Forest Insect 

& Disease 

Leaflet 118

Revised May 2006

U.S. Department of Agriculture • Forest Service 

Balsam Woolly Adelgid 

Iral R. Ragenovich and Russel G. Mitchell 

The balsam woolly adelgid, Adelges piceae (Ratzeburg), is a tiny sucking insect 

that was introduced into North America 

from Europe. It probably first entered 

the Northeastern United States and 

Southeastern Canada around 1900. Later, it appeared on the West Coast (1929), 

and in the Southeastern United States in 

the mid 1950’s. Infested nursery stock is 

the presumed source of introduction. 

In Europe, host trees are relatively 

insensitive to attack and the insect is not 

considered a significant forest pest. In 

North America, however, it has caused 

significant damage and mortality to true 

firs (Abies spp.) in both eastern and western forests. In some localities, firs are 

slowly being eliminated from the ecosystem; and adelgid populations continue to 

spread to previously uninfested areas. 

Hosts and Distribution 

True firs are the only known hosts of the 

balsam woolly adelgid. Susceptibility 

ranges from highly sensitive to resistant, 

with North American species being the 

most sensitive to attack. European firs, 

especially European silver fir (Abies alba 

Miller), support large adelgid populations and yet remain relatively unharmed. Asian firs seem intermediate in 

sensitivity; some are damaged and some 

are not. 

Figs. 1a and 1b. Gouting caused by the 

balsam woolly adelgid. 
Fig. 2: Crown symptom shows crown decline and 

“fiddle-shape”. 

2 

In North America, infestations occur on 

balsam fir (Abies balsamea (L.) Mill.) 

in the northeastern United States and 

the Maritime Provinces of Canada; and 

bracted balsam fir (A. balsamea var. 

phanerolepis Fernold) and Fraser fir (A. 

fraseri (Pursh) Poir.) in the mountainous 

regions of Virginia, North Carolina and 

Tennessee. In the West, it occurs primarily on subalpine fir (Abies lasiocarpa 

(Hook.) Lindl), Pacific silver fir (A. 

amabilis (Dougl.) Forbes) and grand fir 

(A. grandis (Dougl.) Lindl.) in Oregon, 

Washington, Idaho and British Columbia. 

Subalpine fir and Pacific silver fir are 

infested in the mountainous areas and 

grand fir in the lowland valleys. See 

the map for the distribution of balsam 

woolly adelgid in North America (pg. 6 

& 7). 

Several other North American fir species, such as white fir (A .concolor (Gord 

and Glend.)Lindl.), noble fir (A. procera 

Rehd.) and Shasta fir (A. magnifica A. 

Murr) have shown signs of resistance in 

natural stands, but have been reported as 

being attacked by the 

adelgid in exotic or offsite plantings. 

Symptoms 

“Gouting” is a symptom 

of balsam woolly adelgid attack that occurs 

on North American firs. 

It appears as stunting 

of the terminal growth 

with distinct swellings 

around the buds and 

branch nodes (Figures 

1a and 1b). The larger 

swellings occur in the 

fastest growing parts of 

the crown, and on trees 

that have been lightly 

infested for a long 

time. Trees with this 

kind of injury decline 

slowly, often persisting for years. Growth 

is retarded and tree 

crowns often take on a 

“fiddle-shaped” appearance (Figure 2) or 

experience “top curl” 

(Figure 3). The dead, 

or dying, upper stem is 

often invaded by wooddestroying fungi. 

Another, more serious, type of attack is 
Fig. 3: Crown symptom showing “top 

curl”. 

the mass infestation along the main bole 

(Figure 4). Populations frequently reach 

densities of 100 to 200 adelgids per 

square inch of bark surface. Symptoms 

of decline vary somewhat with the tree 

species infested, but generally the foliage 

in a dying tree turns yellow, then deep 

red or brown. This sequence is particularly characteristic of infested balsam, 

Fraser, and subalpine fir. 

The habits of the insect and the response 

of the infested trees also appear to vary 

by region. In the West, stem-infested 

grand and Pacific silver firs generally 

have needle loss, followed by a change 

in color to a grayish-green and, ultimately, death. These trees often die quickly, 

sometimes after only 2 or 3 years of 

heavy infestation. Symptoms of gouting 

are seldom conspicuous in conjunction 

with stem infestations because of the 

trees’ weakened condition and the short 

period of infestation before tree death. 

