Detecting Infestation

Are Mountain Pine Beetles Infesting My Trees?


During outbreak conditions, all trees - weakened and healthy - are susceptible. The summer that a tree is attacked it will appear green and healthy. The first signs of the attack will be noticeable by late summer.

  • Pitch Tubes, or small (1 to 2 inch) masses of resin will be present on the trunk.
  • There will also be red boring dust in bark crevices and on the ground and the tree.  This boring dust will have a size and consistency ranging from flour-like to sugar-like
  • Sometimes if the tree is very health and the attacks are limited, the tree can "pitchout" the beetles.  These trees can be identified by larger pitch tubes with the adult beetle often stuck in the resin.
  • If the attacks were successful, with C-shaped grubs can be readily found beneath the bark by August or September

At this point the trees are usually beyond recovery. The following spring the needles on these attacked trees will turn a yellow to a bright red. The wood will show blue-staining by the fungus Ceratocystis montia. After the adult beetles emerge, the dead trees turn a dull red, becoming gray the following year. There are other insects and disorders that can be confused with some of the symptoms and signs of mountain pine beetle colonization.