Effects of lnsecticide Treatments on

Subsequent Defoliation by Western

Spruce Budworm in Oregon and

Washington: 1982-92

Katharine A. Sheehan

United States

Department of

Agriculture

Forest Service

Pacific Northwest

Research Station

General Technical

Report

PNW-GTR-367

March 1996
KATHARlNE A. SHEEHAN is an entomologist, U.S. Department of Agriculture,

Forest Service, Pacific Northwest Region, Natural Resources, P.O. Box 3623,

Portland, OR 97208-3623. This work is the result of cooperation between the Pacific

Northwest Region and the Research Station.

Author

This publication reports analyses involving pesticides. It does not contain recommendations for their use, nor does it imply that the uses discussed here have been

registered. All uses of pesticides must be registered by appropriate State and

Federal agencies before they can be recommended.

CAUTION: Pesticides can be injurious to humans, domestic animals, desirable

plants, and fish or other wildlife—if they are not handled or applied properly. Use all

pesticides selectively and carefully. Follow recommended practices for the disposal

of surplus pesticides and pesticide containers.
Sheehan, Katharine A. 1996 Effects of insecticide treatments on subsequent 

defoliation by western spruce budworm in Oregon and Washington: 1982-92. Gen.

Tech. Rep. PNW-GTR-367. Portland, OR: U.S. Department of Agriculture, Forest

Service, Pacific Northwest Research Station. 55 p.

Effects of insecticide treatments conducted in Oregon and Washington from 1982

through 1992 on subsequent defoliation by western spruce budworm (Choristoneura

occidentalis Freeman) were evaluated by using aerial sketchmaps and a geographic

information system. For each treatment, the extent and severity of defoliation was 

calculated for the treated area and a set of four nested rings surrounding the treated

area (0-0.5 mile, 0.5-1 mile, 1-2 miles, and 24 miles) for up to 8 years: 3 years prior

to treatment, the year of treatment, and 4 years following treatment. lnsecticide treatments applied in 1982 and 1983 coincided with reduced percentages of defoliation by

western spruce budworm during the year following treatment. However, the percentage of defoliation usually returned to pretreatment levels by the second year, and 

defoliation severity in treated and adjacent untreated areas was nearly identical 

following treatment. For the period from 1985 through 1992, defoliation patterns 

(including both extent and severity) following treatment were generally similar in 

treated and adjacent untreated areas.

Keywords: Western spruce budworm, Choristoneura occidentalis, defoliation, 

insecticides, effects, suppression projects.

Abstract
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Western spruce budworm, Choristoneura occidentalis Freeman (Lepidoptera:

Tortricidae), is commonly regarded as one of the most important defoliators of western coniferous forests (Fellin and Dewey 1982, Furniss and Carolin 1977, Johnson 

and Denton 1975). Defoliation by budworm larvae feeding primarily on developing

buds and new foliage may lead to tree growth loss, topkill, and mortality (Van Sickle

1987).

Over 2.1 million acres have been treated with insecticides to suppress western spruce

budworm populations in Oregon and Washington since the current outbreaks began

in 1980 (appendix A). The objective of this analysis was to answer several questions

regarding the effectiveness of these treatments: What are the effects of treatment on

defoliation extent and severity in subsequent years? How long do the treatment effects last? Is there any evidence that budworms from untreated areas invade adjacent

treated areas after treatment? Answers to these questions would help managers 

evaluate the costs and benefits of using insecticides to suppress western spruce budworm populations.

Year-to-year changes in defoliation extent or severity do not necessarily reflect proportional changes in budworm density, because similar densities may result in a wide

range of defoliation levels (Campbell 1993). One year of defoliation observations 

alone also cannot be used to predict tree responses (for example, reduced growth,

topkill, mortality) because many other factors such as drought, previous defoliation 

history, and site conditions also affect tree responses (Crookston 1991, Nichols 1988).

However, economic analyses conducted during the environmental assessment process usually incorporate assumptions regarding defoliation patterns with and without

insecticide treatment (USDA 1987, 1991), and very little information is available to

quantify those assumptions.

Most insecticide treatments aimed at western spruce budworm from 1980 to the present were operational projects with no comparable untreated areas established to 

evaluate treatment effectiveness. A direct, statistically based evaluation of the effects

of treatment on subsequent defoliation therefore is not possible. Instead, defoliation

within treated areas is compared to defoliation in adjacent untreated areas.

In Oregon and Washington, aerial sketchmapping has been conducted annually since

1947 through a cooperative project involving both states and the USDA—Forest Service. In most years, all forested lands (both public and private) are surveyed during

July and August (Dolph 1980). Flying in reconnaissance planes at about 1,000 to

2,000 feet aboveground, two observers—each mapping a 2-mile swath on their side 

of the plane—sketch the location of insect and disease activity onto 1:126,720

(Oregon) or 1:100,000 (Washington) maps; the causal agent and severity are also

recorded for each polygon.1 In any given year, the aerial survey was always flown 

after any insecticide treatments scheduled for that year had been applied, and usually

after defoliation by the current budworm generation had been completed. Aerial

sketchmaps of defoliation by western spruce budworm were scanned or digitized for

1980 through 1994 as described by Sheehan (in press).

1 Personal communication. 1995. David R. Bridgwater, 

entomologist, Pacific Northwest Region, P.O. Box 3623, 

Portland, OR 97208-3623.

lntroduction

Analysis Methods

Observed Defoliation

1
Two systems for rating defoliation severity have been used during this period: either

three defoliation classes or four defoliation effects classes. Sketchmaps from 1980 to

1984 display three classes of defoliation severity: light, medium, and heavy. In 1985,

severity was not rated for most areas defoliated by western spruce budworm; the

unrated areas were arbitrarily assigned to the light defoliation class for this analysis.

