Western oak bark beetles are a tiny beetle native to California that bore into oak trees to lay eggs. The beetles carry a fungus that results in unsightly cankers and cause serious damage to trees.

Small entry holes indicate the presence of the beetle. When bark near these holes is peeled away, death of tree tissue around the hole will be visible. As the disease advances, a cinnamon or reddish colored sap appears. This is followed by a creamy, foamy sap that oozes from the entry holes and down the bark. Depending on the level of beetle infestation, there may be hundreds of these holes on an infected tree’s trunk and branches.

Given that this disease is spread by beetles, simply keeping trees healthy is the best way to prevent infection. These beetles are attracted to stressed trees so maintaining vigor through fertilization plays a major role. Proper irrigation and mulch are also important.




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