A deadly fungus killing oak trees along the coasts of central and southern California appears to be creeping farther east, with one case recently confirmed in Calaveras County and others under investigation in Tuolumne County.
Foamy bark canker was discovered Sept. 22 by Foothill Sierra Pest Control in an interior live oak on a property in the Greenhorn Creek neighborhood in Angels Camp. The disease has killed thousands of coastal live oaks in California since late 2012.
“It’s bad enough we’re losing our pines,” said Jim Tassano, owner of Foothill Sierra Pest Control. “We don’t want to lose our live oaks.”
Tassano said he “had never seen anything like it” when he first inspected the oaks, so he called upon experts for help.
The fungus is spread by the western oak bark beetle, a separate species from those that have killed more than 66 million pines and counting in the Sierra Nevada.
Much like their conifer-eating counterparts, the beetles colonize parts of oaks that are severely stressed or dead by lack of water, damage, disease or other factors. Adult beetles burrow through the bark and excavate tunnels in the sapwood, where they lay their eggs.
An article written by Scott Oneto, the University of California Cooperative Extension farm advisor for Tuolumne, Calaveras, Amador and El Dorado counties, stated the fungus is carried on the backs of the beetle and deposited into a tree’s vascular system.
Symptoms of the disease include foamy liquid oozing from the trunk and branches. Small entry holes about the size of pencil lead can be seen where the beetle burrowed into the bark, the article stated.
Tassano asked Oneto to check out the oaks in Angels Camp. Oneto had previously confirmed one case on private property in El Dorado County in July. Prior to that, the disease was largely confined to coastal counties.
Oneto took samples from the Angels Camp tree and sent them to researchers at UC Riverside, who published the first scientific paper on the relatively new disease in 2014. The results came back earlier this month positive for foamy bark canker.
“Unfortunately, we don’t have a lot of great control recommendations at the moment, because this is a fairly newly identified pathogen,” Oneto said.
Oneto said the fact that it’s spread by bark beetles indicates that lack of water is a major factor in the disease’s spread.
How the beetle made the jump from the coast to the foothills is unclear, but Oneto also said the disease can be transmitted by beetles in cut firewood.
Irrigating oaks is one way to possibly make them healthy enough to fight off the infestation, according to Oneto.
“We know that drought-stressed trees are more susceptible to bark beetle attacks,” he said. “If someone has a tree around there home and it’s severely drought stressed, that’s one of the first recommendations I would give them.”
The infected oaks Oneto has investigated thus far in Placerville and Angels Camp were all on landscaped property, suggesting other stressors than the drought alone may be at play in those cases.
Still, Oneto expects more cases to crop up. He’s received calls in the past couple days about oaks that appear to be show symptoms of the disease, but he has yet to confirm those cases.
“I have a feeling we’re going to see more cases of foamy bark canker in landscaped settings first,” he said. “That’s a concern, because people have a lot of oaks around their homes.”
Oneto said he’s informed Tuolumne County Master Gardeners volunteers about the disease and how to look out for it.
Despite the scary prospect of a new type of beetle killing more trees, Oneto said he’s optimistic it won’t spread as fast as the outbreak that’s currently attacking pines throughout the Sierra Nevada.
“I’m going to hope that we’re going to get out of the drought with some very prolific rains this winter,” he said. “Once these trees get back to a healthy state, I think it’s going to be something we won’t have to worry about all that much.”