Eliminating infected North Bay oak trees may spread invasive beetle
SANTA ROSA -- An invasive pest has been found in oak trees in a west Santa Rosa neighborhood that has officials and tree experts sounding an alarm. While the number of dying, infected trees is on the rise, removing them may make the problem even worse.
The majestic oak trees that line the highway in rural Sonoma County give the area a timeless feel but, in Zack Fresco's back yard, a giant pile of wood under a plastic tarp is all that is left of a 175-year-old tree.
"It does break my heart," Fresco said. "One of my neighbor's trees came down in a storm and my kids and I went and sanded the trunk so we could count the rings and we got 360 years. Think about what was happening then. They're from a different era."
What killed Fresco's tree was no storm. It was an invasive beetle called the Mediterranean Oak Borer. The bug, which is prevalent in a number of European countries including France, was first discovered in California about six years ago in the Calistoga area. There is a suspicion that the borers may have hitched a ride to Northern California on some imported wood used for making wine barrels.
"They cannot fly overseas. They must have been brought to California or this area by some kind of contaminated plant material," said UC Davis plant pathologist Dr. Akif Eskalen.
Now, Dr. Eskalen says the beetles are taking advantage of how weak many trees are after three years of extreme drought.
"If we don't have that beetle, would that drought work to kill a hundreds-year-old tree? It may not," said Dr. Eskalen. "They cause stress on the plants but they don't kill the plants. But these guys -- the secondaries -- when they come, they kill them."
It may seem like the solution is to remove the infected trees but Merlin Schlumberger, the master arborist who identified the borers in Fresco's tree, said preventing further spread of the pest poses a difficult dilemma for tree cutters.
"Typically, the tree service would remove it, take away the wood, take away the wood chips. That's what tree services do. But, with this, once we move the wood, we might be infecting a new site with this wood and the beetles coming out and we're starting to see that. New sites are popping up with new dead trees here and there," Schlumberger explained.
For now, the cut-up tree remains under a plastic cover. The hope is that, after a few months, the sun's heat will kill the trapped pests. It's still just an experiment and Fresco has set up a trap nearby to monitor whether any borers escape. Meanwhile, Schlumberger wonders what this may mean for the future of the area's picturesque oak trees.
"If it keeps spreading, which it probably will, it's not good news," he said. "I don't think it's the kind of thing that will make them extinct but those of us who care about valley oaks, it's probably the most alarming thing I've encountered."
Now that the borers have reached the residential areas of west Santa Rosa, the fear is it will be much easier for them to spread. They can fly but they don't typically travel very far and the idea of solarizing every dead tree with plastic seems infeasible. So, Schlumberger is urging quick action. He thinks the county should identify a site, away from uninfected oaks, to create a quarantine zone to give tree cutters a place to dispose of infested wood.