Forest insect conditions in central and southern Rocky Mountains, 1960

Historic, archived document

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

Bion Paper No. 56 February 1960
Apo vr-e
1b 22.
past a Forest Insect Conditions In
Central and Southern Rocky Mountains
1960

“U.S. DEPT. CF AGRICULTURE
LIP RARY

MAY 3 ~ 1961

QURRENT SERIAL RzCORDS

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~emy

ROCKY MOUNTAIN FOREST AND RANGE EXPERIMENT STATION
Raymond Price, Director Fort Collins, Colorado ‘ }

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FOREST SERVICE U. S. DEPARTMENT OF AGRICULTURE ¥, es > ,

re ee a ee re ee ee ee LPP

KINDS OF SURVEYS

Detection surveys are the sum of surveillance and an annual systematic
aerial survey. Forests covered by a network of roads are reasonably well
patrolled for incipient outbreaks. Areas receiving little or no forest travel
are covered annually by systematic aerial surveys specifically designed to
discover unusual forest damage.

Biological evaluations determine where an infestation is on the infesta-
tion-trend curve. It includes an analysis of population density and numbers
of the pest insects, abundance and susceptibility of the food supply, and
natural enemies and their probable effectiveness. The precision of the
evaluation depends upon the soundness of the survey data and what is known
about the habits of the insect. Workable techniques have been developed
for sampling densities and predicting trends for the Engelmann spruce
beetle, Black Hills beetle, and spruce budworm. Empirical methods must
be used to evaluate infestations of other insect pests until more is known
about their habits.

An operational survey gathers information the forest manager needs
for control planning in addition to the biological evaluation. Operational
surveys delineate infestation boundaries and determine the area or number
of trees infested and the values at stake. : ,

Control or suppression tactics are often a combination of methods to
fit the situation. Expressed in the simplest terms, the objective of direct
control is to sufficiently curtail the multiplication of the pest population 'so
that natural factors can suppress the following generations. Success of the
operations depends upon an accurate biological evaluation and a well designed
and precisely executed control plan.

Cover photo. --Servicing the helicopter in a meadow within the forest saves.
time and costs of the Engelmann spruce beetle detection survey. The more
inaccessible spruce stands in Colorado and northern New Mexico were
covered by helicopter. It is believed that an annual survey should detect
all outbreaks in their early stages.

O
25
.“FOREST INSECT CONDITIONS IN

CENTRAL AND SOUTHERN ROCKY MOUNTAINS, 1960 x

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Rocky Mountain Forest and Range Experiment Station’ »,

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SSK Forest Service, U.-S.-Department of Agriculture

1 Central headquarters maintained in cooperation with

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Colorado State University, Fort Collins (40: //

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FOREST INSECT CONDITIONS IN
CENTRAL AND SOUTHERN ROCKY MOUNTAINS, 1960

Insects can multiply their numbers many times in one generation
when environmental conditions are favorable. Similarly, insect populations
may decline and eventually collapse when the weather is unfavorable or their
biological enemies outmultiply them. For this reason incipient outbreaks
must be discovered early, identified, and promptly controlled. Declining
infestations must likewise be identified and control withheld if we are to
buy the most with the pest-control dollar.

When a pest insect maintains a high population for several consecutive
years, the area of infestation enlarges, much timber may be lost, and the
cost of suppressing the outbreak increases with each new generation. This
happened in the Engelmann spruce beetle outbreak that started from a
widespread blowdown of spruce in 1939. Before it was stopped in 1952, it
killed 53 billion board feet of spruce and lodgepole pine. From 1953 to
1958, bark beetles, aided by a prolonged drought, killed 1.3 billion board
feet of sawtimber in New Mexico and Arizona. Currently, an aggressive
outbreak of the spruce budworm covers 1, 277,120 acres in southern
Colorado and northern New Mexico.

Spruce budworm outbreak
most extensive on record

Mortality of Douglas-fir and true fir caused by the spruce budworm
(Choristoneura fumiferana (Clem. )) has been moderate to heavy for
several years. The advanced reproduction in the understory is receiving
the heaviest damage.

The area of infestation increased from 1, 052, 840 acres in 1959 to
1, 277, 120 acres in 1960 (table 1). Of more importance than this increase
in acreage is the increased amount of area in the heavier defoliation classes.
Light defoliation indicates that the defoliation is barely visible from the air;
moderate, top one-fourth of the trees are defoliated; heavy, top one-half of
the trees are defoliated and top-killing is in progress; and very heavy, top
three-fourths of the trees are defoliated and tree -killing is in progress.

