The fungus usually infects trees that are weakened by environmental stress, such as drought and freezing shock. Infection usually does not begin until trees are at least 10-15 years old.
The fungus generally enters through wounds. The infection usually starts on the lower branches and spreads upwards as spores of the fungus are dispersed by rain-splash. Needles on infected branches first turn purple and then brown and drop, leaving the infected branches bare. Cankered branches are usually covered with white resin.