1

Research Note RMRS-RN-44. 2011

v

v

Rocky Mountain Research Station

Research Note

Citation:

Crump, Amanda; Jacobi, William R.; Burns, Kelly S.; Howell, 

Brian E. 2011. Pruning to manage white pine blister rust in 

the southern Rocky Mountains. Res. Note RMRS-RN-44. Fort 

Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 10 p.

Authors:

Amanda Crump and William R. Jacobi are with the Department 

of Bioagricultural Sciences and Pest Management, Colorado 

State University, Fort Collins, Colorado.

Kelly S. Burns and Brian E. Howell are with the USDA Forest 

Service, Rocky Mountain Region, Lakewood Service Center, 

Golden, Colorado.

United States Department of Agriculture

Forest Service

Rocky Mountain Research Station

Research Note RMRS-RN-44

July 2011

Pruning to Manage White Pine Blister Rust in the 

Southern Rocky Mountains

Amanda Crump, William R. Jacobi, Kelly S. Burns, and Brian E. Howell

Abstract: White pine blister rust is an exotic, invasive disease that severely damages and kills white pines in the southern Rocky Mountains. 

We evaluated the efficacy of preventive pruning (removing lower 

branches) and/or sanitation pruning (removing cankered branches) 

to reduce disease impacts in limber (Pinus flexilis James) and Rocky 

Mountain bristlecone (P. aristata Englm.) pine in two recreation areas 

in the southern Rocky Mountains. We compared the benefits of the 

different pruning techniques based on the distribution and severity of 

cankers, tree height class (small = <20 ft, medium = 20 to 30 ft, and 

tall = >30 ft), and treatment feasibility and time. Preventive pruning 

removed less than half of all cankers at both sites. The most effective 

treatment, sanitation pruning, removed 98 to 100 percent of visible 

cankers. Cankers were located throughout tree crowns, and medium 

and tall trees had high incidences of cankers in the upper crown. 

Threatening cankers (cankers located on branches within 1 ft of or on 

the main stem) were common throughout the crowns of trees less than 

30 ft tall. In 5 to 10 minutes per tree, crews reliably removed cankers 

up to 25 ft with ground based tools. Small and medium-sized trees will 

benefit most from pruning because nearly all threatening cankers can 

be removed with reasonable effort.

Keywords: trimming, Cronartium ribicola, Pinus flexilis, Pinus aristata, 

disease management

Introduction

Limber pine (Pinus flexilis James) and Rocky Mountain 

(RM) bristlecone pine (P. aristata Englm.) are important species in the southern Rocky Mountains. They provide food and 

structure for wildlife, stabilize slopes, help regulate snow retention and runoff, and maintain cover on harsh, rugged sites 

where little else can grow (Schoettle 2004). White pine blister 

rust (WPBR), caused by the exotic fungus Cronartium ribicola 

J.C. Fish, threatens white pine forests in many locations in the 

region. The fungus enters through needle stomata and spreads 

into branches. The resulting cankers eventually girdle branches 

and stems, which can rapidly kill small trees, reduce stand reproduction, and deform or kill larger trees. This can result in 

significant economic, aesthetic, and ecological impacts (Kearns 

and Jacobi 2007, McDonald and Hoff 2001). Management 

strategies to prolong the life of these trees on high-value sites 

have not been developed.

Pruning lower branches to prevent potentially lethal 

lower stem infections (preventive pruning), used alone or in 
2

Research Note RMRS-RN-44. 2011

combination with the process of selectively removing cankers 

throughout the crown before they reach the main stem (sanitation pruning), may reduce the impacts of WPBR. Preventive 

pruning has been effective in commercially valuable white 

pine species such as western white pine (Pinus monticola 

Dougl. ex D. Don) (Hagle and Grasham 1988, Hagle and 

others 1989, Hunt 1998), eastern white pine (P. strobus 

L.) (Lehrer 1982), and sugar pine (P. lambertiana Dougl.) 

(O’Hara and others 2010). Preventive pruning is effective 

in these species because most lethal infections occur within 

the lower crown (generally below 8 ft) where environmental 

conditions are more conducive to infection (Hungerford and 

others 1982, Hunt 1982, Hunt 1991, Lehrer 1982, Stillinger 

1947, Van Arsdel 1961). Removing lower branches not only 

removes potentially lethal infections but also sites for future 

infection. Sanitation pruning is more costly than preventive 

pruning because more time, effort, and training are required 

to identify and remove cankers throughout tree crowns rather 

than just pruning to a set height.

