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Oak Tree Beetle Threat

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Posted: Thursday, January 27, 2011 12:00 am

The message was loud and clear: If you're going to purchase oak firewood, make sure it was taken locally and is well seasoned.

The warning came from Tara Piraneo, the coordinator of the Early Warning System program at the University of Riverside Cooperative Extension, and Kevin Turner, a retired forester and fire division chief who is the head of the university's goldspotted oak borer (GSOB) program.

This beetle, which has invaded San Diego County, is slowly moving north. Piraneo and Turner expect it to eventually reach the San Bernardino Mountains. One of the ways it is spreading is through infested firewood from other areas, such as the San Diego area.

Piraneo and Turner were part of a sobering discussion at the Jan. 16 Inland Empire Fire Safe Alliance meeting at the San Bernardino National Forest headquarters in San Bernardino. This tiny beetle has the capability of stripping vast areas of coast live oak, canyon live oak and black oak trees of their leaves and then leaving them to die. Its destructive appetite can cause a 90 percent die-off of the trees in areas it invades.

Turner said he first heard about the beetles attacking oak trees in the Cleveland National Forest and, he said, the odds are good they will migrate to Riverside County. He said the infestation has the potential to spread throughout California's national forests and move into forests in Oregon.

The infestation will only affect oak trees. The first time the beetles were observed in California was in 2004 and they have been moving ever since. Foresters believe the first time they were spotted anywhere was in the late 1800s in Arizona and they believe they migrated from Northern Guatemala and Mexico, Turner said.

He explained that in San Diego County they have killed tens of thousands of oak trees in a 30-square mile area. So far, the infestation is still only in San Diego County but it is on the move. He added that their "elevation range" is large and they don't seem to be affected by altitude or the cold so they are able to attack trees in mountainous areas.

While the bark beetle infestation that was responsible for killing millions of pine trees in the San Bernardino and other national forests may have been due to California's years-long drought, the infestation by this new beetle is not just an effect of the drought.

Turner said that the beetles' flight pattern is usually from May to July so they are expecting the new "flight" to resume in just a few months. "If they have plenty of food, they usually stay within a five or six kilometer range. If they have plenty of food 'next door,' they probably won't have the incentive to fly great distances," he said. He added officials won't know how far up to expect them to go until they actually begin their "migration."

According to Turner, the beetles can completely ravage an area with an 85 percent oak tree die-off. In San Diego County statistics show that at least 22,000 trees have been killed with estimates as high as 50,000. The beetles do the most damage in the higher tree branches and leaves. They will completely strip a tree of its of leaves in five months, Piraneo. Because the leaves turn brown, the sustainability of wildlife that feeds on the leaves found mostly in the higher (or crown) branches is affected.

Signs that oak trees are infested with the goldspotted oak borer include extensive bark staining; a "D-shaped" exit hole from the tree; branch or twig injury; and entry holes that are red and cause red-colored damage to the bark. Once the beetles have left the tree, it may take up to nine years for the tree to actually die.

At this point there is no solution to the problem but management options are being studied, Turner and Piraneo said. While insecticides are being researched that will kill the beetles, a large-scale program can't begin until any chemical eradication program has proven to be successful.

Piraneo asked alliance members to help spread the word about the oak beetle infestation. "You become our eyes," she said, adding the public has always played an integral part in noticing changes in tree growth and problems in the national forest and reporting them. She encouraged attendees and the public to log on to www.gsob.org for information.

Alliance President Laura Dyberg said the Arrowhead Lake Association already has information on their website (www.ala-ca.org) warning residents and visitors not to bring any firewood from San Diego County up to the mountains.

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