Evaluation of insect and disease conditions in the North Shore Project analysis area, Lake Tahoe Basin management unit

Historic, Archive Document

Do not assume content reflects current
scientific knowledge, policies, or practices.

aSB763

“NG” aa FOREST PEST MANAGEMENT
Pacific Southwest Region

) Report No. C95-7 3420 a :

LL January 17, 1996
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Evaluation of Insect and Disease Conditions in the Worth Shore project ee)
Analysis Area, Lake “*hoe Basin Management Unit Es Sy Sg A

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John M. Wenz, Entomologist
John Pronos, Plant Pathologist

BACKGROUND

In 1995, the Lake Tahoe Basin Management Unit (LTBMU), initiated preparation of
a Draft Environmental Impact Statement to analyze alternative ways to manage
approximately 8,000 acres on the north shore of Lake Tahoe. The proposed
project area includes lands between the urbanized lakeside zone and the LTBMU
watershed boundary from the Truckee River corridor east to Incline Creek. On
July 18-20, 1995, John Wenz, Entomologist, and John Pronos, Plant Pathologist,
Forest Pest Management (FPM), South Sierra Shared Service Area, conducted an
evaluation over part of the project area. The purpose of the evaluation was to
identify the major insects and pathogens active in the area and provide
relevant insect/pathogen-related information for inclusion in the North Shore
Project (NSP) DEIS.

OBSERVATIONS

Observations were made at 11 locations within the NSP area (see Figure 1- Map;
Table 1- List of Locations). The major insects and pathogens found and their
coniferous hosts are given in Table 2. The following discussion is organized
by specific insect or pathogen. Insect and pathogen biologies are provided in
Appendix 1.

INSECTS: As is generally the case with other areas in the Lake Tahoe Basin,
bark and engraver beetles are the most important insects currently affecting
the vegetation. With the exception of light-to-moderate tent caterpillar
feeding on bitterbrush, no noteworthy defoliator activity was observed.

SOUTH SIERRA SHARED SERVICE AREA
pet A parc USDA Forest Service, Stanislaus National Forest
Of Difference 19777 Greenley Road, Sonora, CA 95370

Bark and Engraver Beetles:

1) Fir Engraver, Scolytus ventralis (Coleoptera: Scolytidae). True fir
mortality, top-kill and branch dieback associated with fir engraver activity
was observed scattered throughout the area in mixed confier and fir stands.
Woodborers, probably the roundheaded fir borer, Tetropium abietis (Coleoptera:
Cerambycidae) and/or the flatheaded fir borer, Melanophila drummondi
(Coleoptera: Buprestidae) were frequently found in the lower bole of fir,
particularly red fir, killed by the fir engraver. Evidence (adult galleries)
of other Scolytus spp. was found in the upper boles and branches of down fir
trees and broken tops. Current top-kill and mortality was scattered throughout
the mixed conifer and fir stands but relatively high levels of fir mortality
and top-kill has occurred in the area over the past 4 to 6 years. Based on
needle retention and bark condition in the top-killed portion of the tree, it
was apparent that many individual fir trees had been attacked and then
re-attacked by subsequent generations of the fir engraver. Fir engraver
attacks that top-kill less than 20 to 30% of the crown do not necessarily
result in death of the entire tree, particularly if the tree is otherwise
healthy. However, if the the initial attack and/or subsequent re-attacks kill
more than about 30% of the crown, the tree is not likely to recover.

Stocking levels in the North Shore mixed conifer and fir stands evidencing fir
mortality were variable frequently ranging from about 270 sq.ft./acre to 360
sq.ft./acre of basal area. Both overstory and understory fir were attacked by
the engravers often in stands where dwarf mistletoe and Cytospora canker were
prevalent. The condition of the host tree can be one factor influencing
successful beetle attack. Trees weakened by predisposing factors such as
diseases, between-tree competition due to overstocking, physical injury and/or
moisture stress, are more likely to be successfully attacked than healthy
trees. Thus, regulation of stocking through vegetation management (including
thinning), in combination with the mitigation of other predisposing factors,
should allow trees to grow as vigorously as possible and reduce chances of
successful bark and/or engraver beetle attack.