The forecast made in 1959 that damage in 1960 would be severe

proved to be accurate. This forecast was based upon the abundance of
egg masses deposited by the 1959 flight of moths.

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Table 1. --Areas and degrees of defoliation by spruce budworm, 1960

Area Light Moderate Heavy Very heavy Total
a ------ “Sigieh = Sen Se
Colorado
Pike National Forest 93, 900 30, 190 3, 960 350 128, 400
Rio Grande National Forest 17, 430 18, 920 10, 520 1,560 48, 430
Routt National Forest 2, 300 670 80 0 3, 050
San Isabel National Forest 54, 320 5, 940 280 0 60, 540
San Juan National Forest 108, 510 139, 290 10, 730 0 258, 530
Tierra Amarilla Grant 310 8, 090 2, 000 0 10, 400
Uncompahgre National Forest 6, 500 720 230 0 7,450
New Mexico
Carson National Forest
Forest Service land 47, 040 139, 360 14,720 0 201, 120
Adjacent private land 60, 320 103, 040 18, 880 2, 080 184, 320
Santa Fe National Forest
Forest Service land 156, 800 73, 920 10,720 2, 880 244, 320
Adjacent private land 57, 120 10, 880 0 0 68, 000
Navajo Indian Reservation 24, 800 33, 760 4, 000 (0) 62, 560
Total 629, 350 564, 780 76, 120 6, 870 1, 277, 120

Heavy damage is forecast for 1961. -- A heavy egg mass deposit by the
1960 flight of moths will produce a larval population in 1961 that will cause

severe defoliation in many areas unless natural-control factors intervene.
In some areas of southwestern Colorado, the density was less than in 1959.
A summary of the egg mass densities is as follows:

Location and number
of plots in 1960

Colorado

Pike National Forest (6)

Rio Grande National Forest (12)
San Isabel National Forest (3)
San Juan National Forest (16)

Uncompahgre National Forest (1)

Egg masses per l, 000
square inches of foliage

1959 1960
88.9 44,1
20.1 9.1
-- 10.9
23D 12.0
-- 345)

Location and number Egg masses per 1, 000

of plots in 1960 square inches of foliage

(Continued) (Continued)
New Mexico L959 1960
Carson National Forest
Eastern Division and adjacent lands (11) 49.0 31.4
Western Division and adjacent lands (8) 18.4

Santa Fe National Forest
Western Division and adjacent lands (6) 34.6 30.9

Navajo Indian Reservation (4) -- 3309

Areas with more than 15 egg masses per thousand square inches of
foliage will receive severe defoliation unless unpredictable climatic
factors intervene. The decline in egg mass densities on the San Juan and
Rio Grande National Forests is not sufficient for a collapse of the outbreaks,
but it may be an early sign of one. Egg mass sterility and parasitism
varied from Z percent to 34 percent between the plots, or more than double

that in 1959. This amount is not expected to significantly influence the trend
of the infestation.

Figure 1, --Understory and future crop of white fir and Douglas-fir severely
injured by spruce budworm, Carson National Forest.

Figure 2. --Young Douglas-fir severely defoliated by spruce budworm,
Pike National Forest.

Figure 3. --

A; Newly hatched larvae from
spruce budworm egg mass on
Douglas-fir needle.

B, Full-grown spruce budworm
larva on defoliated Douglas-fir
branch.

C, Spruce budworm pupa on branch
tip.

D, Spruce budworm moth.

Engelmann spruce beetle
epidemics still threaten

The Engelmann spruce beetle (Dendroctonus engelmanni Hopk. ) con-
tinues to be a serious problem in mature and overmature stands of
Engelmann spruce in Colorado and northern New Mexico.

Twenty-seven areas of infestation (more than five infested trees per
group) were found in Colorado. Fifteen of these were within or adjacent to
timber sales. The remaining twelve infestations were the result of beetle
population moving from blowdowns into standing green trees. Two such
areas with considerable windthrow were found on the San Juan National
Forest. The East-Mosca-Cold Creek infestation has nearly 10, 000 infested
trees on 7,000 acres. The East Mountain infestation has more than 6, 000
infested trees on 3, 000 acres.

The outbreak reported last year on the Tierra Amarilla Grant near
Chama, New Mexico, increased in severity. Tree-killing is intense on
8, 000 acres of Engelmann spruce, with no signs of a letup in 1961. This
outbreak originated in logging debris in adjacent areas.

