CONTROL OF DWARF MISTLETOE
Robert F. Scharpf-2/
Abstract: The dwarf m i s t l e t o e A f e e u t ' h o b h abietinum
i s a s e r i o u s p a r a s i t e of t r u e f i r s [Abies spp.) growing
on t h e P a c i f i c Coast. Damage i s most severe i n old-growth
and unmanaged f i r stands. With information now a v a i l a b l e ,
t h e f o r e s t manager can develop management guides f o r
control of dwarf mistletoe. Such information includes
parasite-host s p e c i f i c i t y , s i z e a t which young t r e e s become infected, growth r a t e of t r e e s i n r e l a t i o n t o dwarf
m i s t l e t o e buildup and spread, and e f f e c t s of dwarf mistlet o e on t r e e growth r a t e and mortality.
INTRODUCTION
The t r u e f i r s (Abies spp.) a r e among t h e
more important commercial softwood timber
species i n t h e Western United S t a t e s . They
a r e not only widely u t i l i z e d i n t h e United
S t a t e s but a l s o a r e a valuable commodity i n
foreign timber markets. Unfortunately, f i r
stands i n t h e West a r e o f t e n severely i n f e s t e d
with dwarf m i s t l e t o e . This problem i s caused
almost e n t i r e l y by a s i n g l e species of dwarf
mistletoe--Arceuthob'Lum dbietiiwm.
The f i r s a r e abundant i n t h e West--particu l a r l y along t h e P a c i f i c Coast. In California,
f o r example, two f i r species--white f i r (Abies
eoncoZor), and red f i r (A. rnagnifica)--make up
about a t h i r d of t h e S t a t e ' s n e t cubic foot
volume--or about 15 b i l l i o n cubic f e e t out of
t h e estimated t o t a l n e t volume of 51 b i l l i o n
cubic f e e t of commercial softwood. The Western
S t a t e s combined contain a n e t volume of about
45 b i l l i o n cubic f e e t of t r u e f i r growing stock
(Anonymous 1972)
.
Dwarf m i s t l e t o e i s common on t r u e f i r s - p a r t i c u l a r l y i n C a l i f o r n i a and Oregon. Forest
Ñ'~resente a t t h e Symposium on Dwarf
Mistletoe Control Through Forest Managment,
Berkeley, C a l i f . , April 11-13, 1978.
Ñ'plan Pathologist, P a c i f i c Southwest
Forest and Range Experiment S t a t i o n , Forest
Service, U.S. Department of Agriculture,
Berkeley, C a l i f .
disease surveys conducted by t h e U.S. Forest
Service i n California i n the 1950's and 1960's
show t h a t t r u e f i r s a r e among t h e most heavily
i n f e s t e d commercial conifer species i n t h e
S t a t e . About 40 percent of t h e red f i r and
about 30 percent of t h e white f i r stands were
found t o be severely i n f e s t e d by dwarf m i s t l e toes (California Forest Pest Control Action
Council 1961). Thus, l i t e r a l l y thousands of
acres of pure f i r and mixed c o n i f e r stands
containing f i r species a r e infested with t h i s
parasite.
The l o s s e s of timber a t t r i b u t e d t o t h i s
p a r a s i t e i n f i r stands a r e not p r e c i s e l y known
but a r e estimated t o be enormous. For instance,
old-growth f i r s , i n p a r t i c u l a r , s u f f e r severe
losses. Reduction i n growth and vigor from
heavy infection, broken t r e e s r e s u l t i n g from
decay entering trunk infections, and m o r t a l i t y
caused by i n s e c t s attacking weakened t r e e s
account f o r much of t h e losses. Infected
t r e e s a r e a l s o more subject t o m o r t a l i t y from
other f a c t o r s , such a s root decay fungi and
moisture s t r e s s brought about by drought
conditions. The l o s s e s a t t r i b u t e d t o dwarf
m i s t l e t o e a r e not limited t o timber values
alone but a l s o a f f e c t r e c r e a t i o n a l and water
shed values a s well. Losses caused by dwarf
mistletoes either directly or indirectly w i l l
probably continue a t severe l e v e l s unless
many f i r stands i n t h e West a r e brought under
intensive management including dwarf m i s t l e t o e
control a s an i n t e g r a l p a r t of t h e management
plan.
PAST CONTROL EFFORTS
Within t h e l a s t decade o r two, c o n t r o l of
dwarf m i s t l e t o e i n t r u e f i r s has been attempted
almost e n t i r e l y by harvesting old-growth stands.
F i r stands, p a r t i c u l a r l y pure stands, were
harvested p r i m a r i l y by c l e a r c u t t i n g , o f t e n i n
l a r g e blocks. Unfortunately, f i r s do not nat u r a l l y reseed l a r g e c l e a r c u t a r e a s well, and
r e l i a b l e f i r p l a n t i n g stock has not always been
a v a i l a b l e f o r regenerating f i r s i t e s . Also,
o t h e r species s e l e c t e d f o r p l a n t i n g have not
developed well on pure f i r s i t e s - - J e f f r e y pines
i n C a l i f o r n i a , f o r example.