From 1986 to the present, Oregon sketchmaps display four classes based on defoliation effects (1 = defoliation of current year foliage is visible from the air; 2 = defoliation is visible, some bare tops are present; 3 = many bare tops, though some foliage 

is present; 4 = most crowns are bare, virtually no foliage is left); most Washington

sketchmaps continue to display the three defoliation classes. The defoliation severity

ratings are intended to reflect the cumulative effects of several consecutive years of

defoliation. Defoliation should be mapped and rated for severity only in those areas

where budworm is currently active.

Most spray projects conducted from 1980 through 1993 were located in Oregon; 

therefore, results of this analysis are reported by defoliation class for 1980-84 and by

defoliation effects class for 1985-93. For graphs or analyses that reference observations from both periods, “light defoliation effects” refers to defoliation effects class 1

and light defoliation; “moderate defoliation effects” refers to defoliation effects class 2

and medium defoliation; and “severe defoliation effects” refers to defoliation effects

classes 3 and 4 plus heavy defoliation.

A total of 59 different projects aimed at western spruce budworm during 1980-93 

were identified (Hadfield 1992, 1994, [n.d.]; Howes and Wallesz [n.d.]; Ragenovich

1988; Sheehan [in press]; Skyler and others 1990). The three projects conducted 

in 1991 were primarily aimed at Douglas-fir tussock moth, Orgyia psuedotsugata

(McDunnough) (Lepidoptera: Lymantriidae), although western spruce budworm also

was present. Maps of the spray project areas suitable for digitizing could not be

obtained for 10 of those projects (covering about 32,570 acres, or 1.5 percent of the

total acres treated; see appendix B), and those projects were not considered further 

in this analysis. Spray project boundaries for the remaining projects were either

scanned or digitized from paper copies of the project as described in Sheehan (in

press).

For each spray project, the project boundary and four surrounding “rings” around the

project were delineated (fig. 1). The four rings were from 0 to 0.5 mile from the project

boundary, from 0.5 to 1.0 mile, from 1.0 to 2.0 miles, and from 2.0 to 4.0 miles from 

the project boundary. These rings were created by using a buffer command within a

geographic information system (GlS). Untreated areas inside the general project

boundary were assigned to the appropriate ring depending on the size of the untreated island. Projects treated in the same year and located within 4.0 miles of each

other were treated as one project for this analysis.

The location of each project relative to other projects conducted in different years was

also examined. Any portion of a project or ring within 1.0 mile of another project was

excluded from this analysis so that the effects of one spray project would not be confounded by effects of other projects. Two projects were dropped from the analysis

because over 95 percent of each project area was overlapped by projects conducted

in other years (Halfway: 4,217 acres treated in 1989 [100-percent overlap with the

1991 Hells Canyon-Pine-Catherine project], and Warm Springs: 71,172 acres treated

in 1993 [97-percent overlap with the 1988 Barlow-Dalles-Warm Springs-Hood River

County project]).

ldentifying Spray 

Projects and 

Surrounding Rings

2
Topological Analyses

3

Figure 1—The Canyon 1987 suppression project and four adjacent, surrounding “rings.” 

UP to 8 years of data were analyzed for each spray project: the 3 years preceding the

project, the year of the project, and the 4 years following the project. For each analysis year, a GIS (Arc/lnfo) was used to overlay’ the boundaries of the project area and

the four surrounding rings onto the observed defoliation by western spruce budworm

for that year. The number of acres defoliated was first summed by severity class for

the project area, the four surrounding rings, and the entire region. Four variables summarizing defoliation extent and severity were then calculated for each year:

Extent—

• Percentage of defoliation (percent defoliation) for the entire project or ring (all

severity classes combined)

Severity—

• Percentage of the defoliated area within a project or ring that was rated as light

defoliation or light defoliation effects
• Percentage of the defoliated area within a project or ring that was rated as 

medium defoliation or moderate defoliation effects

• Percentage of the defoliated area within a project or ring that was rated as 

heavy defoliation or severe defoliation effects

Differences among treated areas and adjacent rings were evaluated for both defoliation extent and severity. To quantify differences in defoliation severity, the absolute

value of the difference between a treated area and each surrounding ring was averaged for the 4 years following treatment for each project. When groups of projects

were evaluated (such as all projects conducted in 1982 and 1983), results from each

individual project were weighted by the area of that project (in acres).

About 2,195,000 acres were treated between 1982 and 1993 (fig. 2, appendix A),

including some areas treated more than once. The spray projects included in this

analysis represent a wide range of active ingredients, formulations, and application

rates (appendix B). The relative effects of different insecticides or formulations could

not be analyzed because so few treatments were replicated exactly.

A set of four graphs was prepared for each project (see appendix C). They display

defoliation extent or severity for up to 8 years (from 3 years prior to treatment to 4

years after treatment). One graph shows total percent defoliation (combining all 

severity classes) and the others show percent defoliation by severity class for the

treated area and the four surrounding rings. For reference, the first figure of appendix

C shows acres of defoliation by severity class for all of Oregon and Washington.

Visual inspection of the graphs shown in appendix C indicated that projects treated in

certain years resulted in similar defoliation patterns. Projects were then clustered into

four analysis groups based on year of treatment (fig. 3).