Several researchers have evaluated the time and effort 

required to implement various pruning treatments for tree 

improvement and disease management. Foiles (1956) reported that it took one person-day, including administrative 

time, travel time, and rest periods, to preventively prune 128 

western white pines to 9 ft using hand and pole saws. Hagle 

and Grasham (1988) reported that it took one person-day 

to complete both preventive and sanitation pruning on 54 

western white pines in a 15- to 18-year-old plantation in 

Idaho. Studies in other northern Rocky Mountain conifer 

species found that standard pruning costs increase exponentially when pruning height exceeds operator height (O’Hara 

and others 1995). Information on the time and effort associated with pruning white pines for disease management in the 

southern Rocky Mountains is needed to develop appropriate 

treatment guidelines.

This study was conducted to evaluate the potential for using pruning as a tool to prolong the life of high-value limber 

and RM bristlecone pines in areas impacted by WPBR in the 

southern Rocky Mountains. The specific objectives were to: 

(1) evaluate the distribution and severity of WPBR cankers 

by tree size, (2) determine the feasibility and time required to 

carry out pruning treatments, and (3) compare the benefits 

of various pruning techniques based on canker severity and 

distribution, tree size, and treatment time and feasibility. This 

study also establishes an opportunity to monitor the longterm effectiveness of pruning for reducing lethal infections 

and extending the life of treated limber and RM bristlecone 

pines.

Materials and Methods

Study Sites

Vedauwoo Campground is located in the Medicine Bow 

National Forest in southeastern Wyoming along Interstate 80. 

The campground lies at 8200 ft in the transition zone between 

grasslands and forests composed predominately of limber 

pine in association with ponderosa (Pinus ponderosa Dougl. 

Ex Laws.) and lodgepole pine (P. contorta Dougl. ex Loud.) 

(Peet 1981). The limber pine ecosystems in this area are heavily 

impacted by WPBR but the disease has only been present for 

two to three decades (Geils, personal communication; Kearns 

2005).

The Mosca Pass site is located in the Great Sand Dunes 

National Park and Preserve in the Sangre de Cristo Mountains 

of south-central Colorado. The study area extends from 9400 

to 9700 ft in elevation along the upper mile of the Mosca Pass 

Trail. The forests are characterized by montane meadows where 

limber and RM bristlecone pine dominate hillsides mixed 

with ponderosa pine woodlands and white fir (Abies concolor

Gord, and Glend. Lindl) and Douglas-fir (Pseudotsuga menziesii [Mirbel] Franco) forests. WPBR was discovered in this 

area in 2003 (Blodgett and Sullivan 2004, Burns 2006) but 

the disease has likely been present since the early 1990s (Burns 

2006, Kearns and others 2008).

Tree Selection

Treatments were conducted in 2005 and 2006. Each site 

was divided into three blocks of approximately equal areas and 

available trees. We attempted to select three infected and three 

uninfected study trees in each of four diameter at breast height 

(dbh, 4.5 ft) classes (1 to 4 inches, greater than 4 to 8 inches, 

and greater than 8 inches) per block. Large-diameter trees were 

scarce in some blocks so additional trees were included in the 

other diameter classes to meet a minimum target of nine infected trees per treatment. Extra trees were included when feasible 

to ensure a minimum number would survive over time. This 

resulted in 167 to 197 treated study trees per site, including at 

least 108 infected (36 trees in each block) and 54 uninfected 

(18 trees in each block) trees. All study trees were randomly 

assigned one of four treatments (see the “Pruning and Canker 

Removal Treatments” section).

Data collected for each study tree were tree height, dbh 

(4.5 ft), age via increment cores at 4.5 ft, number of cankers 

removed, evaluation time, treatment time, and information on 

the number, height distribution, size, and status of WPBR cankers. Treatment time included training field crews, evaluating 

tree health, and applying treatments.
3

Research Note RMRS-RN-44. 2011

Operational data were also collected in the Vedauwoo 

Campground. All limber pines within the Vedauwoo 

Campground were treated operationally with the exception of 

a subset of trees that were randomly selected as study trees. 

Only study trees were selected in the Mosca Pass study area. 

Operational trees were assigned a treatment based on the pruning crew’s judgment. Crew members selected the treatment 

that they presumed to be most effective given the tree’s size 

and the distribution and severity of cankers. Data collected 

for these trees included the number of cankers and treatment 

times. All uninfected operational trees received the preventive 

pruning treatment.

Frequency counts, percentage, and means were summarized 

by location for descriptive variables—tree age, height, dbh, and 

percent live crown; percent of cankers removed by treatment; 

average time to conduct treatments; and the distribution of 

cankers by height in crowns using PROC FREQ and PROC 

MEANS in SAS/Stat Version 9.2 (SAS Institute, Cary, North 

Carolina). PROC GLM was used to fit a one-way general linear model to estimate least squares means of the total time 

needed for rating and pruning for the various treatment effects. The total time in minutes was transformed by square root 

to account for skewed data. Pair-wise comparisons between 

treatments were done with t-test since the treatment effect was 

significant (P≤0.05)

Pruning and Canker Removal Treatments

Each tree was assigned one of four treatments:

1. No treatment.

2. Preventive pruning (pruning all branches flush with the 

branch collar, up to 7 ft or 40 percent of the live crown, 

whichever was less).

