White Pine Blister Rust

Cronartium ribicola

Invader Images

    • Flagging - browning of pine needles
    • Spore stage of white pine blister rust on stem of sapling
    • Flagging in top branches of Eastern white pine
    • Spore stage on stem of young tree
    • A white pine blister rust canker on a young white pine
    • Currant leaf showing signs of white pine blister rust
    • Cushions under the bark in spring

Identification

White pine blister rust (WPBR) is caused by the fungus Cronartium ribicola and affects white pine trees. Symptoms vary with different stages of spore and canker development. The fungus has five spore forms in its life cycle: two (pycniospores and aeciospores) occur on pine, and the others (urediospores, teliospores, and basidiospores) occur on the alternate hosts, currant and gooseberry (Ribes) bushes. The fungus cannot spread from pine to pine.

signs and symptoms

  • "Flagging" or browning of pine needles
  • For initial infection, look for patches of brownish bark bordered by a yellow discoloration
  • Year-round look for cankers bordered by a yellowish discoloration at the canker margin
  • Breaks in the bark cankers and a resulting flow of resin
  • Signs of rodents feeding on the cankers
  • Orange-yellow blisters
  • Orange spores on the underside of Ribes leaves in summer
  • Brown hair-like projections on the underside of Ribes leaves in late summer

See image slideshow above for signs and symptoms.

Biology

Origin

White pine blister rust is native to Asia. It was brought to North America around 1900, and since then has spread throughout the range of white pine.

Life Cycle

White pine blister rust’s life cycle requires two phases on two different hosts: white pines and a Ribes species (often currant and gooseberries). The spores of the fungus develop on the Ribes host and then spread to the white pines. The fungus may defoliate theRibes host but seldom causes serious harm. However, it can cause mortality in white pine trees. Visit High Elevation White Pines website or American Phytopathological Society website for an in-depth explanation of this fungus’s complex lifecycle.

ecological threat

In Vermont, white pines are a valuable natural and economic resource. Trees fill an important ecological niche, providing food and habitat for wildlife such as porcupine, squirrels, and beaver. Its wood is highly valued for timber, wood working, and Christmas trees. Ribes species produce edible berries that are consumed by both wildlife and humans.

Management Options

  • Promote awareness of white pine blister rust among gardeners and consumers. Growing interest in the health and culinary benefits of currants have increased the risk to pine trees. The white pine blister rust fungus has shown its ability to mutate and infect Ribes cultivars once thought to be resistant.
  • Suspect white pine blister rust when a single branch dies suddenly. If caught early, individual trees can be saved by pruning the dead branch at the mainstem.
  • In forest situations, white pine blister rust causes only widely scattered mortality of mature trees. Disease incidence on young trees can be reduced by regenerating pine under an established overstory, or preventive pruning of lower branches. For more information consult How to Manage Eastern White Pine to Minimize Damage from Blister Rust and White Pine Weevil.

Vermont Distribution

White pine blister rust has spread throughout Vermont.

White pine blister rust North America distribution map

Citations

Photo Credit

Andrej Kunca, National Forest Centre - Slovakia, Bugwood.org

Joseph OBrien, USDA ForestService, Bugwood.org

Mike Schomaker, Colorado State Forest Service, Bugwood.org

Steven Katovich, USDA ForestService, Bugwood.org

information credit

HortTechnology

Plant Management Network

The American Phytopathological Society

USDA Forest Service