Distribution and Disease Cycle
Current year's shoots are infected when spores are dispersed in May and June from galls on branches and stems. Galls form in the summer following the year of infection, with sporulation not occurring until the subsequent spring. Galls can weaken stems, increasing the incidence of wind breakage. Extensive gall formation can cause tree stunting or mortality.
Symptoms and signs
Infection by western gall rust results in round or pear-shaped galls on branches or stems of susceptible pine hosts. In spring, the gall surface ruptures, releasing bright orange spores. Cankers sometimes form on main stems near galls; in some cases infection can result in production of witches'-brooms.