3. Preventive pruning and sanitation pruning/canker excising 

(removal of all visible cankers).

4. Sanitation pruning/canker excising.

Branch cankers located more than 4 ft from the main stem 

were removed 1 ft down the branch from the leading edge of 

the canker if the remaining branch had foliage (partial branch 

removal). The entire branch was removed if the canker was 

within 4 ft of the main stem. Cankers were considered threatening if they were on the main stem or located on a branch 

within 1 ft of the main stem (to account for proximal branch 

canker expansion). If stem cankers impacted less than 40 percent of the stem’s circumference, they were excised by removing 

the bark at least 3 inches outside of the canker margin. Trees 

were considered fatally infected if they had stem cankers that 

would girdle and kill the tree or if removal of extensive branch 

cankers would remove over 50 percent of the crown. Trees 

that were fatally infected with WPBR were excluded from the 

study. WPBR cankers were confirmed by the presence of aecia 

blisters; if aecia were not visible, at least two of the following 

indicators had to be present: discoloration, abnormal swelling, 

expanding areas of rodent chewing, flagging, and evidence of 

past blistering (roughened bark).

Crews and Tools

Crews of two to three people surveyed and treated trees. One 

crew member recorded data and the remaining members took 

field measurements and applied treatments. Crews used 10- to 

14-inch folding or rigid handsaws to remove lower branches. 

Cankers that were higher in the crown were removed with extendable pole pruners and pole saws. Gas-powered chain saws 

with extendable poles were used at Vedauwoo Campground. 

Scribing knives were used to excise stem cankers.

Results

Limber pine was the predominant tree species (59.3 percent) in Vedauwoo Campground. The remaining trees were 

ponderosa pine (35.7 percent), Douglas-fir (2.2 percent), 

quaking aspen (Populus tremuloides Michx.) (1.7 percent), 

lodgepole pine (0.6 percent), subalpine fir (Abies lasiocarpa

[Hook.] Nutt.) (0.3 percent), and Engelmann spruce (Picea

engelmannii Parry ex Engelm.) (0.2 percent). Eighty percent of 

surveyed limber pines were infected with WPBR and 33 percent (221 of 677 trees) had been killed by the disease. Within 

the campground, 410 limber pines were treated, including 213 

operational and 197 study trees. A complete disease incidence 

survey was not completed at Mosca Pass. However, a 2004 

survey found an average disease incidence in the area of 14 percent, and 60 percent of infected trees had threatening cankers 

(Burns 2006). Fourteen (9 percent) of the study trees at Mosca 

Pass were RM bristlecone pines and 153 (91 percent) were limber pines. Mosca Pass and Vedauwoo Campground trees were 

similar in average dbh (8.0 and 8.1 inches, respectively) and 

height (23.5 and 24.7 ft) but differed substantially in age (50.9 

and 86.5) and percent live crown (86.6 percent and 69.4 percent), respectively (Table 1).

Distribution and Severity of Cankers

WPBR cankers were located throughout tree crowns at both 

locations. The percentage of cankers occurring in the upper 

half of the crown for small (<20 ft), medium (20 to 30 ft), and 

tall (>30 ft) trees was 67, 70, and 76 percent, respectively, at 
4

Research Note RMRS-RN-44. 2011

Vedauwoo Campground and 48, 51, and 70 percent, respectively, at Mosca Pass (Figures 1 and 2). Threatening cankers 

were located throughout the crown of small trees at Mosca Pass 

but were more frequent in the upper half of the crowns of small 

trees at Vedauwoo Campground. Threatening cankers occurred 

mainly in the upper crown of medium (70 and 77 percent) and 

large trees (100 and 82 percent) at Mosca Pass and Vedauwoo 

Campground, respectively (Figure 2).

Most branch cankers were located far from the stem and 

therefore were not considered threatening cankers. The average 

distance of branch cankers from the main stem increased by 

tree height class at both sites and was 2.6 ± 2.0 ft (standard error) and 3.3 ± 2.8 ft for small trees, 5.0 ± 3.3 ft and 4.6 ± 3.1 ft 

for medium trees, and 6.8 ± 2.9 ft and 5.9 ± 3.8 ft for large 

trees at Mosca Pass and Vedauwoo Campground, respectively.

