Stem Decays and Stains
FIELD GUIDE TO INSECTS AND DISEASES OF ARIZONA AND NEW MEXICO FORESTS

Blue Stain Fungi
Ophiostoma spp.
Ceratocystis
spp.

Hosts:  Conifers

Figure 204. Blue stain fungi invade the sapwood.Symptoms/Signs:  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.

References:  92, 100