An outbreak with a potential of enveloping extensive areas of spruce was
discovered on the Rio Grande Grant and adjacent Carson National Forest in
New Mexico. A large beetle population had been building up for several years
in logging areas on the Rio Grande Grant. The amount of fresh cull and debris
was not adequate to absorb the 1960 beetle flight. Consequently, the beetles
infested many standing trees on the Grant lands and the adjacent Carson National
Forest. The infestation covers about 10,000 acres, about half of which is on the
Carson National Forest. A large number of beetles will emerge in 1961. Wood-
pecker feeding on the new brood is light to absent. This outbreak has the charac -
teristics and the extensive areas of spruce needed for exploding into a major
outbreak.

Figure 4. --Roadless Engelmann spruce forests such as this one on the Arapaho
National Forest can be viewed from helicopter at close range to discover incipi-
ent outbreak centers of Engelmann spruce beetle and blowdowns that breed

outbreaks.

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SRN ORL" Sag,

Figure 5. --Cull logs and tops of Engelmann spruce left in logging areas pro-
vide ideal conditions for a buildup of epidemic numbers of the Engelmann
spruce beetle. :

Figure 6, --Engelmann spruce beetle brood in the cull logs is evaluated by re-
moving bark samples 6 by 12 inches and counting the number of new beetles.

Black Hills beetle infestations
increase in Colorado and Wyoming,
decline in South Dakota

Infestations of the Black Hills beetle (Dendroctonus ponderosa Hopk. )
have plagued the ponderosa pine on the Front Range of Colorado for many
years. Small epidemic areas appeared again in 1960. The greatest increase
was on the Pike and San Isabel National Forests in Colorado and the Bighorn
National Forest in Wyoming (table 2). The number of infested trees increased
7.5 times on the Blue Mountain and 1.3 times on the Stoll.Mountain areas on
the Pike National Forest. Approximately 4, 800 trees are infested on 9, 000
acres in these two infestations.

Table 2. --Location and acreage of Black Hills beetle infestation by intensity classes as

determined from aerial surveys

: Intensity of infestation 1/
National Forest

and adjacent lands : : : ena Toe Bene

Light : Moderate , Heavy : heavy i total d total

- eee ee ee ee ee ee Acres---+--+-+-+-+--------
Arapaho at 300 5 0 0 375 940
Bighorn 25015 600 1, 700 600 5,615 1,010
Pike 15,700 100 20 0 15, 870 2, 100
Rio Grande 325 0 0 0 325 20
Roosevelt 13, 540 1, 050 50 0 14, 640 21, 930
San Isabel 2, 000 250 25 55 2, 330 120
San Juan 5,700 0 0 0 5,700 35, 780
Total 40, 280 2, 075 1,795 705 44,855 61, 900

1

ay Light, 0.1 to 0.2 tree per acre and up to 5 trees per group; moderate, 0.3 to
0.4 tree per acre and up to 10 trees per group; heavy, 0.5 to 0.8 tree per acre and up
to 20 trees per group; very heavy, 0.94 tree per acre and large groups.

Cy Forest not covered completely in aerial survey.

An evaluation of the density of beetles beneath the bark in July in
four infestations produced the following data and predictions:

Location Living beetles Trend of infestation
(No. per sq. ft.)

Roosevelt National Forest
Boulder District 43 increasing
Estes Park District 51 increasing

San Isabel National Forest
San Carlos District 83 increasing

Black Hills National Forest 18 declining

Extensive maintenance control has been necessary on the Black Hills
National Forest for more than 10 years to prevent outbreaks. An operational
survey of the heaviest infestation areas in September showed a decrease of
7.5 to 1 in the number of infested trees.

Scattered tree-killing continues on 1, 000 acres of ponderosa pine on
the Carson National Forest in northern New Mexico. In 1960, 200 infested
trees were sprayed with a water emulsion of ethylene dibromide. Brood
production has been unusually high, 116 beetles per square foot at the time
of emergence. Only by annual treatment of a relatively small number of
trees has a major outbreak been prevented.

Mountain pine beetle outbreaks
continue in lodgepole and limber pine
stands on the Shoshone National Forest

Tree-killing by the mountain pine beetle (Dendroctonus monticolae
Hopk. ) continued at a high rate in limber pine on two areas. Lodgepole pirie
losses are increasing in the Long Creek and Sheridan Creek drainages and
decreasing in several areas. An estimated 12, 620 trees were killed on
21, 145 acres in 1960.

Beetle populations were high in limber pine and in some lodgepole
pine areas. Results of the biological evaluations and trend of the infestations
on the Shoshone are as follows:

Probable trend Level of

Species and
of infestation tree mortality

location Living beetles
(No. per sq. ft.)

