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Identifying Tree Mortality - Signs of Bark Beetle Infestation

Do you have a tree mortality issue on your property? Read these signs to see if you have been impacted by the bark beetle and need to take action.

Illustration of Bark Beetle Size                         Photo of a Bark Beetle

The Bark!

  • When trees are attacked by bark beetles, they defend themselves by releasing pitch. Evidence of a tree releasing pitch will be a small white or reddish-brown “pitch tube” which forms on the outside of the tree (these pitch tubes may also resemble by blobs of sap-like substance).

  • A white pitch tube indicates that the beetle was successfully repelled by the tree, while a reddish-brown pitch tubes indicates that the beetle was most likely successful in attacking the tree.

            Illustration of Brown Pitch Tube                          Photo of White Pitch

  • The pitch will be accompanied by a sawdust-like substance, called frass, created by bark beetles and their larvae as the work their way through the bark and the tree.
  • Frass will accumulate within tree crevices and may fall to the ground, which will resemble very fine reddish-brown coffee grounds.

Frase photo like sawdust around base of infected tree                         Photo of closeup of frase

  • Bark flaking or holes in the bark, which are normally caused by woodpeckers, are also a good indicator that bark beetles are present within a tree.

A closeup of bark flaking on infected tree                         Another  photo of bark flaking

  • Removing bark sections will reveal holes created by bark beetles, as well as dead or degraded inner bark

Photo of inner bark with bark beetle holes                         Another bark whole photo comparing to tip of a pen.

Leaves or Needles?

  • The needles on conifer trees, like pines, begin to turn a reddish-brown color. Often the change begins at the top of the trees and moves down.
  • Some trees may slowly fade in color from green to brown.
  • Some trees may die within a few weeks of infestation, but may not show yellow-green, fading or red foliage for several months. Other types of trees may survive years before dying; by the time a tree appears dead, it cannot be saves.

Photo of an infested forest                    Mountains show an area of infected trees

Determining if a tree is dying can be considerably more difficult than determining if it is dead. While the foliage of a dead tree will have changed color uniformly throughout the crown, the foliage of a dying tree will be green in the whole or in part. The California Forest Practice Rules defines a dying tree as one that meets one or more of the following criteria:

  • At least fifty percent of the foliage bearing crown has notably changed uniformly in color over that part of the crown, which indicates that the crown is recently dead.

These tools can be very helpful in identifying a dead tree and are pretty straight forward, but in some cases determining if a tree is dying from bark beetle may require special determination by a qualified evaluator. Different tree species are attacked by different beetles, more than one species of beetle will attack an individual tree, and the different beetle species vary in their ability to kill trees. Similarly, the indicators of beetle attack will differ based on beetle and tree species.