Treatment Time and Feasibility

Based on the operational treatments conducted in this 

study, it is feasible for one person to locate, rate, and prune 

(preventive and/or sanitation) at least 32 trees in a typical work 

day, including travel time and rest periods (Table 3). It took 30 

to 35 minutes per tree to apply treatments and record extensive 

data but only 5 to 10 minutes per tree to apply treatments 

to operational trees (Table 2). The average treatment time per 

tree for all pruning treatments combined was 4.9 ± 0.6 to 

10.1  ±  1.8 minutes while operational treatments took 8.0 ± 

0.6 minutes per tree. Data recording in an operational program 

would be minimal and the efficiency of the project would be 

much better than the values noted in Tables 2 and 3.

Generally, treatments took longer to implement at Mosca 

Pass since the terrain was more rugged and we were restricted 

to using manual equipment (Table 3). Treatments 1, 2, and 4 

took significantly less time than treatment 3 on infected trees at 

Vedauwoo Campground, but there were no significant differences in times between the various treatments for infected trees 

at Mosca Pass. The time required to rate and prune healthy 

trees ranged from 5 to 11 minutes (Table 3).

Hand saws were the preferred tool for preventive pruning. 

Sanitation pruning was easiest in the lower crown with extension pole side-cutting pruners. Crews were able to remove 

cankers below 25 ft and occasionally as high as 34 ft although 

tools became difficult to maneuver above 15 ft. Gas-powered 

chain saws on extended poles were effective at removing cankers up to 15 ft but required more skill to operate. Fortunately, 

pruned branches were fairly small and easy to cut, averaging 

3.0 ± 0.2 SE inches in diameter at the stem for total branch 

removals and 1.0 ± 0.1 SE inches for partial branch removals.

Benefits of Pruning

Preventive, preventive and sanitation, and sanitation treatments removed 21, 92, and 100 percent of all cankers from 

trees at Vedauwoo Campground, respectively, and 45, 98, and 

98 percent of all cankers at Mosca Pass, respectively (Table 4). 

Preventive pruning was the least effective treatment overall and 

was ineffective for removing threatening cankers from medium 

and tall trees and moderately effective for removing threatening cankers from small trees (Table 4). Sanitation pruning 

removed the most cankers (98 to 100 percent) (Table 2). When 

sanitation pruning was combined with preventive pruning, the 

percentage of cankers removed was slightly lower in some tree 

size classes. The slightly lower percent of cankers removed was 

not because of the combined effort because of the type of trees 

and canker distribution that happened to be in that population 

of trees were harder to reach and remove.

The percentage of cankers within the preventive pruning 

height (lower 7 ft or 40 percent of the crown, whichever was 

less) on small, medium, and tall trees was 52, 24, and 7 percent at Mosca Pass, respectively, and 47, 12, and 5 percent 

at Vedauwoo Campground, respectively. These lower cankers accounted for 42 percent of all cankers at Mosca Pass 

and 21  percent of all cankers at Vedauwoo Campground. 

Therefore, preventive pruning removed less than half of all 

cankers at Mosca Pass and less than one quarter of all cankers 

at Vedauwoo Campground.

Discussion

Branch cankers and threatening cankers were distributed 

throughout the crowns of limber and RM bristlecone pine of 

all sizes in the southern Rocky Mountains. On trees greater 

than 20 ft tall, most branch cankers were located far from the 

main stem and above standard pruning height, and the majority of threatening cankers were located in the upper crown. 

On trees less than 20 ft tall, approximately half of all cankers 

Table 1. Attributes of limber and RM bristlecone pine study trees at 

Mosca Pass, Colorado, and Vedauwoo Campground, Wyoming, 

2005 to 2006.

Mosca Pass Vedauwoo Campground

n = 167 n = 197

Mean (SE) Mean (SE)

Age (yr) 50.9 (± 2.2) 86.5 (± 2.2)

Height (ft) 24.7 (± 0.3) 23.5 (± 0.4)

dbh (in) 8.0 (± 0.28) 8.1 (± 0.30)

Percent live crown (%)

 Uninfected trees 86.6 (± 3.8) 69.4 (± 3.9)

 Infected trees 86.0 (± 4.1) 69.0 (± 4.1)
5

Research Note RMRS-RN-44. 2011

Figure 1. General depiction of all white pine blister rust branch and stem canker locations in crowns of small, medium, and tall trees in Mosca 

Pass, Colorado, and Vedauwoo Campground, Wyoming. Mosca Pass total cankers n = 687; small tree n = 74, cankers n = 218; medium 

tree n = 53, cankers n = 306; tall trees n = 40, cankers n = 163. Vedauwoo campground total cankers n = 948; small tree n = 97, cankers n 

= 255; medium tree n = 76, cankers n = 416; tall trees n = 21, cankers n = 245.
6

Research Note RMRS-RN-44. 2011

Figure 2. General depiction of white pine blister rust threatening canker (stem cankers and branch cankers within 1 ft of the main stem) 

locations in crowns of small, medium, and tall trees in Mosca Pass, Colorado, and Vedauwoo Campground, Wyoming. Mosca 

Pass total cankers n = 123; small tree n = 73, cankers n = 98; medium tree n = 53, cankers n = 44; tall trees n = 40, cankers n = 6. 