Limber pine:

Rock Creek 64 Increasing High

Pete Miller Park 40 Static or High
increasing

Lodgepole pine:

Marston and

Younts Creeks (ail Static High

Wiggins Fork 12 Static or Moderate
decreasing

Long Creek 63 Increasing High

Sheridan Creek (A) 9 Decreasing Low

Sheridan Creek (B) 61 Increasing High

Douglas -fir beetle
damage increases

Infestations of the Douglas-fir beetle (Dendroctonus pseudotsugae
Hopk. ) increased sharply throughout the Douglas-fir stands in Arizona and

New Mexico. The beetle is epidemic on 225,000 acres. New outbreaks were
discovered on the Kaibab and Apache National Forests and the Fort Apache
Indian Reservation. Losses on the Santa Fe and Coronado National Forests
continued at a high level.

Most of the infestations in Colorado and Wyoming are in the light to
moderate categories. Total area of infestation increased from 7, 440 acres
in 1959 to 10, 390 acres in 1960. Fluctuations in infestation trends have been
especially evident on the San Juan National Forest, where 14,000 acres were
recorded in 1958, only 450 acres in 1959, and 2, 320 acres in 1960. Infesta-
tions increased on the Pike, Roosevelt, and parts of the Shoshone National
Forests and decreased on the San Isabel National Forest.

Brood densities were studied in three infestations to develop informa-
tion on the relationship between densities per square foot and the trend of
infestation. The findings were as follows:

Number of living Trend of
Location beetles per square foot infestation

Fall of 1959 Spring of 1960

Clarks Fork District
Shoshone National Forest 42 10 declining

Wapiti District
Shoshone National Forest 42 31 increasing

South Platte District
Pike National Forest -- 33 increasing

Drought conditions and abundant
thinning slash result in engraver
beetle outbreak in the Black Hills

The Oregon pine engraver (Ips oregoni (Eichh. )) was the cause of
scattered group killing of ponderosa pine in the northern Black Hills in
1960. Large beetle populations developed in an abundance of logging and
thinning slash and attacked standing trees. In logged and thinned areas on
both Federal and private lands, groups of 5 to 30 trees were killed. Much
of the mortality was in vigorous reproduction left after thinning. The
epidemic area has been subject to drought in recent years. A similar but
more devastating outbreak developed in the Black Hills in 1933 and lasted
for 4 years.

Fir engraver
damage continues

Two new infestation centers of the fir engraver (Scolytus ventralis
Lec.) appeared, one on the Kaibab National Forest and the other on the
Carson National Forest. Each covers about 600 acres. The 2-year-old
outbreak on the Lincoln National Forest and Mescalero Indian Reservation
is still active on 25,000 acres. Large trees with high value are being killed.
The outbreak on Sandia Mountains, active for many years, is decreasing,
but tree-killing is still severe on 5, 000 acres.

= JQ) =

Large white fir infested with
fir engraver difficult to spot

Spotting trees infested with fir engraver beetles for control and
evaluating the brood for prediction of infestation trend has been handi-
capped by lack of information about the beetle's pattern of infesting the
stem. While the effort this year was limited to a stem analysis of five
trees (figs. 7 and 8), results are interesting and useful. Only the smallest
tree, 12 inches d.b.h., contained brood below 5 feet. The 17-inch tree con-
tained no brood below 10 feet; the 20-23 inch trees contained no brood below
15 feet. Optimum brood production in the stem started at 40 feet and extended
as high as 70 feet. This means that infestations in large trees cannot be
spotted from the ground until the foliage fades.

Figure 7. --Trees
infested with the
fir engraver were
felled and sampled
at heights of 2 feet,
5 feet, and continuing
at 5-foot intervals
until upper limits of
the infestation were
reached.

Figure 8. --Two 6 x 6-
inch bark samples
(1/2 square foot of
bark surface) were
taken from opposite
sides of the bole at
each sampling height
to obtain brood density
and distribution pat-
terns of the fir
engraver.

-]] -

Activity of western baisam
bark beetle continues

The loss of subalpine fir to the western balsam bark beetle (Dryocoetes
confusus Sw.) continues. About 15,000 acres of subalpine fir in Colorado
were infested in 1960 at moderate intensity; epidemic conditions continue on
the Rio Grande National Forest.

Extensive killing of true fir occurred on 40, 000 acres on the Carson
National Forest in northern New Mexico.

