berkeley found that the amount of oak trees infected by Sudden Oak Death (SOD) has nearly doubled since last year.

“The combination of a very, very wet year two years ago and a wet year this year would very easily explain the surge in infection rates,” Matteo Garbelotto, director of UC Berkeley’s Forest Pathology and Mycology Laboratory, told The Epoch Times.

The disease is estimated to have killed more than 50 million oaks in the region over the last twenty years.

“You can think of the disease a little bit like malaria,” Garbelotto continued. “It’s actually not spread by oaks. It’s spread by other trees, in particular the California bay laurel. Like mosquitos carry malaria, bay laurels carry Sudden Oak Death. And then if a bay laurel grows next to an oak, then the infection jumps on the oak. The oak doesn’t spread the disease, so it’s very complicated.”

“It is unsettling,” Susan Frankel, a plant pathologist for the Pacific Southwest Research Station, told The Epoch Times. “This is a non-native pathogen.”

According to Chris Lee, a forest health specialist and chair of the California Oak Mortality Task Force, the fact that this disease is non-native is one of two explanations for its proliferation.

“The pathogen that causes sudden oak death has spread so rapidly partly because it is an introduced (non-native) pathogen and partly because it is dispersed through the air,” Lee told The Epoch Times.

“Since these trees haven’t evolved alongside this pathogen for millennia, they haven’t evolved specific defenses (such as chemicals or specialized anatomical features) against them,” he added. As a result, the pathogen’s “aggressiveness [has been] enabled.”

Frankel explained that the appearance of the disease isn’t exactly sudden.

“In California, the disease was first noticed in the mid-1990s. By [that] time … it was already very widespread [and] the damage was very extensive. It would have taken an unprecedented effort to control it. In Oregon they did try to control it, and that didn’t work out.”

According to Garbelotto, there are three identifiable risk levels associated with SOD.

“The first one, obviously, is that the tree will be dead,” he said. “The second [most important level] is the fact that the trees that are infected … fall down very easily, and the process of falling down can hurt people and property and so forth.”

The third risk level involves the pronounced dryness of the tree, which can foster the spreading of wildfires, because they “tend to burn very hot.”

“It’s a problem because it generates these hot spots for fires that are very, very difficult to handle,” Garbelotto said. “Basically, firefighters move away from these situations because the fire’s too hot.”

While there is no single management technique proven to eliminate the infection from a forested area, there are preventative precautions that can be taken, say experts.

The most effective means of combatting SOD is to remove all small- or medium-sized bay laurels that are within close proximity—about ten yards—to oak trees.

When it comes to particularly valuable oaks, Garbelotto recommends an environmentally-friendly chemical treatment that makes the oak more resistant by strengthening its immune system against pathogen attacks.

The tanoak tree also poses a vital threat to oak trees because it can spread the disease as well: “It’s almost like a bay and an oak together,” Garbelotto said.

“It’s very unlikely that we’ll find a silver bullet for completely alleviating the impacts,” Lee said. “But we should continue to try to protect our most vulnerable forest stands, reduce the impacts as much as possible for affected communities, tackle the heightened fuel loads, hazard trees, and other damage that the pathogen can cause in forests, and continue to look for solutions that enable us to restore affected forest stands.”

The mobile app SODmap, available through the UC Berkeley website, is providing assistance in terms of determining the distribution and presence of the disease.