Environment & Science

'Foamy Bark Canker' fungus killing California oak trees up and down coast

A fungus that causes foamy bark canker disease has been found in California coastal live oak trees in six counties. The cankers seen here can grow to be much bigger, producing a large amount of foam that seeps several feet down the tree.
A fungus that causes foamy bark canker disease has been found in California coastal live oak trees in six counties. The cankers seen here can grow to be much bigger, producing a large amount of foam that seeps several feet down the tree.

Listen to story

01:00
Download this story 0.0MB

A fungus never before seen in California oak trees is threatening the state's coastal live oaks from Orange County to Monterey.

Researchers at UC Riverside issued an alert after they found a high incidence of the fungus in six counties including Orange, Los Angeles, Riverside, Ventura, Santa Barbara and Monterey.

The fungus causes a condition known as "foamy bark canker disease," which leaves large weeping cankers in the bark of affected trees, with foam seeping several feet down the trunk. The cankers may be covered in a cinnamon colored gum with creamy colored foam.

Reports of infestation by the fungus, Geosmithia pallida, began just six months ago, according to UC Riverside plant pathologist Akif Eskalen. It's carried by a beetle that is native to the state, but has never previously been found to carry the disease.

The Western Oak Bark Beetle bores into oak trees to lay its eggs and deposits the fungus inside. The fungus grows to block the circulation of water and nutrients, killing branches and eventually the whole tree.

Researchers have asked the public to contact local agriculture officials if they notice any symptoms of the fungus on trees in the area.