The Big Sandy Mountaineer -

Green Acres


May 8, 2019

Cytospora Canker

The fungal disease Cytospora canker is common in Montana and is most damaging on Colorado and Norway spruces. The first indications of Cytospora canker are dying lower branches with bluish-white-colored resin flowing from cankered areas. Upper branches die in subsequent years. Infected inner bark and the cambium tissue directly below the bark are brown, whereas healthy tissues are light-colored. Removal of outer bark slivers just beyond the resin soaking often exposes black pinhead-sized depressions (spore-producing fungal bodies).

Cytospora invades trees through wounds. Splashing rain, wind, insects, birds, rodents, and man spread disease spores to new branches or other spruces. Older trees weakened from drought and hail injury are most susceptible. Other environmental stresses such as insect or mechanical injury also favor Cytospora.

Remove and destroy infected branches. If infected branches are not removed, birds will transfer the fungus to other branches. The best time to prune is in late winter before spores are released in the spring; however, it is acceptable to prune dead branches at any time of year. If the weather is dry. Prune 4 to 6 inches ahead of the canker, cutting back to the nearest living lateral branch or to the trunk. Disinfect tools between cuts to avoid spreading the disease. Fungicides are not effective against Cytospora.

White Pine Weevil and the

Western Pine Shoot Borer

The white pine weevil and pine shoot borer cause leader shoots of spruce to become crooked and die, forming a characteristic “shepherd’s crook.” Larvae cause most of the damage by boring out the center of the terminal (top) leader. Consequently, spruce trees become multiple-stemmed and bushy. Young trees can be killed.

Shoot borer larvae have legs, whereas pine weevil larvae are legless. Shoot borer adults are gray moths (3/4 inches long) with copper colored bands on the wings. Adult weevils are mottled brown and white, have a long curved snout, and are about 1/4

to 3/8 inches long. Adults emerge in late summer and overwinter in the ground. In the spring, adults of both species lay eggs on the bark of the terminal leader. Larvae emerge in 7 to 10 days and tunnel downward between the bark and wood of shoots.

Pruning and destroying infected shoots as soon as they are noticed is the best control for both pests. Spring control of adults may be accomplished by spraying terminal leaders with a systemic insecticide, although spraying must be timed with adult weevil or moth activity.

Information for this article comes from Montguide 199809 (Growing Spruce Trees in Montana). The publication contains extensive information about spruce trees best adapted to Montana’s climate. It includes sections on types of spruce; advice on obtaining spruce cultivars; recommended techniques for planting, watering, fertilizing, pruning; and information about diseases and insect problems. Copies are available from the Chouteau County Extension Office. We are located in the green building next to the courthouse.

Montana State University, U.S. Department of Agriculture and Montana Counties Cooperating. MSU Extension is an equal opportunity/affirmative action provider of educational outreach.


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