Sustain Our Nation's Forests and Grasslands

Preempting the pathogen

Rocky Mountain Bristlecone Pine (Pinus aristata) tree in Bristlecone Park, Colorado
Rocky Mountain Bristlecone Pine (Pinus aristata) tree in Bristlecone Park, Colorado. Photo courtesy of Jonathan D. Coop, Western State Colorado University

White pine blister rust is a devastating disease caused by a fungal pathogen that has been spreading through western forests since 1910. Native to Asia, it arrived in western North America in a shipment of seedlings, causing widespread mortality in a group that includes some of the oldest and highest-elevation pines in the United States—the five-needle pines. Threatened species include whitebark pine, limber pine and the bristlecone pine species.

While we cannot contain the disease, researchers with the Rocky Mountain Research Station and collaborators, led by research plant ecophysiologist Dr. Anna Schoettle, are developing proactive strategies that integrate conservation, ecology and genetics to prepare ecosystems for invasion of the pathogen. Hope for slowing the progress of the disease comes in the form of genetic resistance. As described in the latest RMRS Science You Can Use Bulletin, resistance, either partial or full, exists in a small percentage of individuals in each species susceptible to the rust. The research team is identifying how common this resistance is and where resistance is located on the landscape. They integrate this information with ecological research on population dynamics, climate interactions, and conservation activities to develop management strategies, such as planting resistant seedlings or creating regeneration opportunities near resistant trees.

Managers with the Forest Service, National Parks, including Rocky Mountain National Park, and Canadian land management agencies are putting this proactive approach into practice.

The pathogen was detected in Colorado in 1998 and will likely travel through the southern Rockies. Spores carried by the wind spread the rust. The spores germinate on the surface of pine needles, entering through the tiny openings in the needles (stomata), growing into the twig, infecting the branches and causing swelling and cankers to form. If the fungus reaches the main stem, it can prevent nutrients from reaching the branches and eventually kill the tree.

White pine blister rust canker on a limber pine branch
White pine blister rust canker on a limber pine branch. Forest Service photo by Anna W. Schoettle