2) Mountain Pine Beetle, Dendroctonus ponderosae (Coleoptera:
Scolytidae). Some mountain pine beetle-related mortality was observed in
lodgepole pine stands generally restricted to wet or riparian areas. Mountain
pine beetle was also observed killing scattered, individual, sugar pine.

3) Jeffrey Pine Beetle, D. jeffreyi. Scattered, individual tree and a few
small groups (<10 trees/group) of Jeffrey pine beetle-related Jeffrey pine
mortality were present in the lower elevation pine stands. In general, Jeffrey
pine mortality in the North Shore area appeared less than that which has
occurred over the past several years in East and South Shore areas. Red
turpentine beetle (D. valens) were found in the base of some Jeffrey pine but
at very low levels. Pine engraver (Ips spp.) activity was also very low.

Defoliators:
Light-to-moderate tent caterpillar, Malacosoma sp. (Lepidoptera: Lasiocampidae)

feeding on bitterbrush, Purshia sp. (Rosaceae), was observed in relatively open
areas with numerous host plants. Tent caterpillar populations periodically

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reportedly not caused serious, longterm, adverse effects.

PATHOGENS (generally listed in order of decreasing frequency and potential for
Causing damage)

Dwarf Mistletoes:

Red fir dwarf mistletoe (Arceuthobium abietinum f.sp. maqnificae) was the most
common of these parasites, followed by white fir dwarf mistletoe (A. abietinum
f. sp. concoloris) and very small amounts of lodgepole pine dwarf mistletoe (A.
americanum). No mistletoe was found on Jeffrey pine. The distribution of
dwarf mistletoes at North Shore was typically irregular. Infections at a given
site could vary from none to severe. Most stands of true fir in the project
area were multi-storied, and in some, dwarf mistletoe was present at
significant levels in all age classes of trees. On sites with mistletoe,
normally only one species was infecting a single species of conifer host.

Whenever present, dwarf mistletoe should be considered in the management of
that site. Moderate to heavy infections eventually weaken trees so that they
are more vulnerable to drought stress and insect attack. A variety of
silvicultural treatments can be used to effectively control these parasites.
Lightly infected stands are the easiest to treat and require the least radical
steps. One of the most difficult situations to manage is when dwarf mistletoe
is well established in uneven aged stands. Because of its disperal mechanism,
it is almost impossible to maintain a vigorous overstory and understory when
both are infected.

Annosus Root Disease:

This root disease is caused by the fungus Heterobasidion annosum, and was
repeatedly found affecting true fir in the North Shore area. Pine species were
free of root disease. Every sparsely stocked small opening that had large, old
stumps and evidence of fir mortality occurring over a long period of time had
signs and symptoms of root disease. In most cases the fungus was acting as a
butt rot. It was not causing obvious mortality, except in seedling and sapling
size fir, and it did not appear to have caused much windthrow. Depending on
management objectives, the effects of this root disease can be considered
either desirable or undesirable.

In unmanaged true fir and mixed conifer stands, H. annosum usually exists at
low levels as a natural part of the ecosystem. Entering these stands to
harvest green timber, build roads, establish campgrounds, or salvage dead trees
tends to increase the amount of annosus root disease by creating convenient
entry points (stump tops and wounded trees) for the fungus. Thus, we find this
root pathogen most concentrated on sites where trees have been repeatedly
removed. Pesticides containing borate compounds (borax, Sporax) applied to
stump tops are very effective in preventing the start of new annosus root
disease centers. These materials, however, do not stop the underground spread
of this root disease pathogen once it has become established, nor are they

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effective for treating basal wounds created during harvesting. Improving
logging practices is the best way to prevent tree damage.

Cytospora Canker:

A fungus (Cytospora abietis) causes this disease which can kill small firs and
the branches of larger trees. It is a weak parasite that attacks trees already
stressed by other factors. This organism, in association with dwarf mistletoe,
is responsible for much of the branch "flagging" common in recent years to many
areas in the Sierra Nevada. Branches with dwarf mistletoe are infected by
Cytospora and eventually die. The ultimate effect of this canker is to reduce
the amount of live crown on true fir which may lead to reduced tree vigor and
predisposition to insect attack.