About 823,200 acres were treated in 1982 and 1983, 13.6 percent of which were

excluded from the analysis because they were within 1.0 mile of projects treated in

other years. Defoliation on the remaining ~711,200 acres was analyzed. Sevin-4-oil

was the most commonly used insecticide during these years (fig. 4).2

Projects conducted during 1982 and 1983 generally resulted in decreased percent

defoliation (all severity classes combined) within the treated area for 1 year after 

treatment (fig. 5). The average decrease in percent defoliation (change in percent of

the project area defoliated weighted by the acres treated during that project) for the

year following treatment was 64.1 percent (range = 0.4 to 100 percent). By the second year after treatment, percent defoliation had returned to levels within 10 percent 

of those reported during the year of treatment in all but one project and was higher

than in the year of treatment for 37.8 percent of the area analyzed for 1982 and 1983.

The one exception (Opal–1982) represented 2.2 percent of the area analyzed and 

was 100 percent defoliated during the third year after treatment.

2 The use of trade or firm names in this publication is for 

reader information and does not imply endorsement by the 

U.S. Department of Agriculture of any product or service.

Results

Projects: 1982-83

4
5

Figure 2—Acres defoliated by western spruce budworm (as recorded during aerial surveys) and acres 

treated with aerially applied insecticides, Oregon and Washington, 1980-94.

Figure 4—lnsecticides applied during projects conducted in 1982 and 1983: A = total treated area, and 

B = analyzed area (excludes treated areas within 1.0 mile of areas treated in other years).

Figure 3—Treated area (1982-93) partitioned into analysis groups: A = total treated areas, and B = 

analyzed area (excludes treated areas with no available maps or within 1.0 mile of areas treated in other

years).
6

Figure 5—Percent of treated area defoliated (all severity classes combined) for projects 

treated in 1982 and 1983, and average percent defoliation weighted by project area.

For most projects, percent defoliation (all severity classes combined) also decreased

for 1 year following treatment in the innermost surrounding ring but not the three outer

rings. Two projects (King-1983 and Pogue-P.A.-1983, representing 8.8 percent of the

area analyzed in 1982 and 1983) showed an increase in defoliation for the innermost

ring in the year after treatment. When weighted by project area, average percent defoliation within the inner ring decreased by 23.6 percent in the year following treatment. Percent defoliation in the outer three rings generally increased over time 

through 1986 as did the regional defoliation estimates, and those trends appeared to

be unaffected by the insecticide treatments.

Most projects were treated during the second year of extensive visible defoliation. 

Only one project (Pearson-1983, representing 3.6 percent of the area analyzed) experienced greater than 10 percent defoliation for more than 1 year prior to the year of

treatment. Defoliation during the year prior to treatment was generally rated as medium to heavy for 1982 projects and light for 1983 projects.

During the year of treatment and the following 2 years (for 1982) or 1 year (for 1983),

defoliation severity was generally light. For both treated areas and all surrounding

rings, less than 5 percent of the total area was rated as medium or heavy defoliation

with one exception (King-1983, representing 2.4 percent of the area analyzed). Defoliation was not rated in 1985 and thus was arbitrarily assigned to the light defoliation class for the graphs shown in appendix C. In 1986, defoliation severity was most

commonly rated as medium regardless of year of treatment.

During the 4 years following treatment, the average absolute difference between 

treated areas and surrounding rings for percentage of the area rated in a given severity class was calculated separately for each ring and severity class. Years when less

than 5 percent of the project area was defoliated were excluded from the analysis. For

all projects conducted in 1982 and 1983, the average difference (weighted by project

area) between treated areas and surrounding rings in percentage of the area rated in

a given severity class was less than or equal to 10 percent in all rings and severity

classes. In other words, defoliation severity within the treated areas following treat

ment was nearly identical to that observed within the surrounding rings, except when

very little defoliation occurred.
About 213,000 acres were treated in 1985 or 1987. About 7.9 percent of those acres

were excluded from the analysis because they were within 1.0 mile of projects treated

in other years, and 6.4 percent were not included because suitable maps for two projects (Boise Cascade-1986 and Burns-1987) were not available. Defoliation on the

remaining ~182,700 acres was analyzed. Thuricide 48LV was the most commonly

used insecticide during these years (fig. 6).

Figure 6—lnsecticides applied during projects conducted in 1985 through 1987: A = total acres treated, 

and B = analyzed acres (excludes treated areas with no available maps or within 1.0 mile of areas 

treated in other years).

For areas treated in 1985 or 1987, percent defoliation decreased sharply in 1987 and

generally remained low for at least 3 years. Average percent defoliation in treated

areas (all severity classes combined, weighted by the acres treated for each project) 

is shown in figure 7. Only one area (Flat-Dixie-1987, representing 35.5 percent of the

area analyzed in 1985 and 1987) was over 10 percent defoliated in 1987. This same

project was the only area to exceed 8 percent defoliation in any of the 4 years 

following treatment; it was rated as 48.4 percent defoliated in 1991.

Percent defoliation (all severity classes combined) also decreased sharply in the surrounding rings in 1987 for all areas treated in 1985 or 1987. For each project, year-toyear trends were similar for all four rings. Defoliation was less than 15 percent in all

rings for all projects in 1988 and 1989. In both 1990 and 1991, percent defoliation in

the surrounding rings remained low (less than 7 percent) in 54.2 percent of the area

analyzed, increased in 1990 to 29.4 percent and then declined to 0 percent in 1991 

for 10.3 percent of the area analyzed (Canyon-1987), and increased steadily to 51.2

percent in 1991 for the remaining 35.5 percent (Flat-Dixie-1987). In general, percent

defoliation was lower in the surrounding rings than in the treated area prior to treatment; during the year of treatment and in following years, percent defoliation in the

treated area and in the surrounding rings were very similar.