Vedauwoo campground total cankers n = 163; small tree n = 97, cankers n = 74; medium tree n = 76, cankers n = 62; tall trees n = 2, 

cankers n = 16.
7

Research Note RMRS-RN-44. 2011

Table 2. Average time and number of people needed to treat trees with preventive and sanitation pruning at Mosca Pass, 

Colorado, and Vedauwoo Campground, Wyoming.

Location

Mosca Pass Vedauwoo Campground Vedauwoo Campground

study trees study trees operational trees

Trees treated per day by crew 23.8 39.2 66c

Crews per day 2.3 1.8 2.3

People per crew 3.7 3.2 3.5

Person-hours per daya 32 39.6 37.1

Time to apply treatments 2 through 4/tree (min.)b 10.1 4.9 8.0

Time to gather data/tree (min.) 12.2 7.3 nad

Total time to locate, rate, and treat each tree (min.) 34.8 30.0 14.4

a Person-hours per day: total number hours worked by personnel each day (for example, at Mosca Pass, 2.3 crews of 3.7 people 

took 32 hours to treat 23.8 trees per day, on average). b Because treatment 1 was “no treatment,” it was not included.

c Operational trees treated per day included trees with no treatment needed and excluded trees that were too diseased to warrant 

treatment. d na = no data were collected on the cankers on these operational trees.

occurred within the standard pruning height and were much 

closer to the main stem, but threatening cankers were common 

throughout their crowns. These distribution patterns suggest 

that the urgency for treatment is greatest in small trees.

We found that one worker can treat approximately 32 trees 

per day in an operational mode. This level of productivity seems 

reasonable for high-value limber and RM bristlecone pines 

even though significantly more time and effort was required 

for these species than was required for similar treatments documented in other white pine species. The wide distribution of 

cankers within tree crowns of limber and RM bristlecone pine 

requires more skill for identification and removal, and rugged 

terrain is typical where these species grow. Smaller trees (less 

than 25 ft tall) are optimum candidates for treatment because 

cankers can be identified more effectively and the entire crown 

can be reached with ground based equipment. The optimum 

time for locating cankers is in early summer when rust sporulation makes cankers easier to locate.

Obviously, pruning to a set height requires less skill and, 

therefore, would likely be easier to implement. However, 

preventive pruning would likely provide little long-term benefit to limber or RM bristlecone pine in the southern Rocky 

Mountains, regardless of tree size. In the short term, it could 

prevent some threatening cankers from girdling the main 

stem but many cankers would be missed in the upper crown. 

Preventive pruning is successful in other regions on other white 

pine species in part because most infections occur in the lower 

crown (Hunt 1998). In those ecosystems, diurnal fog cycles 

take place close to the ground, creating favorable conditions 

for infection (Hunt 1998, Van Arsdel 1961). Limber pine and 

RM bristlecone pine often occur in open woodland ecosystems 

where humidity events near the ground are rare. However, 

Table 3. Average time to assess and treat trees according to pruning treatment applied at Mosca Pass, Colorado, and Vedauwoo 

Campground, Wyoming.

Location

Mosca Pass Vedauwoo Campground

Trees with time (95% Trees with time (95%

recorded/total confidence recorded/ total confidence

Treatment a trees (n/n) Minutesb interval) trees (n/n) Minutesb interval)

1–Infected trees 17/30 14.5ab (10.1-19.6) 28/34 8.9bc (6.6-11.5)

2–Infected trees 8/24 13.4ab (7.63-20.9) 31/31 8.6bc (6.4-11.0)

3–Infected trees 15/27 19.7 b (14.3-26.0) 29/29 14.4d (11.5-17.6)

4–Infected trees 15/28 22.9 b 17.0-29.7) 34/34 11.3cd (8.9-13.9)

1–Healthy trees 13/26 10.4a (6.3-15.5) 28/33 4.7a (3.1-6.6)

2–Healthy trees 12/31 11.4 a (7.6-15.9) 30/35 6.1ab (4.4-8.2)

a Treatment 1–No treatment; Treatment 2–Preventive pruning (removing all branches up to 7 ft or 40 percent of the live crown); 

Treatment 3–Preventive and sanitation pruning; Treatment 4–Sanitation pruning (removal of all visible cankers). Treatment 1 

and 2 on healthy trees were “No treatment” and “Preventive pruning,” respectively. b

 Minutes: time to assess and treat–means followed by same letter within a location are not significantly different based on 

pair wise t-test (P<0.05). No analysis is provided to compare between locations since the conditions, crew, and trees were 

different at each location.
8

Research Note RMRS-RN-44. 2011

large-scale weather systems settle over these ecosystems infrequently, creating favorable conditions for infection extending 

above the height of the relatively short white pines of the region (Jacobi and others 2002).