White Pine Blister Rust:

This disease is caused by the non-native fungus Cronartium ribicola, which can
be especially lethal to small 5-needled pines. It was found infecting sugar
pine in two North Shore units and western white pine in a third unit. While
the frequency of this pathogen is not currently high, the amount of sugar and
western white pines in the project area is also rather low. Over the period of
several decades, blister rust can eliminate most seedlings and saplings of
susceptible species, and will continue to kill natural regeneration as it is
produced. This results in stands with only large sugar pines (they may be
infected but not always killed) and no replacements. The best way to ensure
sugar pine seedling survival is to plant trees with genetic resistance to this
disease.

Yellow Witches-Broom:

This is another disease caused by a rust fungus (Melampsorella caryophyllace-
arum that primarily infects white fir in the Sierra Nevada. It produces
conspicuous densely branched witches-brooms with very short yellowish needles.
The effect is mostly cosmetic with little damage to the host tree. The
witches-brooms may be mistaken for dwarf mistletoe infections by those
unfamiliar with this disease.

MANAGEMENT ALTERNATIVES

The following insect and disease management alternatives are not mutually
exclusive. They are intended to be considered for integration into overall
LTBMU vegetation management plans and forest health activities. Several of the
alternatives (e.g., regulation of stocking, regulation of species composition,
sanitation) provide opportunities to reduce undesirable effects of both insects
and pathogens. Combination of the alternatives may be implemented depending on
the insects/pathogens present and location-specific management objectives.

1. No Management. The high levels of insect/pathogen-related mortality
experienced in the North Shore and other areas of the Lake Tahoe Basin over the

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past several years is a consequence of the interactions between weather
(drought), current stand conditions and insects and diseases. If no direct
and/or indirect actions are taken to change or mitigate factors associated with
undesirable insect and pathogen effects, it is likely that relatively high
mortality and top-kill will continue on a fluctuating, periodic, basis. This
may be particularly evident in stands with a high proportion fir due to a
combination of dwarf mistletoe, annosus root disease and fir engraver. Such
mortality increases the amount of standing dead and down woody material which
may affect the need/opportunity for salvage and result in increased dead fuels,
increased wildlife habitat for snag and down woody material dependent species,
increased decomposition and nutrient cycling and, depending on location, the
creation of hazardous trees.

2. Bark/Engraver Beetle Management.

The following management options may be considered for bark and engraver
management: (A) direct suppression; (B) regulation of stocking; (C) regulation
of species composition and D) disease management.

A) DIRECT SUPPRESSION. Direct control of Jeffrey pine beetle through the
removal of infested trees has been circumstantially shown to be effective
in reducing subsequent Jeffrey pine beetle-related mortality in developed
recreation sites in the Lake Tahoe Basin. Efficacy probably increases if
infested trees are removed annually or over several consecutive years.
Under most circumstances in California, direct control has not been shown
to be consistently effective in controlling area-wide populations of other
bark/engraver beetles such that subsequent mortality is reduced to
acceptable levels.

B) REGULATION OF STOCKING. The purpose of stocking control is to thin
overstocked stands and vegetation aggregations to levels appropriate for
the site. From the bark/engraver beetle perspective, the intent is to
create and maintain healthy vigorously growing trees and stands that have
an increased chance of preventing successful attacks. Much of the
bark/engraver beetle-related mortality on the North Shore has occurred in
stands with basal areas ranging from about 270 sq.ft./acre to 360
sq.ft./acre. Work with pine bark beetles from several areas in the west
indicates that reducing stocking to about 55% to 75% of normal basal area
effectively reduces mortality.

C) REGULATION OF SPECIES COMPOSITION. Some of the fir engraver-related
mortality occurred in mixed conifer stands that currently have a relatively
high proportion of fir, primarily white fir. Many of these stands may have
historically had a higher proportion of pine. Increasing the amount of
pine in these stands will, through time, reduce host availability for the
fir engraver and increase species diversity at the stand level. If also
managed for other predisposing factors (e.g., stocking levels, diseases),
bark and engraver beetle-related mortality should be reduced.

D) SANITATION/DISEASE MANAGEMENT. In addition to regulating stocking and
species composition, removal of selected poorly growing, unthrifty trees,
that will not likley respond to thinning should improve overall stand vigor
and reduce the potential for bark/engraver beetle attack. This can include
removing trees with physical injuries, poor needle retention, diseases

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(particularly dwarf mistletoe- see discussion below), live crowns of less
than 20-30% of the tree height, current top-kill of more than 30% of the
live crown, and current branch dieback that affects at least 50% of the
live crown. The decision to remove individual or groups of trees through
thinning and/or sanitation for insect/disease management purposes should be
made within the context of overall resource management goals and objectives
and the desired condition for the area.