In the Northeast, both gouting and stem 

attacks can be seen on the same tree, and 

trees with stem attacks can often survive 

for a decade or more. 

All sizes of trees are attacked, although 

trees that are pole-sized or larger seem 

most susceptible. In the West, stem 

infections are most abundant on the best 

sites, and crown attacks occur more 

often on poorer sites. In the Maritime 

Provinces of Canada, it appears that 

stem infestations are more abundant in 

the inland areas and crown attacks occur 

more often on the coastal areas. In New 

England, there does not appear to be a 

geographic pattern to the occurrence of 

the gout phase or the stem infestation. 

Bracted firs generally have gout infestations and Fraser fir has primarily sustained stem attacks. 

Fig. 4: Heavy stem infestion of balsam 

woolly adelgid along the stem of sub-alpine fir. 

3 
Effect on Host Trees 

Stem and twig injury is a result of the 

insect feeding on the host. The adelgid 

injects a substance into the bark that apparently affects the hormonal reaction of 

the tree and causes abnormal cell division 

and differentiation in the bark and newly 

formed wood. Giant parenchyma cells 

develop in the bark, and the cambium is 

stimulated to produce an abnormal number 

of phloem and ray cells. At the same time, 

an abnormally wide annual ring composed 

of cells with unusually thick walls is produced in the woody tissue. 

On twigs and branches, the abnormal cells 

cause a swelling, or gouting, at the nodes. 

These trees may live for many years, but 

growth is curtailed. Slowly, old needles 

drop and are not replaced by new ones. 

Cone and seed production is considerably 

reduced. 

Fig. 5: Compression-like wood in irregular 

outer rings caused by the trees reaction to 

feeding by the balsam woolly adelgid. 

Reddish, irregular growth rings, similar to 

compression wood, referred to as “rotholz” 

in the literature, occur in the stems of the 

trees that have heavy bole attacks (Figure 

5). This disrupts water conduction to the 

crown and often results in tree death within 

2-3 years after the attack. 

Fig. 6: Ventral view of balsam woolly 

adelgid. 

Life History and Behavior 

Balsam woolly adelgid populations in 

North America are composed entirely 

of females; as a result, reproduction is 

parthenogenetic (i.e. without mating and 

fertilization). Adults are tiny (about 1mm. 

long) dark purple to black, nearly spherical and wingless (Figure 6). They produce 

a thick mass of a waxy wool-like material that covers the body and protects the 

adult and her eggs (Figure 7). Some 100 

- 250 amber colored eggs are laid under 

this wool-like coat. An amber colored 

crawler hatches from the egg. The newly 

hatched crawler is the only stage capable 

of directed movement or dispersal. Long 

range spread is accomplished mainly by 

wind, although contact with birds and other 

animals may also contribute to natural dispersion. The crawler disperses and seeks 

a feeding site – most often bark lenticels 

and other roughened areas of the main 

stem, around branch and twig nodes, and 

the base of buds in the crown. It inserts its 

mouthparts into the bark and transforms, 

without molting into a flattened waxfringed resting stage known as neosistens. 

In the mountains, the neosistens is the only 

stage that will survive winter temperatures. 

Two immature forms closely resembling 

4 
the adult follow the neosistens. These 

two forms, plus the adult are called the 

sistentes. 

A rare stage, known as the progrediens has 

been observed in Europe and the Maritime Provinces of Canada. In one form, 

it is wingless and in another, winged. 

The wingless form is very similar to the 

sistentes. The winged form has membranous wings, five-segmented antennae, and 

generally lack wax pores. 

and early October, and egg laying continues 

until about mid- November. 

In some areas where temperatures are 

warmer and there are extended warm seasons, additional generations can occur. A 

partial third generation usually develops in 

North Carolina, and three generations with 

a partial fourth occur in the lowland areas 

of Oregon and Washington. 

Likewise, the extended months of colder 

Fig. 7: Balsam woolly adelgid eggs and crawler. Wool pushed aside for 

photographic purposes. 

The balsam woolly adelgid has 2 to 4 generations per year, depending on locality and 

elevation. Two generations are most common in mountainous areas of the West and 

throughout New England and the Maritime 

Provinces of the East. Spring development 

begins in late April or early May; by the 

end of June, most are in the adult stage. 