Defoliation severity was generally rated as light in 1984 and then moderate in 1986

(except for Starr-1987, representing 0.2 percent of the area analyzed, which increased to severe in 1986; severity was not rated in 1985). For those areas where

defoliation increased in either 1990 or 1991, or both years, severity was rated as light

or moderate. From 1984 through 1987, defoliation in treated areas was generally 

rated as either more severe than or identical to defoliation in surrounding rings; for 

the one exception (Burnt Cabin-Crooked-RaiI-Scotty-1985, representing 17.8 percent

of the area analyzed in 1985 and 1987), defoliation was less severe in the treated 

area in 1986, which was the year following treatment.

Projects: 1985-87

7
8

Figure 8—lnsecticides applied during projects conducted from 1988 through 1990: A = all treated areas, 

and B = analyzed areas (excludes treated areas with no available maps or within 1.8 mile of areas 

treated in other years).

Figure 7—Percentage of treated area defoliated (all severity classes combined) for 

projects treated in 1985 or 1987, and average percent defoliation weighted by project 

area.
From 1988 through 1991, percent defoliation was so low that differences in defoliation severity between treated areas and surrounding rings were difficult to evaluate.

When percent defoliation was greater that 5 percent, defoliation severity within the

treated area was very similar to that observed within the surrounding rings, with one

exception: Canyon-1987 (representing 11.1 percent of the area analyzed), in 1990,

when defoliation was rated as more severe in the outer two rings than in the inner 

two rings or treated area. Virtually no defoliation was reported in either the treated

areas or the surrounding rings from 1988 through 1991 for 54.2 percent of the area

analyzed, and in the remaining 45.8 percent of the area analyzed, percent defoliation

exceeded 10 percent in only one or two years.

In 1988 through 1990, about 761,000 acres were treated. About 5.6 percent of those

acres were excluded from the analysis because they were within 1.0 mile of projects

treated in other years, and no maps were available for 2.6 percent of the total area

treated. Defoliation on the remaining ~698,300 acres was analyzed. Thuricide 32LV

was the most commonly used insecticide during these years (fig. 8).

Percent defoliation (all severity classes combined) in areas treated from 1988 through

1990 generally decreased slightly in the year of treatment, then sharply in the year following treatment (fig. 9). In the one exception (Starkey-1988, representing 0.6 percent

of the area analyzed), percent defoliation decreased sharply in the year of treatment,

remained low during the year after treatment, and then returned to pretreatment levels

for the next two years. Percent defoliation remained low for 1 (0.6 percent of area 

analyzed), 2 (32.8 percent), or 3 (66.6 percent) years following treatment, then increased to either moderate or high levels (relative to percent defoliation prior to treatment). In some treated areas (Meacham-1988, Starkey-1988, and High Rock-1989,

together representing 7.3 percent of the area analyzed), defoliation declined sharply in

the fourth year after treatment. For these projects, defoliation averaged 13.6 percent

when weighted by project area, while in the remaining treated areas defoliation averaged 39.4 percent.

Figure 9—Percentage of treated area defoliated (all severity classes combined) for projects 

treated in 1988 through 1990, and average percent defoliation weighted by project area.

Projects: 1988-90

9
The defoliation trend in all four surrounding rings generally followed the same pattern

as for treated areas. For 19.3 percent of the treated area analyzed (Meacham-1988,

Starkey-1988, and Tollgate-1988), percent defoliation during the year after treatment

declined in the surrounding rings but remained higher than in the associated treated

areas. For those projects, the average decrease in percent defoliation from the year

prior to treatment to the year after treatment was 68.3 percent in the surrounding rings

compared to 97.2 percent for those projects (changes were averaged for all four rings

for each project and then weighted by project area). For the remaining 80.7 percent 

of the area analyzed, percent defoliation during the year after treatment averaged 

3.7 percent for treated areas and 7.4 percent for the associated rings (percent defoliation was averaged for all four rings and then weighted by project area).

Defoliation severity was generally rated as light or moderate before treatment, and 

ratings were either very similar or somewhat more severe in treated areas compared

to the four surrounding rings. In the 4 years following treatment, the average difference between treated and untreated areas in percent of the area rated in a given

severity class was less than 17 percent for all rings and severity classes (averages 

for all 1988-90 projects weighted by project area, excluding years when less than 

5 percent of the area was defoliated). Meacham-1988 (representing 5.1 percent of 

the area analyzed for 1988-90) had a consistently greater difference in severity ratings

for treated and untreated areas than the rest of the analyzed area, and relatively large

differences were found for High Rock-1989 (representing 1.1 percent of the area 

analyzed) in 1992 only. For most projects, though, there was little difference in defoliation severity between treated areas and surrounding rings.

About 400,000 acres were treated in 1991 through 1993. The primary target for the

1991 projects was Douglas-fir tussock moth, but western spruce budworm populations also were present in the treated areas. About 3.9 percent of the total area 

treated was excluded from the analysis because it was within 1.0 mile of projects 

treated in other years. Areas treated in 1993 (representing 16.7 percent of the area

treated from 1991 to 1993) were excluded because only 1 year has elapsed since

treatment; also, nearly all (96.5 percent) of the Warm Springs area treated in 1993 

was within 1.0 mile of a previous spray project. Defoliation on the remaining ~317,400

acres was analyzed. Thuricide 48LV was the insecticide most commonly used during

these years (fig. 10).