Epicormic branches and needles growing on lower stems 

and larger branches of trees shorter than 20 ft is common in 

white pines of the region. These short branches and needles 

offer the WPBR fungus a direct entrance to the main stem 

since the needles are within 0.5 inches of the stem. Thus, even 

though traditional preventive pruning may not be warranted as 

such, we recommend it on trees shorter than 20 ft, and we recommend removing epicormic branches and needles that occur 

within a foot of the main stem on all trees while implementing 

treatments. This is very easy to do with small hand saws or 

clippers while implementing sanitation pruning, and it will reduce the chance of these highly susceptible branches becoming 

infected and girdling the main stem.

Sanitation pruning is likely the most effective treatment option for all size classes, but treatments are most warranted and 

will be most successful on trees less than 25 ft tall. Preventive 

pruning missed a large number of cankers located above the 

standard pruning height, and there was no added benefit when 

sanitation and preventive pruning were combined. Proximal 

canker expansion is only about 2 to 5 inches per year, so the 

efficacy of branch canker removal in upper tree crowns is questionable (Kearns and others 2008). However, serious decline, 

mortality, and loss of cone bearing branches occur when trees 

have many branch infections, and seriously weakened trees 

may become susceptible to various bark beetles and canker 

diseases. Initially, there was concern that pruning might attract 

bark or twig beetles, but we found no evidence of any type of 

bark beetle attacks directly related to treatments or other stresses three years after treatment at Mosca Pass and Vedauwoo 

Campground. (Data not shown.)

Complete sanitation of infected trees greater than 25 ft tall 

is unlikely due to the high incidence of cankers in the upper 

crown. These larger limber pines also typically have a broad 

and often multi-stemmed growth form that increases the difficulty of identifying infections and applying treatments. A 

high-lift device that supplements ground based equipment 

would be useful for removing cankers in the upper portions 

of larger trees.

Using volunteers and workers who are not trained in arboricultural activities proved to be adequate for pruning trees. The 

amount of training and follow up work with these crews varied 

depending on their interest in the project. Understanding the 

infection process and colonization by the rust fungus helped 

ensure proper treatments were applied.

Conclusion

The decision to implement pruning treatments must be 

weighed against the value of keeping trees on these sites. In 

many recreation areas in the southern Rocky Mountains, 

limber and RM bristlecone pine are a major, if not sole, tree 

component. These trees are subjected to tremendous stress by a 

multitude of factors such as severe site and weather conditions, 

Table 4. Percent of white pine blister rust cankers removed by pruning at Mosca Pass and Vedauwoo Campground, 2005 to 2006.

Pruning treatment

Preventive Preventive and sanitation Sanitation

Threatening Threatening Threatening

Study site All cankersa cankersb All cankers cankers All cankers cankers

Tree size % % % % % %

Mosca Pass

Small trees 75 74 98 96 98 100

Medium trees 47 0 98 90 100 100

Tall trees 14 nac 98 na 96 na

Overall 45 37 98 93 98 100

Vedauwoo Campground

Small trees 44 44 92 88 100 100

Medium trees 10 0 98 97 99 100

Tall trees 9 0 86 56 100 na

Overall 21 15 92 80 100 100

a All cankers: Mosca Pass total cankers n = 687; small tree n = 74, cankers n = 218; medium tree n = 53, cankers n = 306; 

tall tree n = 40, cankers n = 163; Vedauwoo campground total cankers n = 948; small tree n = 97, cankers n = 255; medium tree 

n = 76, cankers n = 416; tall trees n = 21, cankers n = 245. b Threatening cankers: Mosca Pass total cankers n = 123; small tree n = 73, cankers n = 98; medium tree n = 53, cankers n = 44; 

tall trees n = 40, cankers n = 6; Vedauwoo campground cankers n = 163; small tree n = 97, cankers n = 74; medium tree n =76, 

cankers n = 62; tall trees n = 21, cankers n = 16. c na = no threatening cankers occurred in this tree size class and treatment combination.
9

Research Note RMRS-RN-44. 2011

WPBR, heavy recreational use, and bark beetles that impact tree 

vigor and regeneration rates. WPBR cankers occur throughout 

the crown, and some cankers in the tops of crowns were difficult to remove with standard pruning equipment; however, 

most threatening cankers can be removed with reasonable effort on smaller trees. Thus, sanitation pruning on all trees, with 

preventative pruning on trees 20 ft or shorter to remove small 

and epicormic branches, repeated every five years may be a viable management option for maintaining high-value trees for 

gene conservation or landscape use on recreation sites in the 

southern Rocky Mountains. Treated trees should be monitored 

frequently following treatment, and treatments may need to 

be repeated every three to five years to remove missed or new 

cankers if WPBR incidence and severity is high at a specific location. If there are limited resources, repeat treatments should 

focus on large trees that add the greatest value to the site and on 

smaller trees since branch cankers can easily become threatening and girdle the tree.