C l e a r c u t t i n g c o n t r o l l e d dwarf m i s t l e t o e
i n many a r e a s , but it has o f t e n created more
problems than it cured. Today, where c l e a r c u t t i n g is used, t h e t r e n d i s toward c u t t i n g
smaller blocks o r narrow s t r i p s i n order t o
o b t a i n n a t u r a l regeneration of f i r from adjacent stands. As good f i r p l a n t i n g stock becomes a v a i l a b l e , many c l e a r c u t a r e a s w i l l no
doubt a l s o be planted. Although dwarf m i s t l e t o e has been c o n t r o l l e d i n t h e p a s t by
c l e a r c u t t i n g i n many pure f i r stands, c l e a r c u t t i n g t o d a y - - p a r t i c u l a r l y over l a r g e areas-i s highly controversial--and many c l e a r c u t t i n g s
cause management problems more s e r i o u s than
dwarf m i s t l e t o e i n f e s t a t i o n . Therefore c l e a r c u t t i n g should n o t be considered t h e only sol u t i o n t o dwarf m i s t l e t o e control i n i n f e s t e d
f i r s t a n d s i n t h e West.
,
Kith some exceptions, control of dwarf
m i s t l e t o e i n mixed c o n i f e r stands with f i r ,
was almost e n t i r e l y overlooked o r disregarded
before about 1960. I n f a c t , because of e a r l y
logging p r a c t i c e s , t h e i n f e s t a t i o n by dwarf
m i s t l e t o e i n t h e s e mixed species stands has
probably gotten worse. For example, u n t i l
f a i r l y r e c e n t l y i n t h e West, f i r s were cons i d e r e d l e s s d e s i r a b l e than o t h e r c o n i f e r
species and commanded a r e l a t i v e l y low market
value. Thus, t h e higher value s p e c i e s , such
a s pines and Douglas-fir, were o f t e n s e l e c t i v e l y
logged, leaving t h e i n f e c t e d t r u e f i r component
of t h e stand behind. These r e s i d u a l f i r s o f t e n
seeded i n t o openings a f t e r logging. This pract i c e o f s e l e c t i v e l o g g i n g i n c r e a s e d t h e proport i o n of f i r s i n many stands. Dwarf m i s t l e t o e
was a b l e t o r e a d i l y spread from i n f e s t e d
overstory t o understory f i r t r e e s - - p a r t i c u l a r l y
i n t h e absence of pines and o t h e r nonsuscept i b l e t r e e species t h a t act a s barriers t o
spread o f seeds of t h e p a r a s i t e . Thus, I f e e l
c e r t a i n t h a t p a s t logging p r a c t i c e s i n many
mixed c o n i f e r s t a n d s has aggravated r a t h e r than
a l l e v i a t e d t h e dwarf m i s t l e t o e problem i n t r u e
firs.
PRESENT APPROACHES TO CONTROL
Enough information is now a v a i l a b l e t o
f o r e s t managers t o allow them t o develop guidel i n e s f o r c o n t r o l . A s more information becomes
a v a i l a b l e from research, management g u i d e l i n e s
can be improved and r e f i n e d . A v a r i e t y of
f a c t o r s bear on t h e development of g u i d e l i n e s
f o r control.
The P a r a s i t e is Host S p e c i f i c
I t has long been known t h a t t h e dwarf
m i s t l e t o e on t r u e f i r s is very host s p e c i f i c
(Parmeter and Scharpf 1963, Hawksworth and Wiens
1972). One of t h e problems t h a t confused
f o r e s t e r s i n t h e p a s t i s t h a t occasionally more
than one species of f i r was found t o be infected
i n some stands. Subsequent s t u d i e s have shown
t h a t f o r t h e most p a r t , only one dwarf m i s t l e t o e
species i n f e c t s f i r s , but it i s made up o f two
i n d i s t i n g u i s h a b l e p l a n t forms t h a t i n f e c t d i f f e r e n t f i r species. These forms cannot be
separated on t h e b a s i s of outward physical
c h a r a c t e r i s t i c s , but they can be separated on
t h e b a s i s of t h e f i r s p e c i e s they i n f e c t
(table 1).
Table 1--The s p e c i e s of dwarf m i s t l e t o e t h a t
i n f e c t t r u e firs
1
MISTLETOE
WHITE FIR DWARF MISTLETOE
l!kmmmu ABEIMM
F , SP.
