Although the fungus had been known in North America almost since its first discovery, for decades it was not considered to cause disease in its native range, and was largely ignored there until an outbreak occurred in the 1980s and 1990s.

After maturing for approximately nine months, the fungus produces pseudothecia which emerge from the stomata of the needle, dispersing new spores the following spring.

It produces small, spherical black fruiting bodies (pseudothecia) which obstruct the needle’s stomatal openings.

In some heavily infected stands of trees, the only needles remaining are those of the current year, in which the disease has not yet had time to fully develop.

Due to the reduced photosynthesis caused by needle loss, the tree experiences a diminished rate of growth by 52% or more.