Major points for operational pruning:

•	 Pruning limber pine trees to prevent WPBR mortality is 

primarily feasible for high-value trees such as those in 

campgrounds and similar locations.

•	 Sanitation pruning coupled with removal of epicormic 

branches and needles can be carried out on trees less than 

25 ft tall with ground based pruning equipment.

•	 The time needed to prune trees is 5 to 10 minutes, but it 

could be more depending on the tree height and number 

of cankers.

•	 Pruning should be done when the orange aecial blisters are 

visible—usually June 1st through the 20th.

•	 Pruning and careful inspection should be carried out at 

three- to five-year intervals depending on the incidence and 

severity of the rust.

•	 Pruning should not be attempted on trees with cankers on 

more than 50 percent of the branches because the tree will 

probably not survive the removal of that much of the crown.

Acknowledgments

We thank Phyllis and Ola Bovin, Jim Worrall, Brian Geils, 

Bob Cain, Clint Kyhl, Jennifer Klutsch, Russell Beam, Paul 

Blackman, Adriene Holcomb, Jim zumBrunnen, and all of the 

Laramie Ranger District, Great Sand Dunes National Park and 

Preserve, and Southwest Conservation Corps employees who 

contributed to this project. Funding was provided, in part, by 

the National Park Service, the United States Department of 

Agriculture Prevention, Suppression, and Restoration Program, 

and the Colorado Agricultural Experiment Station.

References

Blodgett, J.T.; Sullivan, K.F. 2004. First report of white pine 

blister rust on Rocky Mountain bristlecone pine. Plant 

Disease. 88:311.

Burns, K.S. 2006. White pine blister rust surveys in the Sangre 

de Cristo and Wet Mountains of southern Colorado. U.S. 

Department of Agriculture, Forest Service, Rocky Mountain 

Region, Bio. Eval. R2-06-05. 22 p.

Foiles, M.W. 1956. Time required to prune crop trees in the 

western white pine type. U.S. Department of Agriculture 

Forest Service, Intermountain Forest and Range Experiment 

Station, Res. Note. INT-32.

Geils, B.W. Research Plant Pathologist, U.S. Department 

of Agriculture, Forest Service, Rocky Mountain Research 

Station.

Hagle, S.K.; Grasham, J.L. 1988. Biological and economic feasibility of pruning and excising white pines for blister rust 

control. U.S. Department of Agriculture, Forest Service, 

Northern Region, Pest Management.

Hagle, S.K.; McDonald, G.I.; Norby, E.A. 1989. White 

pine blister rust in northern Idaho and western Montana: 

Alternatives for Integrated Management. U.S. Department 

of Agriculture, Forest Service, Intermountain Forest and 

Range Experiment Station. Gen. Tech. Rep. INT-261. 35 p.

Hungerford, R.D.; Williams, R.E.; Marsden, M.A. 1982. 

Thinning and pruning western white pine: A potential for 

reducing mortality due to blister rust. U.S. Department 

of Agriculture, Forest Service, Intermountain Forest and 

Range Experiment Station. Res. Note. INT-322. 7 p.

Hunt, R.S. 1982. White pine blister rust in British-Columbia 

1. The possibilities of control by branch removal. Forestry 

Chronicle. 58:136-138.

Hunt, R.S. 1991. Operational control of white pine blister 

rust by removal of lower branches. Forestry Chronicle.

67:284-294.

Hunt, R.S. 1998. Pruning western white pine in British 

Columbia to reduce white pine blister rust losses: 10-year 

results. Western Journal of Applied Forestry. 13:60-63.

Jacobi, W.R.; Geils, B.W.; Taylor, J.E. 2002. Frequency of comandra blister rust infection episodes on lodgepole pine. 

U.S. Department of Agriculture, Forest Service, Rocky 

Mountain Research Station. Res. Pap. RMRS-RP-36. 13 p.
10

Research Note RMRS-RN-44. 2011

Kearns, H.S.J. 2005. White pine blister rust in the central 

Rocky Mountains: Modeling current status and potential impacts. Dissertation. Colorado State University. Fort 

Collins, CO, USA. 243 p.

Kearns, H.S.J.; Jacobi, W.R. 2007. The distribution and incidence of white pine blister rust in central and southeastern 

Wyoming and northern Colorado. Canadian Journal of 

Forest Research. 37:1-11.