HOSTS
WHITE FIR, GRAND FIR
*PACIFIC SILVER FIR
RED FIR DWARF MISTLETOE
(Aa ABEIMM F. S p a kWU3Xi)
RED FIR, NOBLE FIR
HEMLOCK DWARF MISTLETOE
*PACIFIC SILVER FIR
*NOBLE FIR
(A- IIlsmu)
* occasional hosts
The white f i r dwarf m i s t l e t o e is p a r a s i t i c
on white f i r s and grand firs,whereas red f i r
and noble f i r a r e t h e p r i n c i p a l h o s t s of t h e
red f i r dwarf m i s t l e t o e . Thus, i n C a l i f o r n i a ,
f o r example, t h e dwarf m i s t l e t o e t h a t i n f e c t s
white f i r w i l l not i n f e c t red f i r and v i c e
versa. Also, seldom do both forms of t h e m i s t l e t o e occur on f i r s where t h e range of two o r more
f i r s p e c i e s overlap. One a d d i t i o n a l f a c t o r t h a t
made t h e f i r - m i s t l e t o e s i t u a t i o n even more confusing i s t h a t f i r s growing i n mixture with
hemlock o f t e n become i n f e c t e d with hemlock
m i s t l e t o e . But t h i s s i t u a t i o n is r e l a t i v e l y
uncommon i n t h e West, and hemlock m i s t l e t o e i s
not considered a major concern i n t h e management
of f i r stands.
Knowledge of t h e host s p e c i f i c i t y of dwarf
m i s t l e t o e s i s of use i n planning harvest c u t s ,
thinning, and regenerating fir stands. The use
of host s p e c i f i c i t y is probably the only method
of s i l v i c u l t u r a l l y managing f o r dwarf m i s t l e t o e
control t h a t can be used f o r both even-aged and
uneven-aged stand s i t u a t i o n s . The following
examples of information useful f o r dwarf mistlet o e control apply only t o even-agedstand management.
t o o l f o r stand regeneration. Most p l a n t a t i o n
t r e e s and n a t u r a l regeneration t h a t a r e 2 t o 3
f e e t t a l l a r e considered well established, and
infected overstory o r r e s i d u a l t r e e s t h a t were
l e f t a s a seed source o r f o r shade should a t
t h i s point be cut o r harvested t o avoid i n f e c t ion of regeneration. This knowledge of t h e
r e l a t i o n s h i p of seedling height t o i n f e c t i o n
from surrounding overstory i s p a r t i c u l a r l y usef u l where i n f e s t e d f i t stands a r e t o be regenerated n a t u r a l l y by narrow s t r i p c l e a r c u t ,
seedtree, o r shelterwood methods.
Small F i r s a r e Seldom
Infected i n Infested Stands
Studies have shown t h a t red f i r s l e s s than
3 f e e t i n height a r e seldom infected by dwarf
m i s t l e t o e , even i n t h e presence of abundant
overstory m i s t l e t o e ( f i g . 1) (Scharpf 1969).
Infection r a t e s increase dramatically i n t r e e s
t a l l e r than 3 f e e t , however. Similarly, intens i t y of i n f e c t i o n on small t r e e s was low, but
increased with t r e e s i z e ( f i g . 2 ) . Being able
t o regenerate an a r e a e i t h e r n a t u r a l l y o r a r t i f i c i a l l y u n t i l seedlings a r e 3 f e e t t a l l without f e a r of appreciable i n f e c t i o n from dwarf
mistletoe gives t h e manager a p r a c t i c a l working
0-3
4-6
7-9
Height-Class
Infected F i r s Free From Overstory Infection
and Growing Well i n Height w i l l Outgrow t h e
Spread and Buildup of Dwarf Mistletoe
Results of long-term dwarf m i s t l e t o e
s t u d i e s D r . J. R . Parmeter and I have made,
provide information about t h e biology, spread,
and buildup of dwarf mistletoe i n young f i r
stands t h a t i s important i n developing guidel i n e s f o r control (Scharpf and Parmeter 1967,
Scharpf and Parmeter 1976). We have found,
f o r example, t h a t t h e spread and buildup of
dwarf m i s t l e t o e i n young red and white f i r s i s
10-12
(feet)
0-3
4-6
7-9
Height-Class
Figure 1--Percentage of red fir infected in
each height-class, with 95 percent confi- dence intervals. (Scharpf 1969)
10-12
(feet)
Figure Z--Number of infections per infected
tree in each height-class, with 95 percent confidence intervals. (Scharpf 1969)
inherently q u i t e slow. Also, c e r t a i n f a c t o r s
keep population l e v e l s low and h e l p check t h e
spread of t h e p a r a s i t e . An important f a c t o r
t h a t influences spread and buildup i s t h a t the
generation time of a m i s t l e t o e p l a n t from seed
production t o i n f e c t i o n and development of a
new seed bearing p l a n t is 5 years o r longer.
