*******61********** White Pine Blister Rust (Cronartium ribicola)-Hort Answers - University of Illinois Extension
University of Illinois Extension

University of Illinois Extension

Hort Answers

Fungal Disease

White Pine Blister Rust
Cronartium ribicola

Picture courtesy of Mich. Depart. of Ag.
Picture courtesy of Mich. Depart. of Ag.
 
Frequency
4 (1 = rare 5 = annual)
 
Severity
5 (1 = very little damage 5 = plants killed)
 
Hosts
The disease affects both Eastern and Western white pine for part of the disease cycle. Numerous species of the genus Ribes are involved in other parts of the disease cycle.

 
Plants Affected
 
Symptoms
On pine, symptoms include yellow dying needles that often drop early and cankers that usually girdle branches and and trunk. The cankers often cause death of branches and the tree. Cankers usually cause bleeding in infected areas. In spring yellowish orange blister develop in canker areas. Canker areas may be swollen or sunken and are rough and cracked looking. Lower branches are usually killed first.

 
Life Cycle

The pathogen can spread several hundred miles from pine to currants but only a few hundred yards from currants to pine. Infection of pines occurs through the stomates in the needles between midsummer and early fall when weather is wet. The fungus grows down the needle into the young branches. The fungus grows through the rays cells in the sapwood and between cells in the bark. The growing rust mycelium is what causes swelling in the bark. Disease spores are released one or more years after infection.

Infection of the ribes plants starts on the lower leaf surface. These infected leaves release more spores that reinfect the ribes plants. Lowering temperatures and shortening days result in the ribes releaseing spores that infect the nearby white pines.

 
Management

Eradicating Ribes plants has not worked to eliminate the disease but may help slow the disease spread. Pruning off the lower branches can help if done before rust symptoms on the branches get within six inches of the trunk. Pruned off branches can be left since the pathogen can not survive in dried out tissue. If symptoms develop within six inches of the trunk, removal of the tree is suggested to help reduce spread of disease.

Click here for more information about the history of this disease, or here for information about resistant and immune Ribes species and varieties.

 
Related Resources
Home, Yard & Garden Pest Guide
Illinois Commercial Landscape and Turfgrass Pest Management Handbook
U of IL - Distance Diagnosis through Digital Imaging
U of IL - Plant Clinic