MOB In Lake County

Vandervort facilitates RRA, established in 2018 in response to Lake County’s devastating wildfires. He opened his presentation by reaffirming the RRA’s mission: “to coordinate local government efforts, provide low- to no-cost risk reduction programs, secure funding for resilience initiatives and offer educational resources to help Lake County residents better assess and manage risks.” He emphasized that the RRA is governed by a Board of Directors, which includes leadership from local city and county governments, special districts and Native Sovereign Nations. Vandervort also acknowledged and thanked District 5 Supervisor Jessica Pyska and former Supervisor Moke Simon for their leadership.

Highlighting recent achievements, Vandervort shared that in 2024, with increased funding and staffing, the RRA:

• Hosted 12 monthly meetings across Lake County.

• Launched a YouTube educational page and a website.

• Held two virtual town halls, including one focused on the Mediterranean Oak Borer.

To learn more about the RRA, visit the County of Lake “Boards & Commissions page” here.

To read the annual report slides, click here.

CLERC is also a key leader in mitigating wildfire impact and in serving as an environmental steward for Clear Lake’s ecosystem and Lake County. Will Evans, CLERC Co-founder and Executive Director, explained CLERC is “a nonprofit dedicated to studying and protecting Clear Lake, mitigating wildfire impacts and addressing Lake County’s environmental concerns, including the MOB.”

The MOB has become a growing concern for Lake County. District 5 Supervisor Jessica Pyska, who also chairs the RRA, explained that Dr. Curtis Ewing and Dr. Michael Jones, Forest Advisor at the University of California Cooperative Extension, first alerted the Lake County Board of Supervisors to the MOB’s presence in early 2023. Around the same time, Tracy Cline, CLERC’s Stewardship Director, observed signs of the beetle in Lakeport and South Lake County.

To address this emerging threat, CLERC biologist Julia Clickard presented the “Mediterranean Oak Borer Action Plan.” She explained “the MOB (Xyleborus monographus) is a tiny, reddish-brown beetle that is difficult to detect during inspections. Female MOBs, slightly larger than males and about the size of a pencil lead, can fly and are identifiable by raised bumps on their shell. Males, however, are smaller, flightless, and distinguished by a rhino-like horn.”

Clickard explained how the MOB’s life cycle damages oak trees:

“The MOB first enters a tree through its outer branches or areas where the bark is particularly thin. A single female beetle can initiate an infestation. They are less active in winter, hibernating from November to January, and re-emerge in spring when temperatures approach 80°F. Their peak season runs from March to May. The MOB takes 5 to 8 weeks to develop from egg to adult and can produce multiple generations per year.”

Clickard noted that it took years to understand how MOB became established in Lake County, emphasizing the importance of ongoing research and management efforts. Several oak species in Lake County are susceptible to MOB infestations, particularly the following:

• Tan Oak

• Live Oak

• Scrub Oak

• Valley Oak

• Blue Oak

• Oregon White Oak

• California Black Oak

• Of these, four are particularly common in the region.

To identify trees affected by the MOB, Clickard outlined the following key symptoms:

1. Black trellis patterns created by MOB bore into the xylem, which is the layer beneath the bark that is responsible for transporting water and nutrients. The beetle creates a network of interconnected tunnels, which turn black due to a fungus cultivated by female MOBs.

2. Tiny circular entry holes serve as MOB’s entry points are small and perfectly round, unlike other beetles that create D-shaped holes.

3. Pale boring dust often accumulates around entry holes, at the base of trees, or along limbs. Instead of frass, MOB produces this fine, pale dust as it tunnels through the xylem.

4. Branch dieback is one of the most visible signs of infestation, starting at the tips of branches and progressing downward.

These symptoms can easily be confused with water stress, climate change, high winds or other pests and diseases. However, Clickard emphasized the distinctive black trellis patterns and pale boring dust are key indicators of an MOB infestation.

Once inside the tree, the beetles burrow toward the trunk, gradually cutting off the tree's water supply. Female MOBs also introduce fungal pathogens from the Raffaelea and Fusarium genera, which can spread to other trees. “All ambrosia beetles, including MOB, have fungal associations,” Clickard stressed. “Some of these fungi are pathogenic and can speed up tree decline and mortality.”

Clickard shared several ways that Lake County residents can effectively help manage MOB infestations:

• Provide additional watering during summer to help trees stressed by drought.

• Thin tree stands to reduce competition, allowing each tree better access to resources.

• Prune trees carefully, cutting back to the node to prevent the beetle from spreading to the trunk.

• Properly dispose of infested materials by chipping, burning or masticating them on-site. Avoid moving these materials to prevent spreading the infestation.

• To further contain the spread, either burn infested materials or cover them with a tarp for six weeks in the winter or six months in the summer.

After extensive research, Clickard also updated ineffective methods. Burying wood after chipping is not recommended; however, if it is absolutely necessary and if it is the only option, burying chips at least five feet deep prevents beetles from escaping. Solarization is also no longer recommended, as it has proven ineffective.

Clickard emphasized that the most important step residents can take is to report any unusual behavior in oak trees on the CLERC website. Early detection is crucial, and CLERC focuses on community involvement at the core. Residents must learn to identify signs of infestation and CLERC provides educational resources on its website, including a map showing the intensity of MOB in various areas.

The CLERC survey is another valuable tool that allows the community to share information, which will be passed along to local and state agencies. As CLERC expands its network, the ultimate goal is to prevent the further spread of MOB. Clickard stressed, “Our aim is to gather data to secure a grant for management, similar to Oregon’s mobile burn unit or other methods.”

To learn more about CLERC and the “Mediterranean Oak Borer Monitoring Project” page, click here.

To read the “Mediterranean Oak Borer Action Plan,” click here.

To see current MOB distribution in CA, click here.