Furthermore, female dwarf m i s t l e t o e p l a n t s do
not r e g u l a r l y produce f r u i t every year; often
abundant f r u i t is produced only about once
every 3 years. I n addition, t h e percentage
of t h e t o t a l number of seeds dispersed t h a t
cause i n f e c t i o n is q u i t e low. For instance,
not a l l seeds land on s u s c e p t i b l e branches but
o f those t h a t do, we have found t h a t usually
l e s s than 5 percent of them cause i n f e c t i o n .
Thus, t h e long generation time, sporadic seed
production, and low i n f e c t i o n r a t e s r e s u l t i n
a slow r a t e of buildup and spread of t h e parasite.
The physical c h a r a c t e r i s t i c s o r growth
form of f i r s a l s o l i m i t s spread of t h e p a r a s i t e .
The dense p e r s i s t e n t f o l i a g e of t r u e f i r s l i m i t s
both t h e upward a s well a s the l a t e r a l spread
of t h e p a r a s i t e . For example, r e s u l t s from
our long-term s t u d i e s show t h a t average distance
of v e r t i c a l spread of dwarf m i s t l e t o e i n red
f i r s and white f i r s i s about 3 inches o r l e s s
a year. I n addition, most mature seed bearing
p l a n t s on f i r s a r e located within t h e crown of
infected f i r s and not out on branch t i p s . Thus,
l a t e r a l spread of m i s t l e t o e seeds outside t h e
crown t o other t r e e s i s limited. A s a r e s u l t ,
most of the new i n f e c t i o n s t h a t occur develop
i n s i d e t h e t r e e crown and within one o r two
branch whorls of t h e seed bearing m i s t l e t o e
plant.
Consequently, young t r e e s on good s i t e s
and t r e e s t h a t a r e growing an average of about
a f o o t o r -more i n height w i l l "outgrow" t h e
v e r t i c a l spread of dwarf m i s t l e t o e ( f i g . 3 ) .
In addition, i n f e c t i o n s i n t r e e s i n well managed
even-aged stands contribute l i t t l e t o i n f e c t i o n
of adjacent t r e e s . Of course, it must be kept
i n mind t h a t i n f e c t i o n l e v e l s w i l l buildup i n
t r e e s on poor s i t e s , i n suppressed t r e e s , i n
overstocked stands o r i n young t r e e s exposed
t o heavily infected overstory.
Mortality and Growth Impact From Dwarf
Mistletoe i n Young Managed Stands i s Often Low
Recent unpublished s t u d i e s by Scharpf on
i n f e s t e d released red f i r stands i n California
i n d i c a t e t h a t both m o r t a l i t y and growth impact
Light
Light
Heavy
-40 feet
Infection ratingHeavy
--
2
-2
At t i m e of release
After 20 years
A f t e r 40 y e a r s
A f t e r 60 y e a r s
Figure 3--Rate o f v e r t i c a l spread of dwarf m i s t l e t o e i s l e s s than t h e height growth for t h i s
released red f i r (a hypothetical model).
i n i n f e c t e d t r e e s i s low and within c u r r e n t l y
acceptable management l e v e l s . Five years of
study have shown t h a t no m o r t a l i t y could be
a t t r i b u t e d t o dwarf m i s t l e t o e i r r e s p e c t i v e of
l e v e l of i n f e c t i o n i n any of s e v e r a l released
red f i r stands investigated. Where m o r t a l i t y
from dwarf m i s t l e t o e does become a problem, a s
i n d i c a t e d by a recent USFS p e s t damage inventory,
i s when t r e e s i n i n f e c t e d stands a r e k i l l e d by
a combination of two o r more f a c t o r s , such a s ,
dwarf m i s t l e t o e , f i r engraver b e e t l e , Tomes
annosus and Armillaria mellea (Byler 1975).
Mortality from p e s t complexes i s a l s o higher
than normal i n dwarf m i s t l e t o e i n f e s t e d stands
during periods of prolonged drought (Forest
I n s e c t and Disease Management S t a f f 1977). The
canker fungus Cytospora a l s o causes branch
flagging and some top k i l l i n f i r s weakened by
both moisture s t r e s s and dwarf m i s t l e t o e
(Scharpf and Bynum 1975). However, well r e leased, vigorous f i r stands with dwarf m i s t l e t o e have not shown above normal m o r t a l i t y on
our t e s t p l o t s , even during t h e severe drought
of 1976-77. Therefore, I question whether
dwarf m i s t l e t o e caused m o r t a l i t y w i l l be a major
problem i n well managed stands, even i n combinat i o n with o t h e r p e s t s o r during periods of
adverse c l i m a t i c conditions.
