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White pine blister rust
Cronartium ribicola
Synonyms
 
  • None

Plant hosts
 
White pine blister rust has a very complicated life cycle. Two different plant hosts are needed to complete the pathogen's life cycle.  All members of the genus Pinus (pine) that have 5-needles per bundle and all members of the alternate host in the genus Ribes (gooseberry and currant) are affected.
 
 
 

Symptoms
 
The first symptom is a small yellow or red spot on infected needles in the spring that can be overlooked. By fall, the fungus will grow into the bark at the base of these needles and the branch will appear swollen.  Dark lesions develop in this area and continue to develop into the characteristic diamond-shaped cankers. A distinct orange color appears at the margin of the canker and there may be abundant pitch flow from the canker.  Old cankers are rough and elongate structures that girdle trunks and branches, causing dieback or "flagging". From afar, infected trees have branches that look chlorotic, stunted, or dead.
 
Image of infected needles

Transmission
 
In the nursery industry, white pine blister rust is dispersed by the movement of infected planting stock.
In nature, the pathogen in the form of different spores, called basidiospores and aeciospores, are dispersed by the wind.

Geographic distribution
 
White pine blister rust is most severe in areas with extended cool, moist conditions during late summer and fall.  The pathogen has been reported in Asia, Europe, and North America.

Applicable regulations
 
There is no quarantine of white pine blister rust in Oregon, however, some other states and countries have regulations on the planting and movement of Ribes and susceptible Pinus species.
 
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