Cronarlium ribicola Fisch.

From: Field Guide to Diseases and Insect Pests of Idaho and Montana Forests, USDA Forest Service Northern Region, Publication Number R1-89-54

Hosts. – Five-needied pines including western white pine, limber pine, and whitebark pine. Ribes spp. (currants and gooseberries) are alternate hosts.

Distribution. – The pathogen was introduced from Europe and Asia in the early 1930's. It has since spread throughout most of the range of the pine hosts.

Damage. – The fungus causes branch and stem cankers that eventually cause top kill or death of most infected trees. Generally, the larger the tree is at the time it becomes infected, the longer it survives after infection.

Identification. – The earliest symptom usually detectable is discoloration (fig. 16) and pitch flow from a patch on an infected twig or branch. The needles on the branch die and droop as the fungus girdles the branch. The bark is sunken or cracked above the dead cambium. The fungus moves up the branch and into the stem. Stem cankers usually have abundant resin flow on the outer bark (fig. 17). The outer margin of the canker appears as a discolored area surrounding the dead bark. Infected trees may appear vigorous until shortly before death. Some trees may have squirrel or porcupine chewing at the canker margins. In spring, the fungus often sporulates at the canker margins producing yellow to orange, powdery tongues of spores in bark cracks (figs. 18, 19).

Similar damages. – Armillaria root rot causes resin flow at the base of trees similar to that which results from basal stem cankers of white pine blister rust. If Armillaria is present, white, fan-shaped felts of inycelium will be present in the carnbium beneath the resinous bark. Squirrels or porcupine feeding may be present without blister rust cankers.

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References.

Anonymous. 1982. For. Insect & disease identification and management. USDA For. Serv., Northern Region; Idaho Dept. of Lands, Insect and Disease Control; Montana Dept. of State Lands, Division of Forestry. 192 p.

Bega, R.V. 1978. Diseases of Pacific Coast conifers. USDA For. Serv. Ag. Hndbk. No. 521, 206 p.

Boyce, J.S. 1961. Forest Pathology. McGraw-Hill Book CO., New York, NY. 572 p.

Hepting, G.E. 1971. Diseases of forest and shade trees of the United States. USDA For. Serv. Ag. Hndbk. No. 386, 658 p.

Ziller, W.G. 1974. The tree rusts of western Canada. Can. For. Serv., Publ. No.1329, Dept. of the Env., Victoria, B.C. 272 p.

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