Dwarf m i s t l e t o e a f f e c t s t h e r a d i a l and
height growth of red f i r s . But t h i s e f f e c t
may not be a s severe a s growth l o s s from
suppression and o t h e r f a c t o r s i n unmanaged
stands. Therefore, before dwarf m i s t l e t o e cont r o l i s undertaken i n young o r second-growth
f i r s , t h e stands should f i r s t be brought under
s i l v i c u l t u r a l mangement; t h a t i s , increasing
t r e e vigor commensurate with proper stocking
l e v e l s and o t h e r management considerations.
Release c u t t i n g i n mixed s i z e and age c l a s s e s ,
thinning overstocked stands, brush control and
possibly f e r t i l i z a t i o n a r e examples of p o s s i b l e
management approaches t o increase vigor. Increased vigor automatically r e s u l t s i n increased
height and r a d i a l growth r a t e s and reduction i n
t h e i n t e n s i t y of dwarf m i s t l e t o e . Any attempt
t o control dwarf m i s t l e t o e i n unmanaged stands
i s not aimed a t t h e h e a r t of t h e problem and
w i l l r e s u l t i n wasted resources and e f f o r t .
In t h e management plan,how and when should
dwarf m i s t l e t o e be controlled? To begin with,
control i n i t i a l l y need n o t be considered a s a
separate operation. A good deal of c o n t r o l w i l l
take place i n t h e process of bringing stands
i n t o a well managed condition. For example,
Gordon (1973) reported t h a t noninfected young
f i r s i n California responded well t o r e l e a s e
c u t t i n g by increasing i n height and r a d i a l
growth. I obtained s i m i l a r r e s u l t s i n my s t u d i e s
of both dwarf m i s t l e t o e infected and noninfected
red f i r s . Radial growth r a t e e s s e n t i a l l y doubled
within 10 years a f t e r r e l e a s e f o r both infected
and noninf ected t r e e s ( f i g . 4 ) . Live crown
r a t i o was an important f a c t o r i n t h e subsequent
r a d i a l growth of released t r e e s ( f i g . 5). SO
long a s t r e e s , both infected andnonintectedhad
a good l i v e crown r a t i o , growth increased
markedly a f t e r r e l e a s e .
The e f f e c t of r e l e a s e on height growth of
t r e e s was not investigated i n d e t a i l , however,
from f i e l d observations, I f e e l t h a t height
growth of infected and noninfected red f i r s a l s o
increases markedly a f t e r r e l e a s e . A t any r a t e ,
height growth of study t r e e s , even heavily
infected ones, averaged more than a f o o t a year
within 5 t o 10 years following r e l e a s e ( f i g . 6 ) .
2 Figure
4--Radial growth r a t e of
red fir with various rated l e v e l s
-.
=
2
-0
,
11
None
Light
Medium
Infection rating
Heavy
o f dwarf m i s t l e t o e "before and
a f t e r release w i t h 95 percent
confidence i n t e r v a l s .
5
s
Â
"
4
IP
M
-
Figure 5 - R a d i a l growth of red f i r s
.-m
a f t e r release i n r e l a t i o n t o l i v e
crown r a t i o and dwarf m i s t l e t o e
rating (10 years a f t e r r e l e a s e ) .
-0
m
L
-
-m 3
c
c (0
t-
4 1 ~ 6 0 %live c r o w n
Â
2 1 ~ 4 0 %live c r o w n
2-
m 1
None
-125
I
J
Medium
Heavy
I
Light
Infection rating
+
_c
Figure 6--Mean o f l a s t 5 years o f
height growth o f released red
f i r s i n r e l a t i o n to i n t e n s i t y
o f i n f e c t i o n by dwarf m i s t l e t o e w i t h 95 percent cmf'idence
intervals.
.-M
al
,
o L
m
al
>,
in
Z
m
+
0
ti
c m a
5
None
I
I
J
Light
Medium
Heavy
Dwarf mistletoe rating
The maintenance of good height growth means t h a t
(1) over time, t h e p a r a s i t e w i l l be limited t o
t h e lower p o r t i o n of t h e crown, (2) dwarf
m i s t l e t o e i n t e n s i t y w i l l diminish over time,and
(3) any growth reduction caused by the p a r a s i t e
w i l l become l e s s and l e s s severe i n t h e developing stand. Of course, i n r e l e a s i n g t r e e s o r
i n thinning operations,the manager has the
option of f u r t h e r reducing impact from dwarf
m i s t l e t o e by leaving t h e l e s s severely infected
t r e e s a s crop t r e e s , a s long a s they have l i v e
crown r a t i o s equal t o o r g r e a t e r than t h e inf e s t e d ones. Management of i n f e s t e d t r u e f i r
stands f o r timber production i n t h e s i t u a t i o n
I j u s t described I f e e l w i l l r e q u i r e no additional efforts, a t least f o r the f i r s t rotation,
t o control dwarf m i s t l e t o e even though some
volume l o s s may occur from dwarf m i s t l e t o e
i n f e c t i o n . Attempts a t more complete control
of t h e p a r a s i t e should be considered i n the
f i n a l harvest and i n t h e planning of t h e next
generation f o r e s t .