3. Dwarf Mistletoe Management. As mentioned above, mistletoe infestations can
be reduced each time a stand is entered for thinning or sanitation purposes.
The steps required for control in a particular area depend on the severity of
infection, which is determined by the distribution of mistletoe within the
stand and how long it has been allowed to build up. Listed below are the most
commonly used approaches for suppression.

A. OVERSTORY REMOVAL. One of the first rules for managing stands with
dwarf mistletoe is to remove infected overstory trees in order to protect
the understory. The only time infections in the overstory are tolerated is
when there is no existing understory of susceptible species or when an
understory of non-host species is to be established (species conversion).
Removing infected trees from the overstory may not fit well when uneven
aged management is a goal. Large trees can be killed and left standing if
their use as wildlife snags is desired.

B. SANITATION THINNING. The most heavily infected trees are removed to
reduce the overall effect of mistletoe, lower the risk of engraver beetle
attacks, and increase the vigor of the residuals. For example, true fir
with Hawksworth ratings of 5 or 6 have only a life expectancy of another
10-15 years, are growing very slowly, and are a major source of infection
for adjacent trees. The overall health of most stands would increase with
the removal of these trees. Released trees on good sites will outgrow the
remaining mistletoe. It is not necessary to eliminate all mistletoe as
long as no overstory source of mistletoe seed is present.

Dwarf mistletoe sanitation will also reduce the amount of Cytospora canker
present in a stand because this canker is so closely linked with mistletoe
infections. Trees with diseases like yellow witches-broom may also be
targeted for removal during sanitation treatments.

C. ELIMINATE STAND AND REGENERATE. This treatment may be the only
effective option for the most severely infected stands where no non-host
species are present. By removing all hosts we eliminate this obligate
parasite and are able to start over with disease-free trees.

D. REGULATE SPECIES COMPOSITION. Because dwarf mistletoes are host
specific, altering the tree species composition in mixed stands can reduce
or eliminate the negative long term impacts of this pest. Standard
silvicultural procedures during normal entries can be used to accomplish
this treatment. Planting also offers an opportunity to establish tree
species resistant to any dwarf mistletoes that are present in adjacent
trees or stands.

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E. PRUNING. Removing the infected portion of a tree’s crown is not
normally economical in the general forest, but is commonly used in
recreation and administrative sites where individual tree value is high.
Selectively removing only witches-brooms from high value trees can increase
tree vigor and prolong the life of these individuals, even though mistletoe
remains in the crown.

F. USE BUFFER ZONES. Any management strategy for dwarf mistletoe should
include steps to prevent the parasite from moving back into treament areas
from adjacent infected trees. Buffer zones can occur naturally or be man
made, and are any areas that do not contain host material susceptible to
the mistletoe(s) present. Examples include: meadows, lakes, rivers,
openings, clearings, roads, and plantings of non-host trees.

Root Disease Management.

A. SANITIZE AREAS AFFECTED BY ROOT DISEASE. Most of the fir within root
disease centers are either already infected or will be in the future. A
challenge with this root pathogen on true fir is that infected trees do not
always show obvious above ground symptoms. This means that identifying
root diseased trees and the boundaries of disease centers may be diffi-
cult. If true fir growth rates or mortality are unacceptable, consider
removing all host trees within disease centers and convert to non-host
species, such as Jeffrey pine and rust resistant sugar pine which presently
are at low levels in most stands. Heterobasidion annosum will remain
active on the site and may still move underground to nearby fir.

A more aggressive approach would be to sanitize the root disease centers
and remove an additional strip of green host trees from the adjacent
healthy stand. The intent here is to cut uninfected trees far enough in
advance of annosus root disease to allow non-parasitic root inhabiting
fungi to invade and colonize root systems. Essentially, this would deny H.
annosum access to these roots, and the enlargement of centers would be
stopped. Based on the size and spacing of fir in most of the North Shore
Area, the buffer zone would have to be 80-100 feet wide. Treating all cut
stumps with Sporax is necessary for the treatment to be effective.

