What is blue stain fungus?

What it looks like

Cut across a beetle-killed pine and the outer wood, the sapwood, often shows wedge- or fan-shaped streaks from the bark inward. The color ranges from pale gray to a dark blue-black. The stain follows the paths the fungus took along the rays and cells of the wood.

The stain is a color change, not rot. Stained wood is generally as strong as unstained wood, which is why the fungus is a clue about how a tree died rather than a measure of whether the lumber or firewood is sound. Decay is a separate matter; see conks and cavities.

Why it matters in Northern Nevada

Dead and dying pines are a regular sight in the Sierra foothills, the Carson Range and around Tahoe, and bark beetles are part of the story in many of them. Blue stain shows up in a pine that has been dead for a while, so it can help confirm a cause after the needles have already turned. It also tells a homeowner the tree was not a victim of a single odd event: if one pine on a lot has died this way, neighboring pines under the same drought stress deserve a look.

Dead pines are also fuel. A tree that died of beetle attack and stands within the home zone of a house is a fire concern as well as a falling one. See removing dead pines after bark beetles.

What an arborist does about it

The arborist uses the stain as one piece of the diagnosis, along with pitch tubes, boring dust, the pattern of needle loss and the tree's species and setting. The decision that follows is not about the fungus. It is whether the tree is dead, whether it can fall on something, and whether to remove it or only prune. Battle Born does not treat trees; we identify the problem and handle the removal or pruning.

One practical point: the stain does not make a dead pine safer or less safe. Dead wood dries, becomes brittle and can fail, whatever its color, so the decision about a dead pine near a house turns on what it could hit.