Percent defoliation (all severity classes combined) peaked in either 1991 (98.1 percent of treated area analyzed) or 1992 (1.9 percent) (fig. 11). Defoliation declined to

less than 2 percent in 1993 for all treated areas, and no defoliation was reported in

1994. Regional defoliation also peaked in 1991 and then declined steadily through

1994.

Percent defoliation in the four surrounding rings matched the pattern in the treated

area for all but one project. In the exception (Suttle—1992, representing 1.9 percent of

the area analyzed for 1991-93), defoliation in the surrounding rings peaked in 1992

rather than 1991 (when defoliation peaked within the treated area); no defoliation was

recorded in 1993 for either the Suttle project area or its associated rings.

Defoliation severity was rated as either predominantly light (28.4 percent of the area

analyzed) or a mixture of light and moderate (71.6 percent) both before and during 

the year of treatment. So little defoliation was recorded in the analyzed area during 

the years after treatment that differences in defoliation severity between treated areas

and surrounding rings could not be evaluated.

Projects: 1991-93

10
11

Figure 10—lnsecticides applied during projects conducted from 1991 through 1993: A = total 

treated area, and B = analyzed areas (excludes treated areas within 1.0 mile of areas treated in 

other years).

Figure 11—Percentage of treated area defoliated (all severity classes combined) for 

projects treated in 1991 and 1992, and average percent defoliation weighted by project

area.
In areas treated during 1982 and 1983, percent defoliation declined sharply for 1 year

following treatment within the treated area (and usually in the innermost ring) yet increased or remained nearly constant in the three outermost rings. The decreases in

percent defoliation commonly observed within the innermost surrounding ring during

this period might result from drift of insecticides from the treated areas into that ring.

For 98 percent of the area analyzed, percent defoliation returned to pretreatment 

levels (or higher) during the second year following treatment in the treated areas and

all surrounding rings. The remaining 2 percent of the area analyzed was 100 percent

defoliated during the third year after treatment.

Torgersen and others (1995) reported that in one of the treated areas (Aldrich-1983),

both budworm densities and defoliation declined in the year following treatment but

then rebounded to pretreatment levels by the second year after treatment. Despite 

one or two years of foliage protection, they found no differences in radial growth rates.

For 1982 and 1983 treatments, virtually no differences in defoliation severity were

found between treated areas and surrounding rings except when very little defoliation

occurred. Regional percent defoliation trends increased steadily during this period, 

and it is possible that the rapid return to pretreatment defoliation levels may have 

been caused by massive inflights of adult females from either the outer surrounding

rings or more distant sources.

For treatments conducted from 1985 through 1992, however, declines in percent defoliation within treated areas during or after the year of treatment were generally accompanied by very similar declines in all four surrounding rings. For 19 percent of the

area analyzed for 1988 through 1990 (10 percent of the area analyzed for 1985

through 1992), defoliation declined in adjacent rings but remained higher than in the

treated areas; however, even for those projects, defoliation in the adjacent rings declined by 68 percent, compared to a 97 percent decline in the treated areas. Similarly,

Powell (1994) reports no statistically significant differences in percent defoliation, 

topkill, or tree mortality between treated and untreated inventory plots in the Malheur

National Forest in Oregon. Powell examined some or all of the 1982, 1983, 1985, and

1987 projects included in this analysis (see Powell [1994] p. 73 and p. 83 for details)

Some observers have suggested that insecticide treatment may reduce the severity 

of subsequent defoliation in treated areas, thus providing benefits even when the 

number of acres defoliated is not reduced. For the entire period analyzed, however,

defoliation severity following treatment was generally very similar in both treated areas

and all four surrounding adjacent rings except when only a small percentage (less 

than 5 percent) of the area was defoliated. When percent defoliation is very low, a few

small polygons may greatly affect the defoliation severity graphs shown in appendix C

(graphs B through D).

Four explanations could account for similar defoliation patterns in both treated areas

and surrounding rings for projects conducted from 1985 through 1992: (1) aerial

sketchmaps may not detect real differences in defoliation extent or severity between

treated and untreated areas, (2) treatments may have caused effects in all four surrounding rings that were similar to effects caused within the treated area, (3) treatments may have removed major sources of budworm female moths that had been

sustaining defoliation in both treated areas and the surrounding rings, or (4) treatments may have had no net detectable effect on subsequent defoliation within treated

areas.

Discussion

12
The first explanation cannot be discounted because this analysis does not address 

the accuracy of aerial sketchmaps. Many spray project boundaries, though, have 

been based mainly on aerial sketchmaps—the boundaries are often placed where defoliation had been mapped previously. The overall quality of aerial sketchmaps differs

with observer experience, local weather conditions, regional fire activity, tree species

composition, and other local conditions. There is no reason to expect that aerial 

application of insecticides would affect subsequent sketchmap quality, however.

Sketchmaps judged adequate for identifying potential project boundaries therefore

should be adequate for evaluating the effect of those projects on subsequent defoliation. Further, Powell (1994) used on-the-ground surveys and found similar results for

projects conducted in the Malheur National Forest in 1982, 1983, 1985, and 1987: no

significant differences in either topkill or tree mortality between treated and untreated

plots.

