Disease

White pine blister rust

Cronartium ribicola

A rust fungus of five-needle pines that also needs currants or gooseberries nearby to complete its life cycle. It forms swollen cankers on branches and the trunk, and a canker that reaches the trunk kills the top or the whole tree.

Signs

• One branch with all its needles turning yellow, then rusty red.
• A swollen, rough canker on the branch or trunk, oozing sticky clear-to-white sap.
• White to yellow blisters at the canker edge in spring that burst with orange powder.

What favors it

Currants and gooseberries nearby, especially within 200 feet, cool, moist sites, and low branches within 10 feet of the ground.

Prevention

• Plant rust-resistant white pine selections, and only rust-resistant currants and gooseberries near pines.
• Prune the lower third of white pines every few years until there are 9 feet of clear trunk, never more than half the live crown; most lethal infections start within 10 feet of the ground.

Crops it shows up on

Evergreens & conifers (pine, spruce, juniper).

Often confused with

Sources

• White pine blister rustUniversity of Minnesota Extension
• White Pine Blister RustUniversity of Wisconsin-Madison Plant Disease Diagnostics Clinic
• White pine blister rust managementMinnesota Department of Natural Resources

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