This is followed by an egg-laying period 

of about 6 weeks. In warm weather, eggs 

hatch within a few days, and the crawlers 

settle on the bark and transform into the 

resting, neosistens stage, which lasts from 2 

to 8 weeks. Adults of the second generation become abundant in late September 

winter temperatures and the shortened 

season of warmer temperatures that characterize some of the higher elevations, 

especially in the northern latitudes, can 

either result in fewer generations per year, 

or possibly limit the distribution of the 

adelgid entirely. 

Effects and Impacts 

In initial, intense infestations, when the 

adelgid first colonizes a stand, it encounters a reservoir of susceptible trees that has 

accumulated over many years. Since all 

adelgids are females, all individuals have 

the ability to reproduce, and population 

5
increases are exponential. These factors 

result in considerable spectacular tree mortality for several years (Figures 8a, 8b, and 

8c), and are characterized by stem attacks. 

After the initial wave of tree mortality, 

the effects of the adelgid become rather 

unspectacular because host is limited, 

populations fluctuate, it takes time for new 

trees to grow into a susceptible state, and 

environmental factors exert an influence 

on lower populations. It appears that once 

the adelgid colonizes a stand, it is there 

Range of balsam woolly adelgid infestation in North A

8a 8c

6 

Extensive tree mortality 

from balsam woolly 

adelgid following initial 

infestation. 

Fig. 8a: Individual tree 

mortality and fading 

trees. 

Fig. 8b: Extensive tree 

mortality. 

Fig. 8c: Older mortality 

with scattered dying 

trees. 8b 
America. 

permanently, and mortality continues on 

individual trees many years after the initial 

infestation. 

In areas where site, host, and environmental factors are not conducive to large 

population increases, chronic low-level 

infestations occur. These are more often 

characterized by gouting. New growth is 

halted in the crown, and cone and seed production is curtailed. These infestations can 

kill trees over time and decline is usually 

evidenced through varying degrees of top 

kill, poor crowns, and reduced reproduction (Figure 9). Trees that are weakened 

and have a poor live-crown ratio are more 

susceptible to the effects and impacts of 

other insects and disease agents. For example, moderate defoliation from western 

spruce budworm may result in significantly more mortality in stands infested 

by balsam woolly adelgid, than would be 

expected to occur in an uninfested stand. 

Although it is unlikely that the balsam 

woolly adelgid will eliminate its hosts entirely, it does present some local ecological 

problems. In harsh or disturbed environments, such as old lava flows, avalanche 

tracks and marshy meadows, subalpine fir 

acts as a pioneer species. By killing trees 

and inhibiting cone production, the balsam 

woolly adelgid has removed the subalpine 

fir from some of these local areas. In the 

lower Willamette Valley in Oregon, and the 

Puget Sound Trough in Washington State, 

long-time infestations in the bark cracks 

and along branches of large old grand firs, 

have gradually destroyed crown characteristics, cone crops are rare, and new 

reproduction is non-existent. As a result, 

grand fir is slowly disappearing from these 

ecosystems. In the East, balsam fir reproduction within infested fir stands is very 

good. However, much of the regeneration 

is heavily infested with the gout phase, and 

the future of that regeneration is uncertain. 

Fig. 9: Gradual tree decline evidenced 

through varying degrees of poor crowns, 

top kill and eventual mortality. 

7
In areas where host is limited or confined, 

such as the Fraser fir on scattered mountain- tops in the Appalachians, significant 

initial mature tree mortality occurred; however, Fraser fir regeneration is extensive 

(Figures 10a and 10 b). Stand characteristics have been changed, by changing the 

patterns of age and distribution of the fir. 

The effect of balsam woolly adelgid on 

this regeneration as it matures, remains to 

be seen, and it is possible that successive 

cycles of regeneration-mortality will result 

in decreasing numbers of trees over time. 

Photo by William Ciesla 

Photo by William Ciesla 

Figs. 10a and 10b: Fraser fir second-growth following extensive mature tree mortality 

from balsam woolly adelgid on Mt. Mitchell in North Carolina. 

8 
Management and Control 

Natural Predators and Parasites 

No parasites of the balsam woolly adelgid 

are known, but many predaceous enemies 

have been observed. Most North American 

predacious insects or spiders are general 

feeders and unreliable as control factors. 