The second explanation implies that extensive insecticide drift occurred, consistently

affecting areas up to 4 miles away from the target area. Where evidence of possible

insecticide drift was noted for 1982 and 1983 projects, that evidence was apparent

only within 0.5 mile of the treated area and not in the three outer rings. Given the 

small size of spray droplets and local conditions typical of budworm spray projects,

some degree of insecticide drift would be expected for most projects. It is highly

unlikely, though, that drift would consistently be so extensive that no attenuation of

effect was detected even 4.0 miles away from the project boundary.

The third explanation assumes that project boundaries were so accurately identified

that they encompassed those areas that (in the absence of treatment) export large

numbers of gravid females into the surrounding rings which otherwise would not experience as much subsequent defoliation. Following treatment, defoliation would decline in both treated and nearby areas because the major source of budworm eggs

(that is, females produced within the treated area) has been greatly reduced. Most

project boundaries are based on sketchmaps from previous years, vegetation information (mostly used to identify areas with significant portions of nonhost), ground-based

samples of budworm populations, and ecological and economic analyses of potential

effects. For many projects, large portions of the adjacent rings (especially the 

innermost ring) were defoliated in the year prior to treatment, and it is very unlikely 

that observers could accurately separate areas that export budworms (that is, potential treatment areas) from areas that import budworms (the surrounding rings under

this third explanation) during either ground or aerial surveys. In addition, although

adults are thought to disperse long distances (120 miles or more) in at least some

years (Campbell 1993), local weather is thought to have a greater influence on defoliation than adult dispersal in most years through its effect on host-budworm 

synchrony and subsequent larval survival (Shepherd 1985, 1994).

13
The fourth explanation—that treatments generally have no net detectable effect–is 

the most plausible and could result from several scenarios. In some cases, problems

with the application of insecticides (such as poor timing relative to budworm and foliage development, poor meteorological conditions during application) may have reduced insecticide efficacy such that any effect on subsequent defoliation was not detectable by aerial surveys. Many of the projects from this period (1985-92) were conducted in areas defoliated for several years; in these areas, budworm populations 

may have already begun to decline owing to other reasons (for example, increases in

natural enemy activity, decreases in foliage availability or quality), so that insecticide

treatments may have merely replaced other factors that would have reduced defoliation in subsequent years. In another scenario, budworm populations may have been

reduced in treated areas, only to have the effects of that reduction on subsequent defoliation masked by a massive outflight of adult females from both treated and untreated areas. Campbell (1993) reports that several years of extensive defoliation are

sometimes followed by apparent massive outflights of adult females—and many areas

treated during this period had sustained defoliation for 2 to 3 years. Different scenarios may have affected budworm defoliation patterns in different years or different projects, and in some cases, more than one scenario have operated concurrently.

Carbaryl was the most commonly used active ingredient for those treatments where

reduced percent defoliation was observed for 1 year; Bacillus thuringiensis (Bt) was

the most commonly used active ingredient for those treatments where little or no net

effect on defoliation was generally detected. Direct comparison of the two ingredients

is confounded, though, because different years (and therefore different weather regimes, different stages within the regional outbreak pattern, and so forth) also were

involved. This analysis therefore should not be used ta compare the relative 

effectiveness of the two insecticides.

The results of this analysis support the synthesis of Shepherd (1994), who writes 

that outbreaks of sustained defoliators such as western spruce budworm “...are 

often large in size, and high larval mortality is difficult to obtain consistently through

aerial spraying.” In general, the suppression projects conducted in Oregon and

Washington from 1982 through 1992 apparently reduced subsequent defoliation extent for 1 year at most. More commonly, there were little or no detectable differences

between treated and adjacent untreated areas in either extent or severity of 

defoliation .

Many thanks go to Shelly Hayden for digitizing historical records of both aerial survey

observations and suppression project boundaries. Julie Johnson rescued me from

many ARC dilemmas. Brian M. Spears initiated me into the mysterious world of 

ARC amls. James S. Hadfield, John W. Hazard, Timothy J. McConneil, David L.

Overhulser, and Torolf R. Torgersen critiqued an earlier draft of this manuscript, 

though I am responsible for any errors that remain. This analysis would not have been

possible without the annual aerial sketchmaps that are produced by a dedicated team

of aerial survey observers and mapping specialists. The aerial survey is an ongoing

cooperative project sponsored jointly by the States of Oregon and Washington and 

the USDA-Forest Service.

1 acre = 0.40 hectare

1 foot = 0.31 meter

1 mile = 1.61 kilometers

Conclusion

Acknowledgments

Metric Equivalents

14
Bridgwater, David. [n.d.]. Biological assessment of 1983 western spruce budworm 

suppression project. Portland, OR: U.S. Department of Agriculture, Forest Service

Pacific Northwest Region. 7 p. Unpublished report. On file with: Forest lnsects and

Diseases, Natural Resources, Pacific Northwest Region, P.O. Box 3623, Portland,

OR 97208-3623.

Campbell, Robert W. 1993. Population dynamics of the major North American 

needle-eating budworms. Res. Pap. PNW-RP-463. Portland, OR: U.S. Department 

of Agriculture, Forest Service, Pacific Northwest Research Station. 222 p.

Crookston, Nicholas L. 1991. Foliage dynamics and tree damage components of

the western spruce budworm modeling system. Gen. Tech. Rep. INT-282. Ogden

UT: U.S. Department of Agriculture, Forest Service, lntermountain Research

Station. 40 p.

Dolph, R.E., Jr. 1980. Budworm activity: Oregon and Washington: 1947-1979. 

