White Pine Blister Rust (Cronartium ribicola)

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Hosts: Western white pine, whitebark pine

Quick ID:

Branch flagging
Swellings and blisters on branches; also on trunk of small trees
Diamond-shaped cankers on trunks
Cankers with greenish-yellow to orange margins
Pustules of orange spores on cankers and branch swellings
Resin flow from branch and trunk on advanced infections
Field Identification

Tree: This disease does not affect species outside of the white (5-needle) pine group (similar symptoms on lodgepole or ponderosa pine may be caused by western gall rust). The foliage may have red or yellow needle spots. On the branches, spindle-shaped swellings or cankers with small cup-like indentations are frequent. Often infections kill the branch, resulting in bright red "flags" in the crown. On the trunk, a diamond-shaped canker with dead roughened bark and greenish-yellow to orange margins develops.

Natural Resource Sciences, Cooperative Extension, PO Box 646410, Washington State University, Pullman, WA 99164-6410 USA