Stalactiform blister rust
Damage, symptoms and biology
Mortality may occur as a result of girdling of small diameter stems, and as such can act as a natural thinning agent in young stands. In older trees stem defects occur, reducing wood quality and predisposing trees to damage from wind and heavy snow. Atropellis piniphila is often associated with stalactiform blister rust cankers.
Cronartium coleosporioides can be distinguished from C. comandrae by its more elongate cankers, and more precisely by its ellipsoid aeciospores (cf. pear-shaped aeciospores of C. comandrae). Differentiating between C. coleosporioides and C. comptoniae is more difficult. The longitudinal hypertrophied ridges produced by sweet fern blister rust are not present on stems infected by stalactiform blister rust. In addition, the aecial filaments of C. comptoniae are continuous, whereas those of C. coleosporioides are pendant. Identifying the presence of the alternate hosts will also help distinguish between these two rusts. Non-sporulating cankers may also be confused with those caused by Atropellis piniphila.