B. SPORAX. This pesticide is effective in keeping annosus root disease
from infecting freshly cut stumps, and therefore prevents the start of new
disease centers. Sporax does not control H. annosum that is already
established in roots. Use of this preventive pesticide is routine in many
pine type situations, especially on the east side of the Sierra crest. Use
of Sporax in true fir is less common, primarily because of the difficulty
in identifying diseased areas and because the pathogen is already
established in so many true fir stands. Still, Sporax will prevent the
start of new disease centers, and its use in the North Shore Project Area
should be considered wherever true fir will remain as a stand component.

On the other hand, if stumps are not treated, the potential for introducing
more root disease is created each time trees are cut. The easiest approach
would be to treat all fir stumps, greater than 12 inches diameter, cut
during harvest. It may be questionable to use Sporax within root disease
centers where annosus is well established. If it is desirable to reduce

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the amount of pesticide used or lower cost, Sporax treatment could be
limited to areas free of root disease.

C. MINIMIZE DAMAGE TO RESIDUAL TREES. The following guidelines are
intended to reduce injury to residual trees and thereby prevent future
losses from wood decay, including annosus root disease. They were
developed by the Pacific Northwest Research Station and the Region 5
Silvicultural Development Unit and should be considered whenever entering
true fir stands.

is est t e of lo - Do not allow entry during the spring and
early summer when tree bark is loose and the likelihood of
mechanical damage is greatest.

2. Restrict the size and type of logging equipment. Match the logging
system to the topography and use the smallest size of equipment to

get the job done. Use cable systems on slopes steeper than 35%.

3. Mark leave trees rather than cut trees. Marking crop trees makes
them easier to see and avoid.

4. Lay out skid roads in advance of logging. Skid trails should not be
cleared wider than the skidding vehicle. Use straight-line skid

trails.

5. Leave buffer (bump) trees. When possible, leave cull logs and bump
trees along the edges of skid trails. Remove bump trees during the

last turn.

6. Limit log length. Relate log length to the spacing of the residual
stand. The longer a log, the more likely it is to damage leave
trees.

7. Log skid trails first. Cut the stumps in skid trails as low as
possible, preferably 3-4 inches high.

8. Use directional falling. Fall trees toward or away from the skid
trails to reduce skidder maneuvering.

9. Limb, top, and buck trees prior to skidding.
10. Do not thin stands of thin-barked trees too heavily. Sunscald after

logging can cause considerable damage to thinned bark trees like
true firs.

11. Work close with contractor. Instruct operators in methods of
reducing damage. Inform contractor that damage will not be
tolerated. Communicate clearly the desired results to the contractor
- close supervision may be necessary, especially with inexperienced
operators.

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5. White Pine Blister Rust Management. Any projects that involve tree
planting create the opportunity to establish sugar pine seedlings that are
genetically resistant to blister rust. This is the best strategy to ensure
that sugar pine remains a component of stands in the Lake Tahoe Basin. Using
non-resistant stock would probably result in survival of less than 10%
(including no survival at all). Also, any activities that would increase the
amount of Ribes sp. in a stand or allow it to invade into a new area would
increase the threat of blister rust.

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10

Table 1. Specific Site Locations for Areas Evaluated During FPM Biological
Evaluation, North Shore Project, July 18-20, 1995.

SITE NUMBER LOCATION
1 R17E T15N S6 Northwest
2 R16E T16N S35 Southeast
3 R16E T16N S35 Northeast
4 R16E T16N S26 Central
5 R16E T16N S26 North-central
6 R17E T16N S1 North-central
7 R17E T16N S10 Northwest
8 R17E T16N S8 East-central
9 R17E T16N S17 Central
10 R16E T16N S24 Southwest

11 R17E T16N S21 West-central

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11

Table 2. Major Insects, Pathogens, and Associated Host Plants, by Site Found
During the North Shore Project Biological Evaluation.

