From Mendocino County Public Broadcasting, this is the KZYX news for Monday, October 7th. I'm Elise Cox. A deadly beetle that's been killing valley oaks in Napa and Sonoma Counties for several years now has made its way to Mendocino County. Michael Jones, the area forestry advisor with the University of California Cooperative Extension, sounded the alarm about the Mediterranean Oak Borer at the recent board of supervisors meeting.

Confirmation was in Hopland, then the found trees, the preferred host of this insect is is the white oaks, so valley oak coast excuse me. Valley oak, blue oak, and Oregon white oak. Confirmed infestations Hopland along the one one quarter south of Ukiah and in Potter Valley is pretty heavily infested.

As the name suggests, the Mediterranean Oak Borer is native to Mediterranean countries including Europe, the Middle East, and North Africa. The first beetle infestations were observed in Napa County in 2019 with Calistoga being a primary location. The beetle is also active in Lake and Sonoma Counties. According to the University of California's Department of Agriculture and Natural Resources, the adult female beetles tunnel into trees, usually at points where the bark is thin or cracked, leaving entry holes measuring around 1/16th of an inch. Beyond the entry point, the tunnels expand into branching galleries where the beetles cultivate gardens of fungal spores that are their primary food.

In Napa County, the beetle has been observed to colonize trees from the top down, sometimes starting from branches high in the canopy, and then as a population slowly expands reaching massive densities in the lower trunk. The beetle is not known for this behavior in its native habitat.

Certainly gonna be a huge challenge in urban spaces where valley oaks are important, urban forest trees and, you know, it's a pretty rapid killer of large valley oaks. So it's gonna be a pretty challenging condition or issue to deal with moving forward.

Supervisor McGourty asked about the characteristics of the trees the beetle was targeting.

So looking at this past, how how would you assess it? Is it virulent? Is it going after damaged or, weak trees or where is it on the scale of aggressiveness?

Yeah, that's a really good question. We're still trying to tease that out. At this point, it appears to be a pest of stressed trees, so it's kind of taking advantage, we call it secondary pest, where it's taking advantage of our heavily stressed trees. The problem with that is most of our urban trees are heavily stressed, and then because of drought, fire and other things, we're seeing kind of widespread landscape scale, stress and oaks in particular, and it's popping up in a lot of different systems. You know, it's a different management challenge in urban spaces where large value oak are high value for the aesthetics, for their property value, and recreation, they present huge hazards and because the limbs break and the trees are gonna die and some risks.

In the wildland spaces, it's more of an ecological alteration. So it varies depending on what trees you're talking about and what your kind of management goals and objectives are.

I guess following up on that too, so do we see it in young trees that are actively growing or is it more more older use that?

We see it in older kind of the old, decadent Valley Oaks, the ones that we all love. We see it in younger trees that are stressed, so drought stressed or fire stressed. We're still I mean, we've only just we detected this insect 3 years ago, and we're still really trying to understand its potential impact.

Thank you. Supervisor Haschak?

Thank you for that report. You know, we the information shows that we had like 1,300,000 dead trees in Mendocino County and this will add to that problem. Do you think that this is accelerated because of the drought we had or climate change or and what is the tendency to move towards other types of trees, the conifers and such?

So this particular pest is host specific to the white section of oaks, and valley oak is its preferred host tree. In Oregon where it's also been introduced, Oregon white oak is its preferred host, so it kind of shifts within that white section based on the availability of host material. It's not gonna cross over to conifers. It's a ambrosia beetle, which is like a really tiny version of a bark beetle, but it's not going to have the same because hardwoods have a little bit of a different defense mechanism than conifers, we're not going to see the same kind of exponential growth and increase in mortality that we see with conifers, kind of rapidly following drought or fire where we see explosions in bark beetle populations and extensive decline in mortality. This is going to kind of be, a buckshot mortality event where we're going to see clusters of trees dying across the landscape at different rates and at different concentrations and at different numbers.

So it's gonna not be kind of a pulse mortality event, but more of like a continuous decline and, you know, new trees will keep dying every year pretty much moving forward.

The main thing you can do to protect Mendocino's oak trees is to avoid moving infested firewood. The forest service strongly urges you to, quote, buy it where you burn it. Read more at www.firewood.ca.gov. If you suspect a Mediterranean oak borer is damaging a tree, please contact your county agricultural commissioner's office or the California Department of Food and Agriculture. The pest hotline is 180-049118 99.

That's 1-800-491-1899. You can also report a pest at www.cdfa.ca.gov/plant/reportapest. You can also find these links with our story at kzyx.org along with pictures of the female beetle and the damage it does to a tree. For KZYX news, I'm Alyce Cox. For all our local stories with photos and more, visit kzyx.org.

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