Pathology Sirococcus Shoot Blight of Spruce Sirococcus shoot blight of spruce was diagnosed recently in the Plant Disease Clinic. The disease is caused by the fungus Sirococcus conigenus and predominantly affects the current year's growth on pine, spruce, and hemlock. Young seedlings may be killed by the disease, but damage to large trees mainly is confined to lower branches and has slight effect on plant health. The fungus infects needle bases in late spring and early summer. Small purple lesions are formed and a drop of resin is exuded at the point of infection.
Infected needles become chlorotic, die, turn reddish-brown, and are shed.
Infection may spread into the stem, causing a canker. If infection occurs in the region of shoot elongation, growth in the infected tissue is stopped, causing hook-shaped tip growth. The fungus overwinters in killed shoots and cone scales. Small, black fruiting bodies form on killed tissue in late summer, early fall, or in the spring following infection. Spores are dispersed from infected tissue to susceptible hosts by rain splash.