Pruning Blister Rust Cankers to

1
Pruning Blister Rust Cankers to Preserve
High-Value Trees
Kelly Sullivan Burns1, Amanda Crump2, William
Jacobi2, and Brian Howell1 1USDA Forest Service,
Rocky Mountain Region, Forest Health Management,
2Colorado State University, Department of
Bioagricultural Sciences and Pest Management
Methods Sample trees were tagged and
mapped. Pre-treatment data was recorded for each
tree including DBH, maximum needle retention,
height, health status, crown class, live crown
ratio, and information on the amount and
distribution of cankers. Infected sample trees
were randomly assigned one of four treatments
prune to a set height, prune all cankers, prune
to set height and prune all cankers, and no
action. Uninfected sample trees were randomly
assigned one of two treatments no treatment or
prune to a set height. Trees with lethal
infections were not included in the study. Trees
were split into three DBH classes (lt 4, 4-8, gt
8). Treatments were replicated in blocks by
diameter class by randomly selecting 18 trees (3
replications of each treatment) within each
class. Post- treatment data collected
included number of cankers removed and
remaining number of people treating the tree
and treatment time.
Introduction White pine blister rust (WPBR) is
an exotic, invasive disease of five-needle pines.
The fungus causes cankers which usually kill the
stem above the canker, often leading to
mortality. In southern Wyoming and Colorado,
limber and bristlecone pine are especially
important because of their unique cultural and
ecological characteristics (Schoettle 2004).
Protecting and preserving high-value and
culturally significant trees in recreation areas
is a concern for land managers, however,
silvicultural strategies for rust management have
not been tested for these tree species.
Management techniques are available for
prolonging the life of other white pine species
(see Hagle 1989, Hunt 1988, Hunt 1998) and these
techniques may be effective and cost-efficient
for limber and bristlecone pines. The purpose of
this study was to evaluate the efficacy of
pruning and canker removal treatments in reducing
infections and decreasing mortality and to assess
several pruning treatments in terms of cost,
feasibility, and effectiveness.

• Preliminary Results
• Mosca Pass
• One hundred sixty-seven trees were included in
  the study (14 bristlecone and 153 limber pines).
  
• Twenty-nine percent of the bristlecone pines and
  69 percent of the limber pines were infected with
  WPBR.
• There was an average of 6 cankers per tree (range
  0-54).
• The average height of cankers from the ground was
  12.9 feet and the average distance of cankers to
  the main stem was 7.8 feet.
• We removed 207 cankers by pruning the entire
  branch, 14 by scribing, and 201 by removing a
  portion of the branch.
• The average time to rate trees was 12 minutes and
  the average time to treat trees was 11 minutes.
• This project was completed using 6-11 people per
  day for 2 weeks.

• Preliminary Results
• Vedauwoo
• We initiated a 100 percent survey of the CG in
  late June 2005 however, cankers were difficult to
  identify because aecia were no longer present.
  We tagged and surveyed 682 limber pines.
• 221 (32.6) trees were fatally infected.
• 135 (19.9) trees were uninfected.
• 321 (47.5) were infected but treatable.
• We treated 226 operational trees in August 2005.
• Data collection and treatment of 207 study trees
  will occur during the spring of 2006.
• Average treatment time was 8.5 minutes and a crew
  of 6-10 completed the work in one week.
• Future Plans

Study locations included the upper portion of the
Mosca Creek Trail, Great Sand Dunes National Park
and Preserve (Sangre de Cristo Mountains),
Colorado and Vedauwoo Campground, Laramie Ranger
District, Medicine Bow National Forest, Wyoming.
We scribed the bole when cankers were within 12
inches of the main stem. Scribing was done at
least 3 inches proximal to the visibly infected
area.
Non-lethal stem cankers were removed by pruning
the main stem 12-18 inches below the canker.
Aecia were visible and spores were being released
in mid May. By late June, cankers were difficult
to identify.
Distribution of WPBR in the Central Rocky
Mountains WPBR was discovered in northern
Colorado in 1998 (Johnson and Jacobi 2000).
These infections are the result of southward
spread from Wyoming where the disease has been
present since the 1950s. WPBR has been present
on limber pine on Pole Mountain for at least 25
years (Kearns 2005). The disease was identified
on limber and bristlecone pines in the GSDNPP in
2003 (Blodgett and Sullivan 2004). This was the
first time blister rust had been observed on
bristlecone pine in its native range and the
incidence of infection along Mosca Creek may be
as high as 75 (Blodgett and Burns, July 7, 2004
letter).
White pine blister rust was discovered on
bristlecone pine for the first time in its native
range in 2003 in the Great Sand Dunes National
Park and Preserve.
Acknowledgments We would like to thank Phyllis
and Ola Bovin, Jim Worrall, Brian Geils, Bob
Cain, Clint Kyhl, Paul Blackman, and the many
Laramie Ranger District, GSDNPP, and SWYCC
employees who contributed to this project.
Funding was provided, in part, by the USDA
Prevention, Suppression, and Restoration
Program.
Cankers were removed using pole pruners
(pictured), pole saws, pruning saws, and pole
chainsaws. We attempted to remove all cankers
indicated for removal by the assigned treatment
that were accessible and could be safely removed
with our equipment.
Field crews from the South-western Youth
Conservation Corps helped with data collection
and pruning.
References Blodgett, J. T. and K. F. Sullivan.
2004. First report of white pine blister rust on
Rocky Mountain bristlecone pine. Plant Disease
88311. Blodgett, J. T. and K. S. Burns. Letter
to the Superintendent of Great Sand Dunes
National Monument and Preserve, July 7, 2004.
Hagle, S.K, McDonald, G.I., and Norby, E.A.
1989. White pine blister rust in northern Idaho
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Research Station, Ogden, Utah. General Technical
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