Silviculture - There are a variety of silvicultural management practices available to prevent or reduce the impacts of the western 

spruce budworm. These include both even– and uneven-aged regeneration systems, and intermediate treatments on stands not ready for harvest. The most serious damage, particularly on small or younger forests, occurs in relatively pure stands of Douglas-fir or stands with a mixture of true firs and Douglas-fir. Thus, the susceptibility of some forests may be minimized by increasing the complement of non-host species and reducing the percentage of Douglas-fir and true firs. Hardwood trees and pines are not hosts for this insect and even spruce is not a preferred host. Maintaining a healthy forest or tree provides the best natural defense for preventing or reducing the severity of western spruce budworm outbreaks. Providing diverse habitat for insectivorous birds, mammals, and other insects may minimize or prevent western spruce budworm outbreaks. Proper snag management, leaving adequate woody residues on the site, and enhancing the edge effect, diversifies habitat. Natural predators and parasites are not as effective during outbreaks as they are when populations are at lower levels. Their presence at low population levels may prevent an outbreak from occurring. 

 Pesticides used improperly can be injurious to 

 humans, animals, and plants. Follow directions 

and read all precautions on the label. Consult your 

local county agriculture agent or State extension agent 

about restrictions and registered used of particular pesticides. 

USDA is an equal oppo 

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Managing 

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M anagement Options anagement Options anagement Options Western spruce budworm populations usually are kept low by a combination 

of predators, parasites, adverse climatic conditions, or inadequate food supply. Spiders, insects, and a variety of birds are important predators. Adverse weather conditions, particularly sudden freezes in late spring, may kill large numbers of larvae. A major factor in ending long-term outbreaks appears to be starvation from inadequate or nutritionally poor food sources. However, this may not be a factor in urban situations. Cultural practices such as thinning, watering, and fertilizing, which promote tree vigor, may help trees survive repeated attacks. 

Microbial insecticides - A microbial insecticide registered for use against the western 

spruce budworm is the bacterium Bacillus 

thuringiensis (BT), a naturally occurring, hostspecific pathogen that affects only the larvae 

of lepidopterous insects. It is environmentally safe to use in sensitive areas such as campgrounds or along rivers or streams where it may not be desirable to use chemical insecticides. Users should contact State or Federal Forest Health Specialists regarding formulations, dosages, and timing of treatment. 

 Chemical insecticides - When necessary, 

western spruce budworm populations can be substantially reduced with chemical insecticides. Large forested areas can be aerially sprayed for short-term protection, and individual trees can be sprayed using ground equipment. Chemicals currently registered for use against the budworm include acephate, malathion, carbaryl, and methomyl. If spraying is needed, State or Federal Forest Health Specialists should be consulted for treatment timing, formulations, dosages, and the most current information on registered insecticides. 
Late instar stage 

of the western 

spruce budworm 

management alternatives to reduce western spruce budworm impacts is the focus of this brochure. 

Adult and 

pupal stages 

of the western spruce 

budworm. 

D escription escription The western spruce budworm passes 

through four distinct life stages: egg, larva, pupa, and adult. Eggs are oval, light green, 

and about 1.2 mm long and overlap like shingles. Larvae pass through 6 stages of development (instars) as they mature. They start out 

very small, yellow-green in color with a brown head, and finish as a 1 to 1-1/2” olivebrown caterpillar also with a brown head. Each body segment of the mature larva is marked with a pair of ivory-colored spots. Pupae are 1/2” to 5/8” long, brown, broad at the head end and narrow toward the tail. They are brownish-yellow or brownish-green at first, and later turn reddish-brown. Adult

moths are about 1/2” long and have a wingspread of about 1”. They are typically small, mottled, rusty-brown in color, but color may vary from tan to nearly black. 

I ntroduction ntroduction ntroduction Western spruce budworm is the most com- mon and widespread insect defoliating 

Douglas-fir and true firs in the west. Larvae will also feed on pines and other conifers when populations reach outbreak levels. Larvae initially feed on new needles throughout late spring and early summer causing a redhalo appearance on outer portions of infested branches.  Defoliation from budworm is most damaging in Douglas-fir and true fir forests that are uneven-aged or have multiple canopy layers. Large outbreaks have occurred across the West because of the current abundance of Douglas-fir and true firs in forests. Historically, the range of Douglas-fir and true firs, and associated budworm outbreaks, were limited by periodic fires. Length of outbreaks can range between 5 and 30 years depending upon site quality and available hosts.  Damage from defoliation can result in reduced vigor, growth loss and increased susceptibility to attack by other insects and diseases. Mortality from repeated and heavy defoliation rarely exceeds about five percent of large mature trees and is typically confined to smaller, suppressed and pole-sized trees. Outbreaks of budworm can be prolonged, and defoliation more severe during periods of drought. Bark beetle attacks on heavily defoliated trees may be higher during periods of drought.  Heavy budworm caused defoliation can result in increased fire risk over the shortterm and impact visual quality of forested areas near homes and along scenic corridors. Although large numbers of trees with red needles can increase the short-term risk of wildfire, small tree mortality resulting from heavy budworm defoliation can result in reduced fire hazard over the long-term.  There are several management options to reduce damage and potential mortality from western spruce budworm. These include thinning forests to reduce the number of canopy layers and spraying with insecticides. The life history, effects of defoliation, and 

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