This file was created by scanning the printed publication.
Errors identified by the software have been corrected;
however, some errors may remain.
Conllnandra Blister Rust: A Threat to
Lodgepole Pin.e
Brian W. Geils and William R. JacobP
Abstract--Comandra blister rust Is an Important canker disease of
lodgel)ole pine In the central Rocky Mountains. Current research is quantifying the rlsl< of serious disease outbreaks and the ma~lnitude of resultin~1 losses. Bust Incidence in lod~lepole pine stands is related to the
distance and direction from the alternate host and average tree height.
Projected losses are Influenced by both stand and disease conditions
such as percent of trees Infected and average canker height.
Comandra blister rust (Cronartium comandrae) causes
stem and branch cankers on several species of pine.s, including
lodgepole pine (Johnson 1986). These cankers are resi.nous
areas which produce orange spores that spread the fungus to
an alternate host, but not to other pines. Eventually, a canker
girdles the host stem, killing all. or part of the crown.
Comandra blister rust occ.urs throughout most of North
America, and is a serious cause of loss in many lodgepole pine
forests, especially in the central Rocky Mountains. For example, more than half of the lodgepole pine basal area is in
infected trees on the 'Vind River District of the Shoshone
National Forest (Geils and Jacobi 1984).
Comandra blister rust has a complex life cyde with five
different spore stages produced alternately on two hosts -- a
hard pine and the perennial herb for which the fungus is
named, pale comandra (Col1umdra umbellata).
the lodgepole pi.ne host. A risk rating system provides the
means to esti.mate the probability of a rust infestation occurring in a given stand during a fixed period.
A few biological factors are important for dete.rmining
risk. First, the spores that infect the pine are produced only on
comandra plants. These plants occur in sagebrush communities at va;io~s distances from the pine stands. The de.Iicate rust
spores are wind-dispersed from the comandra plants to pines
during rainy days in late summer. And finally, the. primary
infection sites on pines are young, succulent shoots and
needles (Krebill1968).
We are using historical and on-site weather data to determine the frequency of weather events optimal for spore
dispersal and pine infection. These data also provide information on wind direction and speed during spore flight.
The distribution of both host species, disease incide.nce,
and patterns of wind flow are being mapped for the southe.rn
portion of the Laramie District, l\ledicine Bow National
Forest, in southeast '''yoming. The lodgepole pine on this
district is bordered on the east and west by plant communities
in which pale comandra occurs.
Within the narrow range of available stand ages, inventory
data for lodgepole pine are· being analyzed to correlate stand
and site conditions (density, hei.ght, age, crown size, site index,
habitat type) with disease i.ncide.nce and seve.rity. Together
with location and weather data, this information is bei.ng used
to predict the gradient of disease intensity and to classify sites
for risk of infection.
Our preliminary re·sults indicate that:
Objectives
The purpose of this cooperative effort was to develop
management tools for predicting:
1. Risk of serious disease outbreaks in stands of
lodgepole pine in the Rocky l\lountains.
2. Magnitude of damage-re.lated losses to forest resources.
Predicting Risk
Although millions of rust spores are produc.ed annually on
ea.ch disease.d comandra plant, only a few of the·se spores are
likely to infect and subsequently cause damaging cankers on
1. Pine stands as far as 8 miles from comandra plants
can be seriously infected.
2. Spore dispersal from comandra plants to pines
seems to be associated with easterly winds during
long, rainy periods.
1Geils is a Research Plant Pathologist with the Flod<y Mountain
Forest and Range Experiment Station. Station headquarters is in Fort
Collins, in cooperation with Colorado State University. Jacobi is Associate
Professor of Plant Pathology, Colorado State University, Fort Collins.
216
and improving the individual growth of remaining trees. On
the other hand, high cankers kill fewer trees but leave the stand
overstocked.
3. Disease incidence increases with average tree
height.
Predicting Harnage
Future Work
The growth and yield program RMYLD (Edminster 1(78)
has recently been modified to account for the effects of
comandra blister rust on growth, survival, and merchantable
volume of lodgepole pine. Projections from this program can
be used to predict the exte·nt of damage resulting from a single
infection e.pisode. In the followi.ng example, damage is illustrated as loss of merc.hantable volume in a diseased stand in
comparison to a similar healthy stand.
A typical lodgepole pine stand in the Rocky :Mountain
Region (age 40, site index 60 feet) would contain about 715
trees pe.r acre with an a.verage diameter of 4.4 inches and an
average height of 27 feet. Without rust or thinning, the
R~fYLD program predicts the stand would produce 1070
cubic feet in 700 trees (dbh 5.~ inches) at age 60. The yield
pre.dictions suggest that the volume loss (due to tree mortality
and growth reduction in surviving trees) by age 60 would
depend mainly on the perce.ntage of trees infected at age 40:
Given a different set of initial conditions, losses to comandra bUste.r rust would change from those shown above. Additional work is in progress to project losse.s with more fre.que.nt
infection episodes in stands of various site, age, and stocking
conditions, and subject to a variety of manage.me.nt practice.s.
I
References
Edminster, Carleton B.1978. Rl\fYLD: Computation of yield
tables for even-aged and two-storied stands. Res. Pap.
Rl\f-199. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky' Mountain Forest and Range
Experiment Station. 26 p.
Geils, Brian '''.; Jacobi, \Villiam R. 1984t Incidence and
severity of comandra blister rust on lodgepole pine jn
northwestern Wyoming. Plant Disease. 68:.1049-1051.
Johnson, David V,l.1986. Comandra blister rust. Forest Insect
and Disease Leaf. 62. \Vashington, DC: U.S. Department
of Agriculture, Forest Service. 8 p.
Krebill, Richard G. 1968. Cronartium cOl1umdrae in the Rocky
J\.fountain States. Res. Pap. INT-50. Ogden, UT: U.S.
Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 28 p.
20% of trees infected = 5%) reduction in stand volume.
40% of trees infected = 20crb reduction in stand volume.
60% of trees infected = 40% reduction in stand volume.
80% of trees infected = 60% reduction in stand volume.
Average canker hei.ght has an effect on average diameter:
low cankers kill infected trees quickly, reducing competition,
217