Deadly oak tree disease confirmed in Angels Camp
Live Oaks in Greenhorn Creek are infected with foamy bark canker.Photo by Paul Cooper

A beetle-transmitted fungus that has been killing oaks in coastal areas of California for several years now appears to have moved inland and was recently confirmed in oaks in Calaveras County.

Foothill Sierra Pest Control announced that on Oct. 18, University of California Farm Adviser Scott Oneto reported that samples Oneto took on Sept. 22 from infected trees in the Greenhorn Creek neighborhood were confirmed as foamy bark canker transmitted by western oak bark beetles.

Foothill Sierra owner Jim Tassano said that Oneto’s test confirmed an initial diagnosis made by Greta Shutler of the Tuolumne County Agricultural Department.

“We don’t know the source of the infestation,” said Foothill Sierra owner Jim Tassano, who is a biologist. “We are still researching.”

The disease, predominantly found in coast live oaks, was discovered in 2012 in El Dorado County infecting interior live oaks. The disease had not previously been discovered in Calaveras County.

The western oak bark beetle is a small beetle that burrows through bark, excavating shallow tunnels under the bark. The female beetles lay eggs in the tunnels and the developing larvae tunnel close to the surface.

The beetles often attack trees weakened by drought, disease, injuries and other stressors. But tree professionals say the beetle can also burrow in freshly cut oak firewood.

When the infection is at an advanced stage, the oak trees die.

“Thousands of trees have died from this. The trees will show a lot of decline and can get weaker and weaker,” said Tassano. “The disease robs it of its vigor and ultimately kills it.”

What causes the actual infection is the fungus the beetle carries, a species known as Geosmithia pallida.

Symptoms on the trunk and primary branches include discoloration and seepage from entry holes. A reddish sap may also be seen seeping from the entry holes followed by a prolific foamy liquid which can create a foamy trail up to two feet long down the trunk.

Currently, Foothill Sierra is treating the infected trees with an injected insecticide and fungicide. “We are trying to exterminate the disease,” said Tassano. “The objective is to stop it before it gets further.”

Tassano said he knows of no published research on the treatment of foamy bark canker. He hopes to develop treatment that could also be used in other areas affected by the disease.

Tassano will be reaching out to the residents of Greenhorn Creek with information as he has it as well as to report on the success or failure of his treatment plan.