Kearns, H.S.J.; Jacobi, W.R.; Geils, B.W. 2008. A method 

for estimating white pine blister rust canker age on limber 

pine in the central Rocky Mountains. Forest Pathology. 

39:177-191.

Lehrer, G.F. 1982. Pathological pruning—A useful tool in 

white pine blister rust control. Plant Disease. 66:1138-1139.

McDonald, G.I.; Hoff, R.J. 2001. Blister rust: An introduced 

plague. P. 193-220 in: Tomback, D.F.; Arno, S.F.; Keane. 

R.E., eds. Whitebark Pine Communities: Ecology and 

Restoration. Island Press, Washington, DC.

O’Hara, K.L.; Grand, L.A.; Whitcomb, A.A. 2010. Pruning 

reduces blister rust in sugar pine with minimal effects on 

tree growth. California Agriculture. 64(1):31-36.

O’Hara, K.L.; Larvik, D.A.; Valappil, N.I. 1995. Pruning costs 

for four northern Rocky Mountain species with three equipment combinations. Western Journal of Applied Forestry. 

10(2):59-65.

Peet, R.K. 1981. Forest vegetation of the Colorado Front 

Range: Composition and dynamics. Vegetation. 45:3-75.

SAS Institute Inc. 2004. SAS/STAT 9.1 user’s guide. Cary, NC: 

SAS Institute Inc.

Schoettle, A.W. 2004. Ecological roles of five-needle pine in 

Colorado: Potential consequences of their loss. P. 124-135 

in: Sniezko, R.; Samman, S.; Schlarbaum, S.; Kriebel, H., 

eds. Breeding and genetic resources of five-needle pines: 

Growth, adaptability, and pest resistance. 2001 July 24-25; 

Medford, OR. IUFRO Working Party 2.02.15. Ogden, 

UT: U.S. Department of Agriculture, Forest Service, Rocky 

Mountain Research Station. Proc. RMRS-P-32.

Stillinger, C.R. 1947. Pruning white pine reproduction to salvage a stand heavily infested with white pine blister rust. 

U.S. Department of Agriculture, Bureau of Entomology 

and Plant Quarantine. Serial 138. 21 p.

Van Arsdel, E.P. 1961. Growing white pines in the Lake States 

to avoid blister rust. U.S. Department of Agriculture, Forest 

Service, Lake States Forest Experiment Station. Paper No. 

92. 11 p.
You may order additional copies of this publication by sending your 

mailing information in label form through one of the following media. 

Please specify the publication title and series number.

Publishing Services

Telephone (970) 498-1392

FAX (970) 498-1122

E-mail rschneider@fs.fed.us

Web site http://www.fs.fed.us/rm/publications

Mailing address Publications Distribution

Rocky Mountain Research Station

240 West Prospect Road

Fort Collins, CO 80526
Federal Recycling Program Printed on Recycled Paper

Rocky

 Mountain

 Research Station

The Rocky Mountain Research Station develops scientific information 

and technology to improve management, protection, and use of the 

forests and rangelands. Research is designed to meet the needs of 

the National Forest managers, Federal and State agencies, public and 

private organizations, academic institutions, industry, and individuals. 

Studies accelerate solutions to problems involving ecosystems, range, 

forests, water, recreation, fire, resource inventory, land reclamation, 

community sustainability, forest engineering technology, multiple use 

economics, wildlife and fish habitat, and forest insects and diseases. 

Studies are conducted cooperatively, and applications may be found 

worldwide.

Station Headquarters

Rocky Mountain Research Station

240 W Prospect Road

Fort Collins, CO 80526

(970) 498-1100

Research Locations

Reno, Nevada

Albuquerque, New Mexico

Rapid City, South Dakota

Logan, Utah

Ogden, Utah

Provo, Utah

The U.S. Department of Agriculture (USDA) prohibits discrimination in all its 

programs and activities on the basis of race, color, national origin, age, disability, 

and where applicable, sex, marital status, familial status, parental status, religion, 

sexual orientation, genetic information, political beliefs, reprisal, or because all 

or part of an individual’s income is derived from any public assistance program. 

(Not all prohibited bases apply to all programs.) Persons with disabilities who 

require alternative means for communication of program information (Braille, 

large print, audiotape, etc.) should contact USDA’s TARGET Center at (202) 

720-2600 (voice and TDD). To file a complaint of discrimination, write to USDA, 

Director, Office of Civil Rights, 1400 Independence Avenue, S.W., Washington, 

DC 20250-9410, or call (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA 

is an equal opportunity provider and employer.

Flagstaff, Arizona

Fort Collins, Colorado

Boise, Idaho

Moscow, Idaho

Bozeman, Montana

Missoula, Montana