One of t h e questions o f t e n asked by
managers i s : Won't dwarf m i s t l e t o e trunk i n f e c t i o n s i n young f i r s develop i n t o the l a r g e ,
open, decayed bole swellings commonly observed
on older t r e e s i n infested stands? My observ
t i o n s and unpublished r e s u l t s by D r . Panneter-37
suggest t h a t t h e l a r g e dwarf mistletoe trunk
swellings commonly found on old-growth t r e e s
w i l l not develop and become a problem i n t h e
management of dwarf mistletoe infested, secondgrowth stands. The c u l l and degrade commonly
associated with l a r g e r bole i n f e c t i o n s on oldgrowth f i r s w i l l almost c e r t a i n l y n o t be a
problem i n well managed, s h o r t r o t a t i o n , secondgrowth stands. I n addition, recent s t u d i e s I
have completed have shown t h a t dwarf m i s t l e t o e
does not increase trunk t a p e r i n red f i r s a s
i s o f t e n t h e case with heavily i n f e s t e d pines
and some o t h e r species (Scharpf 1977). Thus,
volume l o s s e s from increased t r e e t a p e r is not
expected t o be a problem i n infested, secondgrowth f i r stands i n t h e West.
One problem involving dwarf m i s t l e t o e i n
young s t a n d s t h a t has not been f u l l y i n v e s t i gated i s t h e a s s o c i a t i o n between dwarf m i s t l e t o e
and t h e canker fungus Cytopsora a b i e t i s . This
fungus a t t a c k s and k i l l s many branches infected
by dwarf mistletoe. I t could k i l l enough of
t h e l i v e crown i n infected t r e e s so t h a t t r e e
vigor and growth r a t e would be markedly decreased. Further s t u d i e s t o provide answers
t o t h i s problem a r e i n progress.
CONCLUSIONS
Control of dwarf m i s t l e t o e i n t r u e f i r s
i n t h e West shows promise because of t h e
v a r i e t y of management options,other than c l e a r cuttingoopen t o f o r e s t managers. The primary
consideration should be t o g e t i n f e s t e d f i r
s t a n d s under good s i l v i c u l t u r a l management
i r r e s p e c t i v e of t h e dwarf m i s t l e t o e s i t u a t i o n .
Good management should r e s u l t i n increased t r e e
growth and vigor--and t h i s w i l l i n i t s e l f r e duce t h e impact of and problems caused by dwarf
m i s t l e t o e and associated p e s t complexes.
E f f o r t s t o control t h e p a r a s i t e i n t r u e f i r s
can be b u i l t i n t o and implemented a s p a r t of
t h e management plan f o r t h e stand. Development
of t h e management p l a n should be based not only
on timber management goals and t h e s i l v i c a l
c h a r a c t e r i s t i c s of t h e stand, but a l s o on t h e
biology and epidemiology of t h e p a r a s i t e . For
t-hft. ?rn b a c C n~lA.t-'LfiLt~~,,
"yich. y,a~nAna
"c'ylMi~'i.'s,
understanding of parasite-host s p e c i f i c i t y , t h e
age o r s i z e a t which young t r e e s become infected,
t h e r a t e s of growth required f o r f i r s t o "grow
away" from spread and buildup of t h e p a r a s i t e ,
and t h e projected impact i n r e l a t i o n t o t r e e
growth r a t e s and dwarf m i s t l e t o e i n t e n s i t y .
Armed with t h i s information, t h e f o r e s t manager
should be a b l e t o make management decisions t h a t
w i l l be s i l v i c u l t u r a l l y sound and e f f e c t i v e i n
t h e control of dwarf m i s t l e t o e i n t r u e f i r stands
i n t h e west. As more information from research
becomes a v a i l a b l e and a s management of f i r stands
become more i n t e n s i v e , f u r t h e r refinement of
control e f f o r t s t o climate l o s s e s from dwarf
m i s t l e t o e can be achieved.
?'verbal communication from J . R. Parmeter, J r . ,
Department of Plant Pathology, University of
C a l i f o r n i a , Berkeley, February, 1978.
LITERATURE CITED
Anonymous.
1972. Forest S t a t i s t i c s f o r t h e United S t a t e s ,
by s t a t e and region, 1970. 96 p. Forest
Service, U.S. Dep. Agric., Washington, D.C.
Byler, James W.
1975. Pest damage inventory
Proceeding of
j o i n t meeting of western f o r e s t i n s e c t work
conference and western i n t e r n a t i o n a l f o r e s t
disease work conference. p. 30-35.
C a l i f o r n i a Forest Pest Control Action Council
1961. Forest p e s t conditions i n C a l i f o r n i a .
Sacramento, C a l i f . p. 12
Forest I n s e c t and Disease Management S t a f f
1977. 1976 and 1977 drought/pest caused t r e e
m o r t a l i t y i n national f o r e s t s of northern
C a l i f o r n i a . C a l i f . Reg. Forest Serv., U.S.
