Blue Stain Fungus is caused by the pathogen Grosmannia clavigera, carried by the mountain pine beetle. It infects pine trees when the adult beetle begins digging galleries to lay its eggs. The fungus chokes off the water-carrying vessels of the tree, killing it rapidly between one season and the next.

Plants Affected

  • Mostly pine trees, since these are the main target of mountain pine beetle.
  • Rarely, the beetle may experience host confusion and attack spruce trees. There is evidence that the fungus may colonize these spruce trees, but not to the extent of pine trees.


There is no chemical control for blue stain fungus available at this time. The only way to prevent it from infecting your pine tree is to prevent its vector, the mountain pine beetle, from reaching the tree.

  • Patch all mature pine trees with verbenone patches (available at local garden centres) before the end of June each year. This patch emits a hormone that discourages mountain pine beetle from attacking the tree. It will not work under mass attack conditions but does provide protection under most circumstances.
  • Examine your pine trees for beetle tunneling activity throughout July to October. Look for pitch tubes and holes in the bark, as well as sawdust accumulation at the base of the tree. Mild attacks of 1-10 beetles may be dug out if caught early enough. Contact Parks Operations at if you suspect your pine tree is being attacked by mountain pine beetle to discuss control or removal options.
  • Remove dead pine trees and burn, chip or bury the wood before the end of June to prevent beetle emergence and spread.
Fatal Blue Stain Fungal Infection
Pine Tree Killed by Blue Stain Fungus