Pine bark beetle damage in
New Mexico and Arizona is low

Little mortality of ponderosa pine throughout Arizona and New Mexico
was caused by the complex of Dendroctonus and Ips beetles. Localized out-
breaks were found on the Lincoln National Forest and the San Carlos Indian
Reservation. Several infested trees in the Lincoln outbreak felled for a stem
analysis showed that the Oregon pine engraver killed the top section of the
stems and that Dendroctonus barberi Hopk. and D. convexifrons entered the
Jow.er sections jimi amnion Wi

Arizona five -spined ips - -
a serious enemy of
second-growth ponderosa pine

An outbreak of the Arizona five-spined ips (Ips lecontei Sw. ) continues
to kill second-growth ponderosa pine, particularly within areas set aside for
summer homes or recreation near Prescott, Arizona. Tree-killing in groups
of 10 trees or more (fig. 9) is also common in timber-producing areas. Total
area infested is approximately 10, 000 acres.

Douglas -fir tussock
moth controlled

A new infestation center of the Douglas-fir tussock moth (Hemerocampa
pseudotsugata McD.) was discovered on San Mateo Mountain in New Mexico
during the aerial detection survey in June. The U.S. Forest Service promptly
sprayed this new center of 3,070 acres as wellas 4,707 acres of old. infesta-
tion in the Sandia Mountains, both areas on the Cibola National Forest. Five
widely separated outbreaks have been suppressed in Forest Service Region 3
since this insect was first discovered in the Southwest in 1957.

Saige

Figure 9. --Tree-killing
caused by Arizona five-
spined ips on Prescott
National Forest, Arizona.

Great Basin tent caterpillar out-
breaks continue in some areas

At the time of the collapse of outbreaks in many areas in 1958, new
centers and areas of infestations developed. The present infestations cover
about 100, 000 acres of aspen in northern New Mexico. A native virus of the
caterpillar, a most important natural-control agent, is present in most
infestation centers. The disease failed to erupt in 1960. The number of
caterpillars killed by the virus and other natural agents was negligible.

The downward trend of infestations in southern Colorado started in
1958 when 131, 000 acres of aspen were defoliated. Infested area dropped
to 44,510 acres in 1959 and to 5, 840 acres in 1960. The epidemic lasted
for about 10 years. The caterpillar killed aspen on a net area of about
6, 000 acres and caused an unknown amount of growth loss.

Pandora moth flight
heavy in southern Wyoming

Numerous adults of the pandora moth (Coloradia pandora Blake)
emerged in July from the infestation discovered in 1959 on 8, 420 acres of
lodgepole pine in the Medicine Bow and Routt National Forests. Spent moths
were present in great numbers on the forest floor in August. Many moths
also flew long distances; they were reported as being attracted to lights in
towns more than 100 miles from the outbreak center.

The egg deposit appeared to be light within the infested area. The
pandora moth has a 2-year cycle, spending the first year in the second in-
star larval stage on twigs. Little feeding is done the first year. If the out-
break continues, heavy feeding will take place in 1961. An evaluation of the
infestation trend can best be made in the spring of 1961.

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Miscellaneous defoli-
ator infestations

A localized outbreak of a sawfly (Neodiprion sp.) on ponderosa pine
continues in the Zuni Mountains in western New Mexico. Since its discovery
in 1949, damage has been limited to an area of 1, 200 acres.

Localized infestations of two unidentified leaf rollers are causing
light damage on 1,500 acres of aspen in northern New Mexico and in
northern Arizona.

A needle miner infestation was found in 3, 000 acres of pine on the
Jemez District, Santa Fe National Forest. The infestation presently is
of little or no economic importance.

Forest insect conditions
in Southwest national
parks and monuments

Insect activity on the national parks and monuments of the Southwest
increased slightly in 1960. The most important insects were engraver
beetles, the Douglas-fir beetle, and the fall webworm.

An outbreak of Ips confusus (Lec.) developed in an area of cabled
pinyon -juniper adjacent to Walnut Canyon National Monument. Beetles
that emerged from this slash killed small groups of pinyon in late summer.
Infestations of this same bark beetle continued at Grand Canyon and Mesa
Verde National Parks. Activity decreased at Canyon de Chelly National
Monument and Big Bend National Park.

The Douglas-fir beetle infestation on the north rim of Grand Canyon
continued to increase in 1960. Infested groups of trees are widely
scattered and inaccessible, making control measures impractical.

Spruce budworm feeding is noticeable on the northrim of Grand
Canyon. This is the first activity since the area was aerially sprayed
with DDT in 1958 (see figs. 4-9).

The fall webworm (Hyphantria cunea Drury) is increasing at
Bandelier, Chaco Canyon, and Aztec Ruins National Monuments.

The walnut caterpillar (Datana sp.) infestations at Carlsbad Caverns
National Park were light. Control was continued against the insect on trees
along the approach road.

Agriculture --- CSU, Ft. Collins 15

”