Dep. Agric., San Francisco, C a l i f . 8 p.
Gordon, Donald T.
1973. Released advance reproduction of white
and red fir--growth,damage, m o r t a l i t y . USDA
Forest Serv. Res. Paper PSW-95. 12 p . , i l l u s .
P a c i f i c Southwest Forest and Range Exp Stn.,
Berkeley, C a l i f .
Hawksworth, Frank G . , and Delbert Wiens
1972. Biology and c l a s s i f i c a t i o n of dwarf
m i s t l e t o e s (Arceuthobiwn).U.S. Dep. Agric.,
Agric. Handb. 401, 234 p. i l l u s .
Parmeter, J. R. Jr., and R. F. Scharpf
1963. Dwarf m i s t l e t o e on red f i r and white
i n C a l i f o r n i a . J. For. 61(5):371-374.
Scharpf, Robert F.
1969. Dwarf m i s t l e t o e on red f i r - - i n f e c t i o n
and control i n understory stands. USDA
Forest Serv. Res. Paper PSW-50, 8 p. i l l u s .
P a c i f i c Southwest Forst and Range Exp. S t n . ,
Berkeley, C a l i f .
Scharpf, Robert F.
1977. Dwarf m i s t l e t o e does not increase trunk
t a p e r i n released red f i r s i n California.
USDA Forest Serv. Res. Note PSW-326, 3 p.
P a c i f i c Southwest Forest and Range Exp. S t n . ,
Berkeley, C a l i f .
Scharpf, Robert F. and H. H. Bynum
1975. Cytospora canker o f t r u e f i r s . U.S.
Dep. Agric., Forest Pest Leaflet 146, 5 p.
illus.
Scharpf, Robert F.,and J. R. Parmeter Jr.
1967. The biology and pathology of dwarfm i s t l e t o e , Arceuthobiwn campylopodurn f .
a b i e t i n m p a r a s i t i z i n g t r u e f i r s (Abies
spp.) i n C a l i f o r n i a . U.S. Dep. Agric.
Tech. Bull. 1362, 42 p. i l l u s .
Scharpf, Robert F., and J. R. Parmeter Jr.
1976. Population buildup and v e r t i c a l spread
of dwarf m i s t l e t o e on young red and white
f i r s i n California. USDA Forest Serv. Res.
Paper PSW-122, 9 p. P a c i f i c Southwest Forest
and Range Exp. Stn., Berkeley, C a l i f .
PRESCRIBED FIRE
-
A TOOL FOR
THE CONTROL OF DWARF MISTLETOE I N LODGEPOLE PINE-I /
s.
J. Muraro-21
T h i s paper d e a l s w i t h t h e a p p l i c a t i o n of
f i r e management p r i n c i p l e s t o s a t i s f y l a n d
management n e e d s . What i s f i r e management?
B r i e f l y , f i r e management is t h e a p p l i c a t i o n of
f i r e r e l a t e d knowledge t o a c h i e v e s p e c i f i c
l a n d management o b j e c t i v e s . I n t h i s c a s e ,
t h e r e q u i r e d f i r e r e l a t e d knowledge i s mainly
e c o l o g i c a l and f u e l - w e a t h e r - f i r e b e h a v i o u r
r e l a t i o n s h i p s . The o v e r a l l l a n d management
objective is t o e s t a b l i s h healthy, optimally
s t o c k e d s t a n d s t o maximize f i b e r p r o d u c t i o n .
On a r e a s i n f e s t e d w i t h l o d g-e p
dwarf
- ole pine
m i s t l e t o e (Arceuthobium americanum) Nut t
e x Engelm., t h e t r e a t m e n t t h e r e f o r e h a s two
s p e c i f i c o b j e c t i v e s : s a n i t a t i o n and s t a n d
establishment.
.