They do not seem to concentrate on adelgid populations or fluctuate with adelgid 

population levels. 

Several species of insect predators have 

been introduced into North America from 

other parts of the world, primarily Europe. 

These include 3 beetles - Laricobius erichsonii (Rosenhauer) (Derondontidae); Pullus impexus (Mulsant) (Coccinellidae), and 

Aphidecta obliterata (L.) (Coccinellidae); 

and 3 flies - Aphidoletes thompsoni Mohn 

(Cecidomyiidae), Cremifania nigrocellulata (Czerny) (Chamaemyiidae), and Leucopis obscura Haliday (Chamaemyiidae). As 

yet, none of these predators have affected 

any detectable level of adelgid population 

control. They appear to feed on stages of 

the adelgid that are unimportant in determining trends in the adelgid populations. 

In initial stages of infestation, expanding 

adelgid populations increase so rapidly, 

and some tree species are so sensitive to 

attack, that predators have little chance of 

affecting any control before irreversible 

damage has been done. 

Environmental and Cultural Management 

The populations and effects of the adelgid 

may be limited on individual trees by the 

response of the tree itself. Stem-attacked 

trees that survive more than 1 or 2 years 

may form patches of a wound layer in 

bark that is still living, but impermeable 

to insect attack. Over time the adelgid 

populations are increasingly restricted to 

a smaller and smaller area until most adelgids die. Eventually, though, because the 

tree continues to grow and the protective 

layer becomes cracked, the tree is subject 

to re-infestation. 

Weather is also an important factor in affecting insect survival, particularly in the 

northern latitudes and higher elevations. 

In cold winters, only adelgids below the 

snowline will survive temperatures of below 30 degrees F. Subalpine firs growing 

close to timberline may not be as affected 

as trees at a lower elevation, because during short spring and summer seasons there 

is rarely enough heat accumulation for the 

insects to complete a second generation 

and allow good winter survival (only the 

resting 1st instar can survive the winter in 

the mountains). 

Stand and host susceptibility also appear 

to be related to other environmental factors such as elevation, stand age, and site 

condition. Some hosts such as grand fir are 

susceptible at low elevations, but rarely 

attacked at higher elevations. Pacific silver 

fir and subalpine fir also experience severe 

infestations at low elevations. At higher 

elevations subalpine fir experiences heavy 

infestations, but adjacent Pacific silver fir 

is rarely attacked. Mature Fraser fir is very 

susceptible, while younger trees do not appear to be as affected in natural conditions, 

but can be heavily infested in plantations. 

Species such as noble and red firs, that 

are resistant under natural conditions, can 

be attacked when planted in off-site and 

ornamental situations. 

The combination of host, site, and other 

environmental factors makes this a difficult insect to manage. For some tree 

species, reducing stocking and improving 

site conditions may reduce susceptibility; however, with other species, good site 

conditions make a species more susceptible 

to this insect. Hazard/Risk rating systems 

using site variables such as elevation, soil 

and site conditions, and stand conditions, 

developed for each individual tree species, 

can help identify those instances where a 

particular species would be most susceptible, and those situations where other 

species may survive. Where possible, the 

land manger should select against susceptible or infested individuals and favor more 

tolerant, or non-host species, either through 

selection harvest or planting. 

9
In Christmas tree plantations or other highvalue situations removing infested trees 

(if there are only a few individuals) and/or 

direct control can reduce the impact of the 

balsam woolly adelgid. 

Direct Control 

The adelgids are hidden in protective niches of the bark and branches of trees and 

are individually protected by their woollike waxy exudation. Applying contact 

insecticides effectively by aerial spraying 

over large areas is not possible. However, 

spraying individual trees from the ground 

with an approved insecticide has proved 

effective for control. 

Contact insecticides are most effective 

against the exposed crawler stage and are 

applied as a bark drench with a hydraulic 

sprayer in May through June and September through October. Some of the insecticidal soaps and oils can penetrate the waxy 

coating of the adult adelgids, however, 

timing of application is important, in order 

to avoid burning the foliage on the tree. 

Treatment will reduce populations to below the tree-killing level, and some treated 

trees may remain generally free from 

adelgids for several years. 

Spraying is warranted only in accessible 

areas supporting relatively high-value 

trees. Some systemic insecticides are registered for adelgid control and may be effective on balsam woolly adelgid. Contact 

local extension agents or forest entomology experts for the currently registered and 

most effective insecticides. 