PATHOGENS
Dwarf Mistletoes
Arceuthobium abietinum f.sp. conc

A. abietinum f.sp. magqnificae
A- americanum

Annosus Root Disease

Heterobasidium annosum
Cankers

Cytospora abietis
Rusts

White pine blister rust

Cronartium ribicola

Yellow witches-broom
Melampsorella caryophyllacearum

NSECTS

Bark/Engraver Beetles

Fir engraver beetle

Scolytus ventralis

Mountain pine beetle
Dendroctonus ponderosae

Jeffrey pine beetle
D._jeffreyi

Woodborers

Roundheaded fir borer
Tetropium abietis

Flatheaded fir borer
Melanophila drummondi

Defoliators

Tent caterpillar

Malacasoma sp.

HOST PLANT

White fir
Red fir
Lodgepole pine

White/red fir

White/red fir

Sugar pine
Western white
pine

White fir

White/red fir
Lodgepole pine
Sugar pine

Jeffrey pine

White/red fir

White/red fir

Bitterbrush

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Appendix 1. Insect and Pathogen Biologies

Fir Engraver

The fir engraver (Scolytus ventralis) attacks both white and red fir in
California. Trees ranging in size from large saplings to overmature
sawtimber are susceptible. Attacks can cause patch-killing of cambium
along the bole, top-kill, or tree death. Top-kill or death occur most
often in firs that have been weakened by root disease, dwarf mistletoe,
overstocking, soil compaction, sunscald, logging injury, or drought. The
fir engraver also breeds in slash and windthrown trees.

The fir engraver usually completes its life cycle in one year, sometimes
two. Adults fly and bore into trees or green fir slash from June to
September; larvae, pupae, and adults over-winter under the bark. Pitch
tubes are not formed as they are with pine bark beetles; the usual
evidence of attack is boring dust in bark crevices along the trunk and
pitch streamers on the mid and upper bole. Trees colonized early in the
summer may begin to fade by early fall, but those colonized later in the
year usually do not fade until the following spring or summer, often after
the beetles have emerged.

Mountain Pine Beetle

The mountain pine beetle, Dendroctonus ponderosae, attacks the bole of
ponderosa, lodgepole, sugar and western white pines larger than about 4 inches
dbh. Extensive infestations have occurred in mature lodgepole pine forests.
Group killing often occurs in mature forests and young overstocked stands of
ponderosa, sugar and western white pines.

The life cycle of the mountain pine beetle varies considerably over its range.
One generation per year is the general rule, with attacks occurring from late
June through August. Two generations per year may develop in low elevation
sugar pine.

Attacks may extend from the root collar up to near the top. Pheromones released
during a successful attack may attract enough beetles to result in a group
kill. Pitch tubes and red boring dust in bark crevices or on the ground
indicate successful attacks.

The adults bore long vertical egg galleries and lay eggs in niches along the
sides of the gallery. A "J"-hook is common at the lower end of the gallery.
The hatching larvae feed in mines perpendicular to the main gallery and

construct small pupal cells at the end of these mines where they pupate and

transform into adults.

The sapwood of successfully attacked trees soon becomes heavily bluestained.
The bluestain fungi probably aid in overcoming the defenses of the host tree.

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14

Natural factors affecting the abundance of the mountain pine beetle include low
winter temperatures, nematodes, woodpeckers and predaceous and parasitic
insects. As stand susceptibility to the beetle increases because of age,
overstocking, diseases or drought, the effectiveness of natural control
decreases snd mortality increases. Relieving stress by thinning dense stands
can prevent some group kills. Individual high value trees undergoing temporary
reversible stress may be protected from attack by application of insecticide to
the bole.

Jeffrey Pine Beetle

The Jeffrey pine beetle (JPB) is the principle bark beetle found attacking
Jeffrey pine, Pinus jeffreyi, which is its only host. It is a native insect
occurring throughout the range of Jeffrey pine from southwestern Oregon
southward through California and western Nevada to northern Mexico. The beetle
normally breeds in large, slow-growing, mature and/or stressed trees and under
such conditions, mortality usually occurs as scattered, individual trees as
opposed to large groups. Under outbreak conditons, often triggered by drought
or other factors that weaken trees and predispose them to JPB attack, pines
with diameters >6 inches DBH are attacked. Mortality under these conditons
often occurs in large groups of from 30 to 100 or more trees. The JPB is not
known to successfully breed in slash.

