White pine blister rust has a complicated life cycle. Only spores from alternate hosts such as currants and gooseberries can infect white pine; spores from white pines cannot infect other white pines.
A flagging branch (needles on a branch that turn yellow at first and eventually reddish-orange) is the initial symptom of the disease. The branch dies because of a canker (dead zone of bark) that forms from the infection.
Cankers girdle branches. On smaller branches cankers are swollen and have rough bark, but on larger branches and the main stem they appear as sunken zones. Branches and main stems exude resin that hardens and forms a substance resembling white paint. The most obvious sign of blister rust is its dusty, yellow-orange fungal fruiting structures that form on the margins of cankers in spring.
A canker on the main stem results in death above the canker (top-kill on larger pines) or death of the entire tree.
Flagging branch on young white pine.
White pine blister rust fruiting structures.