DNA analysis of larvae from a tree in Pine Cove confirmed the presence of Goldspotted oak borer. CAL FIRE Forester Gregg Bratcher made the announcement at the April 24 Mountain Area Safety Taskforce meeting. Confirmation of Goldspotted oak borer in the tree on Pine Needles Lane brings the total of confirmed Idyllwild area infested trees to 11, according to Bratcher. “We’re seeing new GSOB trees at the rate of about one per week and that’s in the winter,” he noted.
Kevin Turner, University of California Riverside GSOB project coordinator, said they will ask the state forestry board to add Idyllwild as an additional GSOB Zone of Infestation. Last fall, the board established parts of San Diego County as a Zone of Infestation.
Goldspotted oak borer is thought to have been in San Diego County for at least 10 years, during which time it has caused widespread oak die off. One of the stated purposes of a zone of infestation is to “recognize GSOB as a threat to California’s forest and woodland resources and exhibit leadership in the effort to combat GSOB while providing the public with important information.”
Analyses of cross sections of Goldspotted oak borer infested trees removed in Idyllwild indicate the beetle has been present here for at least three years. In displaying a cross section of a tree recently removed from the western section of Marion View Drive, Turner said ring analysis seems to confirm that same time period. It would probably take five to seven more years before the broad devastation seen in San Diego County is clearly visible here, according to Forest Service entomologist Tom Coleman.
Confirmation of GSOB in Pine Cove expands the known micro zones of Hill infestation. Previously, oak borer infested trees were identified in four areas —along Highway 243 in the center of Idyllwild, near Town Hall, on Marion View near the American Legion Post 800, and on west Marion View nearer Idyllwild Arts. Although not contiguous, these zones were closer together than the new discovery in Pine Cove, which indicates wider area infestation than previously known.
Costs to remove and funding sources
The costs of taking down infested oaks average between $1,300 and $1,700, according to Bratcher. He said that if CAL FIRE grants are used to remove an infested tree, then no firewood from the tree can remain or be retained by the landowner. “That is the current line, we’re not leaving any firewood behind,” Bratcher said.
He advised the taskforce that current CAL FIRE funding for removing Goldspotted oak borer infested trees ends Sept. 30. “We’ve applied for an extension of the grant but if it is not approved our role would be limited to education only and cost of removal would fall on the landowner.”
Southern California Edison representative Dave Simmons has said that Edison would remove infested trees that threaten Edison lines at no cost to landowners.
Coleman advised the group that the Goldspotted oak borer’s flight season begins in May and still greater area-wide infestation is likely. Coleman said he had brought traps to track beetle migration during flight season which runs through July.
Efficacy of using topical sprays against GSOB
In response to an audience question about the utility of topical sprays, Coleman said all research at this point has been lab based and not field tested to any level of certainty. He said it is a five- to 10-year project to adequately field test efficacy of insecticides on Goldspotted oak borer infested trees.
“It is not easy to save a tree with insecticides,” Coleman said. A landowner could choose to spray a high value oak with chemicals that have shown some efficacy in laboratory tests or against other woodborers in other areas. But Coleman cautioned, that in his opinion, at this point sprays are better as preventive measures to be used on healthier trees than as curative actions on significantly infested ones. He recommended anyone with questions about treatment options should consult www.gsob.org, “Pest Notes,” for the latest information currently available. Costs of herbicidal spraying treatments are the responsibility of landowners, Bratcher said.
From “Pest Notes,” dated January 2013, is the following regarding chemical controls: “Although research testing various insecticides for GSOB management is underway, results are too preliminary to provide precise guidelines for this newly arrived species. … Trees with moderate to severe injury are likely to be difficult if not impossible to save with current management tools. Severely infested trees should be removed rather than sprayed and wood from these trees properly managed to prevent GSOB spread.”
Bratcher outlined the current property inspection process, usually initiated by a landowner calling the GSOB hotline, (951) 659-8328. Once Fire Safe Council teams make a preliminary Goldspotted oak borer finding, CAL FIRE does a second inspection, and then Forest Service and UCR scientists and staff perform a third to confirm the oak borer.