R6-FIDM-033-1980. Portland, OR: U.S. Department of Agriculture, Forest Service

Pacific Northwest Region. 54 p.

Fellin, David G.; Dewey, Jerald E. 1982. Western spruce budworm. For. lnsect Dis. 

Leafl. 53. Washington, DC: U.S. Department of Agriculture, Forest Service. 10 p

Furniss, R.L.; Carolin, V.M. 1977. Western forest insects. Misc. Publ. 1339. Washington, DC: U.S. Department of Agriculture, Forest Service. 654 p.

Hadfield, James S. 1992. 1990 western spruce budworm suppression project: 

Yakima lndian Reservation. R6-90-03. Portland, OR: U.S. Department of

Agriculture, Forest Service, Pacific Northwest Region. 12 p.

Hadfield, James S. [1994]. 1993 Warm Springs lndian Reservation western spruce 

budworm suppression project-La Grande and Walla Walla Ranger Districts.

Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest

Region. 22 p. Unnumbered report. On file with: Forest lnsects and Diseases,

Natural Resources, Pacific Northwest Region, P.O. Box 3623, Portland, OR 

97208-3623.

Hadfield, James S. [n.d.]. 1992 Umatilla and Wallowa-Whitman National Forests 

western spruce budworm suppression project. Portland, OR: U.S. Department of

Agriculture, Forest Service, Pacific Northwest Region. 20 p. Unnumbered report.

On file with: Forest lnsects and Diseases, Natural Resources, Pacific Northwest

Region, P.O. Box 3623, Portland, OR 97208-3623.

Hostetler, Bruce B. [n.d.]. Biological assessment of 1982 western spruce budworm 

suppression project: progress report #1. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Region. 15 p. Unpublished report. On file

with: Forest lnsects and Diseases, Natural Resources, Pacific Northwest Region,

P.O. Box 3623, Portland, OR 97208-3623.

References

15
Howes, Steven W.; Wallesz, David. [n.d.]. 1992 Umatilla and Wallowa-Whitman 

National Forests western spruce budworm suppression project-Wallowa Valley

Ranger District. Portland, OR: U.S. Department of Agriculture, Forest Service,

Pacific Northwest Region. 17 p. Unnumbered report. On file with: Forest lnsects

and Diseases, Natural Resources, Pacific Northwest Region, P.O. Box 3623,

Portland, OR 97208-3623.

Johnson, Philip C.; Denton, Robert E. 1975. Outbreaks of the western spruce

budworm in the American northern Rocky Mountain area from 1922 through 1971.

Gen. Tech. Rep. INT-20. Ogden, UT: U.S. Department of Agriculture, Forest

Service, lntermountain Forest and Range Experiment Station. 144 p.

Nichols, Thomas J. 1988. The relationship between western spruce budworm 

defoliation levels and growth of individual Douglas-fir and grand fir trees. Forest

Science. 34(2): 496-504.

Powell, David C. 1994. Effects of the 1980s western spruce budworm outbreak 

on the Malheur National Forest in northeastern Oregon. Tech. Publ. 

R6-FI&D-TP-12-94. Portland, OR: U.S. Department of Agriculture, Forest 

Service, Pacific Northwest Region. 176 p.

Ragenovich, Iral. 1988. Operational and experimental use of Bacillus thuringiensis

for control of western spruce budworm in Oregon and Washington 1983-1987. 

R6-88-06. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific

Northwest Region. 16 p.

Sheehan, Katharine A. [In press]. Defoliation by western spruce budworm in Oregon 

and Washington from 1980 through 1994. Tech. Publ. R6-NR-TP-04-86. Portland,

OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Region.

Shepherd, R.F. 1985. A theory on the effects of diverse host-climatic environments 

in British Columbia on the dynamics of western spruce budworm. In: Sanders, C.J.;

Stark, R.W.; Mullins, E.J.; Murphy, J., eds. Recent advances in spruce budworms

research: Proceedings of the CANUSA spruce budworms research symposium;

1984 September 16-20; Bangor, ME. Ottawa, ON: Canadian Forestry Service: 

60-70.

Shepherd, Roy F. 1994. Management strategies for forest insect defoliators in British 

Columbia. Forest Ecology and Management. 68: 303-324.

Skyler, Patricia J; Roberts, Joy; Weatherby, Julie; Barry, John W. 1990. Aerial 

insecticide projects for suppression of western defoliators: 1970-1989; an 

annotated bibliography. FPM-90-11. Davis, CA: U.S. Department of Agriculture,

Forest Service, Forest Pest Management. 113 p.

Torgersen, Torolf R.; Powell, David C.; Hosman, Kevin P.; Schmidt, Fred H. 

1995. No long-term impact of carbaryl treatment on western spruce budworm 

populations and host trees in the Malheur National Forest, Oregon. Forest 

Science. 41-(4):851-863.

16
U.S. Department of Agriculture, Forest Service. 1987. Western spruce budworm 

management in Oregon and Washington during 1987: environmental assessment.

Portland, OR: Pacific Northwest Region. 73 p.

U.S. Department of Agriculture, Forest Service. 1988. Western spruce budworm 

Meacham pilot project-operations report, Umatilla National Forest, August 1988.

Pendleton, OR: Pacific Northwest Region, Umatilla National Forest. 259 p. Unnumbered report. On file with: Forest lnsects and Diseases, Natural Resources,

Pacific Northwest Region, P.O. Box 3623, Portland, OR 97208-3623.

U.S. Department of Agriculture, Forest Service. 1991. Umatilla and WallowWhitman National Forests: western spruce budworm: environmental assessment.

