Western spruce budworm management
On this page:
Populations are monitored annually, they only require management when outbreaks occur. Outbreaks can last more than 25 years.
Outbreaks have been recorded in British Columbia's interior forests from the early 1900s up to the present. For example, in 1987 the budworm attacked more than 800,000 ha of forest, mostly in the southern interior.
Outbreaks in susceptible interior forests are influenced by weather, and can fluctuate in an irregular and unpredictable fashion.
Long-term management consists of stand-manipulation tactics, including:
- Conversion to alternative species
- Promotion of species mixes
- Stand structure manipulation (harvesting, thinning, spacing, underburning)
- Stand improvement (fertilization)
Alternative species are less susceptible to budworm feeding. Even-age silviculture systems (clearcut, seed tree, shelterwood) can work in appropriate ecosystems in conjunction with the promotion or planting of alternative species. Species less susceptible to western spruce budworm include: western larch, lodgepole and ponderosa pine and spruce. All other species commonly grown in B.C. (excluding Douglas-fir and true firs) can be considered non-hosts.
Mixed species, in single or multi layered stands, are likely to sustain shorter and milder outbreaks. In ecosystems where uneven-age or multi-layered stand management is the desired silvicultural system, or is the only option, species mosaics should be promoted where possible.
Silviculture and treatment prescriptions that promote species mixes include:
- Patch cut and plant
- Partial cutting (selective cuts, thinning, spacing)
For example, partial cutting regimes could retain a lodgepole and/or ponderosa pine component within an existing stand, thus encouraging future establishment of these species.
Manipulation of stand structure is an important tactic. High stand-densities increase stand hazard by providing an abundance of new foliage for larvae. Stocking and density control facilitate rapid growth of individual trees and permit selection of genetically superior trees more tolerant of defoliating insects.
Density control can be achieved through harvesting and silviculture treatments such as thinning, spacing and under-burning. Greater inter-tree distances achieved through density control promote full crowns and more vigorous growth so that tolerance to budworm feeding is enhanced. Attempts should be made to minimize large, full-canopy trees overtopping smaller, less foliated trees. Overstorey trees provide a means of budworm dispersal down onto trees growing under the canopy radius.
Fertilization for stand improvement can promote full crowns and increased tree growth. The relationship of forest fertilization to budworm defoliation is not fully understood at this time.
Foliage protection and population reduction are short-term direct-control strategies that utilize chemical or biological insecticides. Direct control should be considered when moderate to severe defoliation is predicted in a stand for the following year.
Several biological and chemical insecticides are registered for use against the western spruce budworm. Timing of insecticide treatment should coincide with peak fourth or fifth instar, depending on treatment objectives. Biological insecticides have proved very successful. Environmental impact is minimal and efficacy is high, provided the insecticide is applied correctly and in time.
The southern interior's proactive integrated pest management program involves the detection, identification, monitoring, mitigation and control of various defoliating insects.