The JPB usually completes one generation per year in the northern part of its
range but may complete two generations in the south. The adults generally fly
and attack between late-May/early-June and early-October. The adults are
cylindrical, reddish-brown to black, and are about 5/16 inch in length. Upon
successfully attacking a Jeffrey pine, usually in the mid to lower bole, the
adult JPB excavate a longitudinal egg gallery in the cambium/inner bark that
often has a distinctive "J" shaped segment at the bottom. The eggs are laid in
niches along the sides of the egg gallery which is packed with frass. After
hatch, the larvae feed in mines perpendicular to the egg gallery and end in
open, oval-shaped pupal cells in which pupation occurs. The JPB tends to
overwinter as larvae and adults.

Jeffrey pine attacked by JPB can be identified by reddish pitch tubes on the
bole where adults have attacked and/or brownish to reddish frass (boring dust)
that collects in bark crevices and at the base of the tree. Attacked trees
also exhibit a sequence of crown fade from greenish yellow to reddish brown.
Frequently, crowns do not begin to fade until the spring of the year following
attack.

Several other organisms are often associated with the attack of the Jeffrey
pine beetle. Bluestain fungi, yeasts, and other fungi are transferred into the
tree by the attacking adults. The California flatheaded borer, Melanophila
californica, the pine engraver, Ips pini, and the emarginate ips, I.
emarginatus, may be found in JPB attacked trees.

Red Fir Dwarf Mistletoe

Red fir dwarf mistletoe, Arceuthobium abietinum f. sp. magnificae, is a
seed-bearing plant that parasitizes only red fir. It will not survive without

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living host tissue, which it depends on for support, food, nutrients, and
water.

Dwarf mistletoes initiate their life cycle when a seed lands on a needle or
small twig of a host. The seed is coated with viscin, a sticky substance that
allows it to adhere to the host tissue. During rains, the viscin becomes
mucilaginous, allowing the seed to slide down to the needle base where it may
lodge. The seed germinates in the winter or spring and the radicle grows along
the twig until it reaches a needle base or bark irregularity. The radicle
forms a holdfast and penetrates the twig into the xylem. A type of root system
then develops in the twig. In 3 to 5 years from seed deposition, most
successful infections will appear as branch swellings and will bear mistletoe
shoots. These shoots will not produce fruit until at least 5 years following
seed deposition, the average being 8-9 years. Fruit mature in the fall and
disseminate seed in September and October. The seeds are explosively
discharged from the fruit through the buildup of turgor pressure. Seeds
normally have an upward trajectory.

Red fir dwarf mistletoe does not spread rapidly following establishment.
Vertical spread in a tree averages less than 3 inches per year. Horizontal
spread in a stand without overstory infection is also quite limited. The dense
foliage of red fir limits spread because of the high probability of
interception of the seed. Spread from infected overstory to understory may be
up to about 100 feet, but it is usually less; the actual distance is dependent
on slope, wind, and other factors. Trees less than 3 feet tall have a very
limited chance of infection because of their small target size.

The effects of this mistletoe on true fir growth and mortality relative to the
Hawksworth 6-Class rating system are shown below. Source: Hawksworth, F.G.,
et. al., 1992. Interim dwarf mistletoe impact modeling system - users guide
and reference manual. USDA Forest Service, Forest Pest Manangement, Methods
Application Group, Fort Collins, CO, Report MAG-91-3, 90p.

0 1 2 3 4 5 6
10-YEAR GROWTH LOSS (%): 0 .e) O 2 5 30 50
10-YEAR MORTALITY (%): 0.0 0.7 2.3 5.0 8.8 13.5 19.2

Annosus Root Disease In True Fir

Heterobasidion annosum (formerly Fomes annosus) is a fungus that attacks a
wide variety of woody plants. All western conifer species are suscept-
ible. Madrone and a few brush species (Arctostaphylos spp. and Artemisia
tridentata) are occasional hosts. Other hardwood species are apparently
not infected. The disease has been reported on all the National Forests

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in California, with incidence particularly high on true fir in northern
California campgrounds. Incidence is somewhat higher in older, larger fir
stands and in stands with high basal areas (over about 330 square
feet/acre).