Portland, OR: Pacific Northwest Region. 75 p.

Van Sickle, G.A. 1987. Host responses. In: Brookes, Martha H.; Campbell, Robert 

W.; Colbert, J.J. [and others], coords. Western spruce budworm. Tech. Bull 1694.

Washington, DC: U.S. Department of Agriculture, Forest Service, Canada/United

States Spruce Budworms Program-West. 198 p.

17
Appendix A

18

Table 1—Acres defoliated by western spruce budworm

(as recorded during aerial surveys) and acres treated

with aerially applied insecticides in Oregon and\

Washington, 1980-94
Appendix B

19

Table 2—Characteristics of suppression projects conducted against western spruce burworm in Oregon and Washington, 1982-93 
20

Table 2—Characteristics of suppression projects conducted against western spruce burworm in Oregon and Washington, 1982-93 (continued)
21

Table 2—Characteristics of suppression projects conducted against western spruce burworm in Oregon and Washington, 1982-93 (continued)
22

Table 2—Characteristics of suppression projects conducted against western spruce burworm in Oregon and Washington, 1982-93 (continued)
Figure 12 summarizes defoliation by western spruce budworm in Oregon and Washington by severity class. For 1980 through 1984, severity was classified as light, 

medium, or heavy. In 1985, severity was not rated; all 1985 defoliation is shown in 

figure 12 as light for display only. For 1986 through 1994, defoliation was classified as

light, medium, or heavy in most of Washington, and as classes 1 through 4 for 

Oregon and the Blue Mountains in southwestern Washington. The four classes are

class 1 = defoliation visible from the air; class 2 = defoliation visible, and bare tops 

visible on some trees; class 3 = many trees with bare tops, though some green 

foliage present; and class 4 = most tree crowns bare, and virtually no foliage left.

The remaining pages summarize defoliation observed for one suppression project (or

several projects if located within 4.0 miles of each other and treated in the same 

year). Graph A (top left) shows the percentage of the total area that was defoliated 

(all defoliation classes combined) by year for the treated areas (solid diamonds), the 

0- to 0.5-mile ring (squares), the 0.5- to 1.0-mile ring (triangles), the 1.0-to 2.0-mile 

ring (“x”s), and the 2.0- to 4.0-mile ring (circles).

Graphs B through D show defoliation severity for the treated areas and the four surrounding rings. For that portion of the treated area or ring that was defoliated, graph 

B shows the percentage rated as light defoliation or light defoliation effects (class 1),

graph C shows the percentage rated as medium defoliation or moderate defoliation

effects (class 2), and graph D shows the percentage rated as heavy defoliation or

severe defoliation effects (classes 3 and 4).

Arrows mark the year of treatment. Specific projects are shown on separate pages in

chronological and alphabetical order.

Appendix C

23

Figure 12—Acres defoliated by western spruce budworm in Oregon and Washington by severity 

class.
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The Forest Service of the U.S. Department of 

Agriculture is dedicated to the principle of multiple 

use management of the Nation’s forest resources 

for sustained yields of wood, water, forage, wildlife, 

and recreation. Through forestry research, 

cooperation with the States and private forest 

owners, and management of the National Forests 

and National Grasslands, it strives—as directed by

Congress—to provide increasingly greater service 

to a growing Nation.

The United States Department of Agriculture (USDA) 

prohibits discrimination in its programs on the basis 

of race, color, national origin, sex, religion, age, disability,

political beliefs, and marital or familial status. (Not all 

prohibited bases apply to all programs.) Persons with 

disabilities who require alternative means of communication

of program information (Braille, large print, audiotape, etc.)

should contact the USDA Office of Communications at 

(202) 720-2791.

To file a complaint, write the Secretary of Agriculture, 

U.S. Department of Agriculture, Washington, DC 20250, 

or call (202) 720-7327 (voice), or (202) 720-1127 (TDD).

USDA is an equal employment opportunity employer.

Pacific Northwest Research Station 

333 S.W. First Avenue 

P.O. Box 3890 

Portland, Oregon 97208-3890

Sheehan, Katharine A. 1996. Effects of insecticide treatments on subsequent defoliation by western spruce budworm in Oregon and Washington: 1982-92. Gen.

Tech. Rep. PNW-GTR-367. Portland, OR: U.S. Department of Agriculture, Forest 

Service, Pacific Northwest Research Station. 55 p.

Effects of insecticide treatments conducted in Oregon and Washington from 1982 

through 1992 on subsequent defoliation by western spruce budworm (Choristoneura 

occidentalis Freeman) were evaluated by using aerial sketchmaps and a geographic 

information system. For each treatment, the extent and severity of defoliation was 

calculated for the treated area and a set of four nested rings surrounding the treated 

area (0-0.5 mile, 0.5-1 mile, 1-2 miles, and 2-4 miles) for up to 8 yean: 3 years prior

to treatment, the year of treatment, and 4 years following treatment. lnsecticide treatments applied in 1982 and 1983 coincided with reduced percentages of defoliation by 

western spruce budworm during the year following treatment. However, the percentage of defoliation usually returned to pretreatment levels by the second year, and 

defoliation severity in treated and adjacent untreated areas was nearly identical 

following treatment. For the period from 1985 through 1992, defoliation patterns 

(including both extent and severity) following treatment were generally similar in 

treated and adjacent untreated areas.

Keywords: Western spruce budworm, Choristoneura occidentalis, defoliation, 

insecticides, effects, suppression projects.