White pine blister rust was introduced from Europe and Asia. The fungus affects all five-needle pines, including western white pine found at low- and mid-elevations in the Swan Valley and whitebark pine, which generally grows above 6,000 feet.
The fungus forms cankers on the branches and tree trunk. Cankers on the trunk will affect the cambium layer beneath the bark and eventually girdle the tree. It may take several years for blister rust alone to kill a tree. Yet, when weakened by the fungus, the trees are susceptible to mountain pine beetle and other maladies that can be deadly within months.
Appearance
The cankers may display one or more of these symptoms: a rusty discoloration on the branches or trunk, pitch oozing from the infected area, orange/yellow powdery spore blisters, and cracked or sunken bark above the dead cambium. Often red needle flagging on a branch is the first symptom noticed, indicating the canker has girdled and killed the leading end of the branch. The canker will move toward the trunk, where it will eventually kill the tree top.
Management
Western white pine has high value for timber production. And the seeds of the whitebark pine are an important food source for bears, Clark's nutcrackers and pine squirrels. Efforts to propagate trees resistant to blister rust may prove effective for re-establishing western white pine and whitebark pine stands. Resistant trees can be ordered in the fall for spring planting from the DNRC Montana Conservation Seedling Nursery,
www.dnrc.mt.gov/forestry/Nursery/.
For more information visit
www.fs.fed.us/r1-r4/spf/fhp/mgt_guide/index.htm. |