References 

Amman, Gene D. 1962. Seasonal biology 

of the balsam woolly aphid on Mt. Mitchell, North Carolina. J. Econ. Entomol. 

55(1):96-98. 

Amman, G.D. and Charles F. Speers. 1965. 

Balsam woolly aphid in the southern Appalachians. J. Forest. 63:18-20. 

Amman, Gene D. and Robert L. Talerico. 

1967. Symptoms of infestation by the 

balsam woolly aphid displayed by Fraser 

fir and bracted balsam fir. USDA Forest 

Serv. Southeast. Forest Exp. Sta. Res. Note 

SE-85. 7p. 

Balch, R.E. 1952. Studies of the balsam 

woolly aphid, Adelges picea (Ratz) and its 

effects on balsam fir, Abies balsamea (L.) 

Mill. Can. Dept. Agric. Pub. 867. 76p. 

Carroll, W. J. and D. G. Bryant. 1960. A 

review of the balsam woolly aphid in Newfoundland. Forest. Chron. 36:278-290. 

Foulger, A. N. 1968. Effect of aphid infestation on properties of grand fir. Forest 

Prod. J. 18(1):43-47. 

Johnson, Norman E., Russell [Russel] G. 

Mitchell, and Kenneth H. Wright. 1963. 

Mortality and damage to Pacific silver fir 

by the balsam woolly aphid in southwestern Washington. J. Forest. 61: 854 - 860. 

Livingston, R. L.; J. E. Dewey; D. P. Beckman, and L. E. Stipe. 2000. Distribution of 

the balsam woolly adelgid in Idaho. West. 

J. of Applied Forest. 15(4):227-231. 

Mitchell, Russel G. 1966. Infestation characteristics of the balsam woolly aphid in 

the Pacific Northwest. USDA Forest Serv. 

Pacific Northwest Forest and Range Exp. 

Sta. Res. Pap. PNW-35. 18p. 

Mitchell, Russel G. and Paul E. Buffam. 

2001. Patterns of long-term balsam woolly 

adelgid infestations and effects in Oregon 

and Washington. West. J. of Applied Forest. 16(3): 121-126. 

Mitchell, Russel G., Norman E. Johnson, 

and Julius A. Rudinsky. 1961. Seasonal 

history of the balsam woolly aphid in the 

Pacific Northwest. Can. Entomol. 93: 

794-798. 

Mitchell, R. G. and K. H. Wright. 1967. 

Foreign predator introductions for control 

10
of the balsam woolly aphid in the Pacific 

Northwest. J. Econ. Entomol. 60(1): 140-

147. 

Smith, George F. and N. S. Nicholas. 

2000. Size- and age-class distributions of 

Fraser fir following balsam woolly adelgid 

infestation. Can. J. For/. Res. 30: 948-

957. 

Turnquist, R. and J. W. E. Harris. 1993. 

Balsam woolly adelgid. Can. Forest. Serv. 

Forest Pest Leaflet. 4p. 

Witter, John A. and Iral R. Ragenovich. 

1986. Regeneration of Fraser fir at Mt. 

Mitchell, North Carolina, after depredations by the balsam woolly adelgid. Forest 

Sci. 32 (3): 585 – 594. 

Acknowledgements 

Map: Information provided by: Nelson 

Carter - Canadian Forest Service, James 

Linnane - USDA Forest Service Northeastern Area, and Dave Trotter - British Columbia Ministry of Forests. Map produced 

by Sundi Sigrist - USDA Forest Service. 

Photos: Figures 1a, 2, 3, 4 and 5 - Oregon 

Department of Forestry. Figures 1b, 6, 

7, 8b and 9 - Washington Department 

of Natural Resources. Figures 3 and 8c 

- USDA Forest Service. Figure 8a - Idaho 

Department of Lands. Figures 10a and 10b 

- William Ciesla. 

Review: Kyle Lombard, New Hampshire 

Division of Forests and Lands, David 

Overhulser, Oregon Department of Forestry 

11 
Pesticides used improperly can be injurious to humans, 

animals, and plants. Follow directions and read all 

precautions on the labels. Consult your local forest 

pathologist, county agricultural agent, or State extension 

agent about restrictions and registered uses of particular 

pesticides. 

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