Blue-green discoloration of sapwood (often in wedge shapes)
in recently killed trees. Blue stain fungi frequently originate
from bark beetle galleries.
Biology: Blue stain fungi are carried by
bark beetles and other wood inhabiting insects and are associated
with tree mortality. They are mostly blue-staining and primarily
from the genera Ophiostoma and Ceratocystis. The
spores germinate and produce a mycelium (thread-like mass) that
colonizes the phloem and sapwood, eventually blocking the water-conducting
columns of the tree. The formation of a wedge-shaped stain is due
to movement of hyphae along the rays from the outside of a log.
Effects: Stain fungi often hasten the death
of trees attacked by bark beetles. The stain may result in a reduction
in the value of timber or timber products by discoloring sapwood,
but does not affect wood strength.
Similar Insects and Diseases: Another group
of sapstaining fungi are wind disseminated, of various colors (blue,
brown, or gray) and are from the genera Aureobasidium and
Alternaria. Black stain fungi, which are closely related
to blue stain fungi, also block water-conducting columns. However,
black stain fungi spread to healthy trees by root-to-root contact.