During periods favorable to the fungus, fruiting bodies (conks) form in
decayed stumps, under the bark of dead trees, or under the duff at the
root collar. New infection centers begin by aerial spread of spores
produced by the conks and subsequent colonization of freshly cut stump
surfaces or wounds on living trees. The fungus then spreads through root
contacts into the root systems of adjacent live true fir. Local spread of
the fungus from a stump typically results in the formation of a disease
center, with dead trees in the center and fading trees on the margin.
These centers usually continue to enlarge until they reach natural
barriers such as stand openings or non-susceptible plants.

In pines, H. annosum grows through root cambial tissue to the root crown
where it girdles and kills the trees. In less resinous species such as
true firs, the fungus sometimes kills trees, but more frequently it is
confined to the heartwood and inner sapwood of the larger roots where it
causes a chronic butt and root decay and growth loss. Thus, while
infection in true fir usually does not kill the host, it does affect its
growth and thriftiness. Losses in true fir from H. annosum are mainly the
result of windthrow because of root decay, and reduced root systems that
predispose trees to attack and eventual death by the fir engraver beetle.
Field observations suggest that vigorous young firs are usually able to
regenerate root tissues faster than they are lost to the root disease.

But when true firs slow in growth because of stand and/or site conditions,
root development decreases to where there is a net loss in roots and the
trees slowly decline due to the gradual loss of their root systems. This
decline may take 10 to 20 years before tree death occurs.

There are two pathogenic strains of the fungus that differ in their
ability to infect various conifers in California. The "P" or pine type
infects and kills all pines (although susceptibility of pine species
vary), in addition to incense-cedar and western juniper. The "S" or fir
type infects true fir, Douglas fir and giant sequoia. Knowing which type
is active in a stand is important, and will allow favoring alternate
conifer species because the fungus strains do not cross infect between the
two groups listed above.

Cytospora Canker

Cytospora abietis is a canker-causing fungus that infects true firs
throughout their range in California. It is a weak parasite, and usually
attacks trees that have been weakened by disease, drought, fire, insects,
or human disturbance. It is most commonly associated with dwarf mistletoe
infection, and sometimes attacks as many as a quarter of the
mistletoe-bearing branches, killing many each year. The bright red flags
of recently-killed branches on dwarf mistletoe-infected red firs are
almost always the result of lethal Cytospora infections. C. abietis
occasionally reaches especially damaging proportions in certain years, and

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trees.

t ne Blister Rust

Blister rust (Cronartium ribicola) is caused by an obligate parasite that
attacks sugar and western white pines and several species of Ribes. The fungus
needs the two alternate hosts to survive, spending part of its life on
5-needled pines and the other on Ribes. The disease occurs throughout the
range of sugar pine to the southern Sierra Nevada, but has not been reported
further south. Infection of pines results in cankers on branches and main
stems, branch mortality, top kill, and tree mortality.

Spores (aeciospores) produced by the fungus in the spring on pine bole or
branch cankers are wind-disseminated to Ribes where they infect the leaves.
Spores (urediospores) produced in orange pustules on the underside of the
leaves re-infect other Ribes throughout the summer, resulting in an
intensification of the rust. A telial spore stage forms on Ribes leaves in the
fall. Teliospores germinate in place to produce spores (sporida) which are
wind-disseminated to pines and infect current year needles. Following
infection, the fungus grows from the needle into the branch and forms a
canker. After 2 or 3 years, spores are produced on the cankers and are spread
to Ribes to continue the cycle. Although blister rust may spread hundreds of
miles from pines to Ribes, its spread from Ribes back to pines is usually
limited to a few hundred feet.

Branch cankers continue to enlarge as the fungus invades additional tissues and
moves toward the bole. Branch cankers within 24 inches of the bole will
eventually form bole cankers (these are called lethal cankers). Bole cankers
result in girdling and death of the tree above the canker. Cankers whose
closest margins are more than 24 inches from the main bole are unlikely to
reach the bole and only branch flagging will result (these are called non-
lethal cankers).

Environmental conditions are critical for successful infection and limit the
disease in most years. Moisture and low temperatures favor infection of both
hosts, and must coincide with spore dispersal for infection to occur. In
California, these conditions occur only infrequently, usually in cool moist
sites such as stream bottoms or around meadows. In so called "wave years" when
favorable conditions occur, high levels of infection can result. Wave years in
California have occurred at approximately ten-year intervals in the past. As
one moves from sites most favorable for rust to less favorable sites, the
frequency of wave years decreases.

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