White Pine Blister Rust
Cronartium ribicola
Overview
A devastating rust disease of five-needled (white) pines requiring Ribes (currants/gooseberries) as an alternate host. Has severely impacted western white pine and whitebark pine populations.
Symptoms
On pines: orange-yellow blisters on branches and trunk that rupture to release white spores. Cankers girdle branches causing flagging. Trunk cankers lead to top-kill and death. On Ribes: yellow-orange pustules on leaf undersides.
Environmental Conditions
Humid
Prevention
Plant rust-resistant white pine selections. Remove Ribes plants within 1,000 feet of pines. Prune lower branches to reduce infection. Avoid planting white pines near Ribes.
Management
Prune infected branches at least 4 inches below canker margin. Remove Ribes alternate hosts. Plant resistant selections. No effective fungicide for forest settings. Pruning trunk cankers is rarely successful.