Forestry Branch
Spruce Budworm in Manitoba
In Manitoba the spruce budworm, Choristoneura fumiferana, is a serious defoliator of balsam fir, white spruce and occasionally black spruce. The larva or caterpillar stage mines old needles, feeds on buds and the current year's needles from early May to late June. Heavy feeding gives trees a scorched appearance by the end of the feeding period.
Repeated loss of new foliage over a few years weakens trees making them more susceptible to secondary insects and disease. Branch dieback and top kill frequently occur. Balsam fir often die following three or four years of severe defoliation. White spruce, which is more tolerant of budworm feeding, may die after five or six years of severe defoliation.
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In 2008, defoliation of spruce/fir forests by spruce budworm occurred mainly in Riding Mountain National Park and in the northwestern and northeastern parts of the province.
Egg mass surveys were carried out to predict defoliation for 2009. Generally light defoliation (up to 35 percent defoliation of the current year's foliage) is predicted for Whiteshell Provincial Park, Nopiming Provincial Park, the Tembec Inc. Forest Management License area, Duck Mountain and northwestern Manitoba. In the Interlake, moderate defoliation (35 percent to 70 percent defoliation of the current year's foliage) is predicted for Grindstone Peninsula and severe defoliation (greater than 70 percent of the current year’s foliage) is predicted for the Spruce Sands area. Severe defoliation is also predicted for Spruce Woods and Paint lake Provincial Parks.
Control measures are usually recommended where moderate or severe defoliation is expected. Chemical insecticides often used to combat the spruce budworm include dimethoate and malathion. These products kill budworm either on contact or by ingestion. Biological pesticides, such as Bacillus thuringiensis, and reduced risk pesticides, such as Mimic, may also be used. Budworm cease feeding and die when these products are ingested. Successful control can be achieved using ground spray equipment if the majority of the trees on the property are accessible from the ground and if the treetops can be reached with this type of equipment. In many cases aerial spraying may be the most viable option. The timing for control varies from year to year, but is generally late May to mid June, when new shoots have elongated and are flaring open. Information regarding the appropriate timing of insecticide application is available from the Forestry Branch. All insecticide products should be used in accordance with the manufacturer's label recommendations.
Insecticide application is not worthwhile on properties where trees have declined past the point of recovery or where spruce budworm host tree species are not present. Aerial application should not be attempted where the host tree species are in the understorey below broad-leaved trees. In this situation very little of the insecticide can reach the host tree foliage and the budworm.
For more information on the spruce budworm please call the Forestry Branch at 945-7868.