I t i s n o t t h e i n t e n t of t h i s paper t o
d i s c u s s t h e p r o s , cons o r economics of m i s t l e t o e c o n t r o l b u t t o s u g g e s t some t e c h n i q u e s
a f t e r t h e p o l i t i c i n g and d e c i s i o n making h a s
been done. I am presuming t h a t t h e l a n d
manager h a s d e c i d e d t o i n s t i t u t e a p o l i c y of
mistletoe control o r a t l e a s t is evaluating
t h e c o s t s of v a r i o u s t r e a t m e n t s s u b j e c t t o
s e l e c t i n g a treatment. Prescribed f i r e ,
p r e v i o u s l y s u g g e s t e d by a number o f r e s e a r c h e r s
(Baranyay and Smith 1972, Donoghue and Johnson
1975, G o t t f r i e d and Emby 1977, K i i l 1969, and
o t h e r s l i s t e d by Alexander and Hawksworth 1 9 7 5 ) ,
is m e r e l y one o f a number of t o o l s which
may b e a p p r o p r i a t e t o t h e j o b . I n t h e c a s e
of l o d g e p o l e p i n e ( P i n u s c o n t o r t a v a r . l a t i f o l i a
Engelm.), which i s r e l a t i v e l y e a s y t o k i l l ,
and h a s a p e r p e t u a l and r e a d y s u p p l y of s e e d
held i n serotinous cones, f i r e has t o be a
strong candidate. I f burning conditions a r e
r i g h t , t h e r e i s no c h e a p e r way t o cover an
a r e a t h a n w i t h f i r e ; however, t h e r e may b e
à ‘ ~ r e s e n t e a t t h e Symposium on D w a r f M i s t l e t o e
C o n t r o l Through F o r e s t Management, Berkeley,
C a l i f . A p r i l 11-13, 1978.
Research S c i e n t i s t , Canadian F o r e s t r y
S e r v i c e , P a c i f i c F o r e s t Research C e n t r e , 506
West B u m s i d e Rd., V i c t o r i a , B.C.
e i t h e r environmental o r p o l i t i c a l r e s t r a i n t s
o r u n f a v o u r a b l e weather regimes t h a t p r e c l u d e
o p e r a t i o n a l u s e of f i r e .
Keep i n mind, m i s t l e t o e e l i m i n a t i o n i s a n
i n t e r m e d i a t e o b j e c t i v e - t h e end o b j e c t i v e i s
economical f i b e r p r o d u c t i o n . With t h i s i n mind,
c o s t comparisons of v a r i o u s t r e a t m e n t s must
i n c l u d e c o s t s of s t a n d e s t a b l i s h m e n t i f t h e
means of s t a n d e s t a b l i s h m e n t a r e d e s t r o y e d by
the s a n i t i z i n g treatment.
The s p e c i f i c a r e a d i s c u s s e d i n t h i s p a p e r
is a t r i a n g u l a r p o r t i o n of t h e I n t e r i o r p l a t e a u
of B r i t i s h Columbia known a s t h e C h i l c o t i n ,
bounded on t h e e a s t by t h e F r a s e r R i v e r , on
t h e southwest by t h e Coast mountains and on
t h e n o r t h by Highway 16. L a t i t u d e s 5 4 ' ~ and
5 1 O ~and l o n g i t u d e 122OW e n c l o s e t h e n o r t h ,
s o u t h and e a s t s i d e s , r e s p e c t i v e l y . The t e r r a i n
is gently r o l l i n g t o f l a t , ranging i n e l e v a t i o n
from 700 t o 1500 m e t r e s . Major d r a i n a g e s d e e p l y
d i s s e c t t h e p l a t e a u . The dominant f o r e s t c o v e r
on t h e p l a t e a u a r e a s a r e multi-aged, m u l t i l e v e l e d s t a n d s of l o d g e p o l e p i n e , t h e r e s u l t
of e x t e n s i v e low i n t e n s i t y f i r e s o c c u r r i n g a t
20- t o 40-year i n t e r v a l s . Each f i r e , i n t u r n ,
t h i n s t h e s t a n d , p r e p a r e s a s e e d b e d , opens a
v a r y i n g number of s e r o t i n o u s c o n e s and a l l o w s
n o n s e r o t i n o u s cones t o open through i n c r e a s e d
exposure. The opened s t a n d p e r m i t s s u f f i c i e n t
l i g h t t o t h e f o r e s t f l o o r t o permit e s t a b l i s h ment of advanced r e g e n e r a t i o n which, i n t u r n ,
i s i n f e c t e d w i t h dwarf m i s t l e t o e from t h e overs t o r y remnants. Occasional s m a l l a r e a s of
d e n s e r , even-aged s t a n d s , i n d i c a t i n g a r e a s of
h i g h e r f i r e i n t e n s i t i e s a r e s c a t t e r e d througho u t t h e a r e a . These even-aged, denser,more
t y p i c a l l o d g e p o l e p i n e s t a n d s tend t o b e f r e e
of m i s t l e t o e .
In general, these Chilcotin pine stands
r a n k low on t h e spectrum of market v a l u e of
l o d g e p o l e p i n e and b e c a u s e of t h e c o l d , d r y
c l i m a t e (annual p r e c i p i t a t i o n 429 mm ("16.5")
growing s i t e s a r e predominantly poor. Howe v e r , t h e a s s i g n e d s i t e c l a s s b a s e d on h e i g h t a g e r e l a t i o n s h i p of t h e c u r r e n t growth probably
r e f l e c t s t o some e x t e n t t h e predominance of
dwarf m i s t l e t o e . N o t w i t h s t a n d i n g , t h e g e n e r a l l y