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University of Illinois Extension

White Pine Blister Rust

Cronartium ribicola 

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.   

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.


Filed under plants: Evergreen Trees & Shrubs

Filed under problems: Fungal Disease

More information is available on Hort Answers.