Balsam Woolly Adelgid

The balsam woolly adelgid, Adelges piceae (Ratz.), was accidentally introduced to North America from Europe. The adelgid is an inconspicuous, aphid-like pest that appears as white, woolly masses about 1 mm long on the bark.

Due to their small size, they can be easily overlooked in the early stages of an infestation. They feed exclusively on true firs (Abies species). Despite its small size, it is an extremely destructive pest that can kill a tree after several years of heavy feeding. This is especially true for subalpine fir (Abies lasiocarpa).

Symptoms

The balsam woolly adelgid injects saliva into its host plant when feeding. The saliva is toxic to the plant and inhibits bud formation and causes long-term tree decline. Symptoms of adelgid feeding include needle yellowing and premature needle loss, and swelling of branch nodes and terminal buds.

balsam woolly adelgid damage to fir
Balsam woolly adelgid damage to fir. 

Life Cycle

The adelgid has two to four generations per year. The wingless female can produce in excess of 200 amber colored eggs. The eggs are laid under masses of "cottony tufts" on the underside of branches and on the trunk. Crawlers are visible with the aid of a hand lens beginning around bud break. This stage is the most susceptible to chemical control. There are no males, hence females give rise to more females.

Host and Geographical Range

Balsam woolly adelgid attacks only Abies or true fir species. North American species are the most sensitive to attack, led by Fraser fir, subalpine fir, balsam fir and Shasta fir. Grand and amabilis firs are less susceptible. European silver fir is relatively resistant.

The adelgid is an important pest of true firs in the Atlantic provinces, the NE and NW United States and SW British Columbia. There is tremendous concern it will spread into the Interior and infest the very important and widely distributed subalpine fir forests. There is a provincial regulation that restricts the movement of true firs within B.C. to reduce the risk of balsam woolly adelgid spreading into the Interior of B.C.

Regulations

The movement of true firs for use in reforestation, or as an ornamental or a Christmas tree, poses a significant risk of spreading this pest. To reduce this risk, all true firs must be grown under permit. Annual permits expire on December 31st and can be obtained from the Entomologist with the British Columbia Ministry of Agriculture in Abbotsford.

Trees grown outside the quarantine zone (Figure 1) have free movement within the province. True firs grown in the quarantine zone cannot be shipped outside the zone within British Columbia. There are no restrictions on the domestic movement of true firs outside of British Columbia. Sale and movement of cut trees or foliage of true firs grown in the quarantine zone is prohibited between January 31 and November 1 anywhere in the province. Cones and seeds are exempt from this regulation. When moved between November 1 and January 31, cut Christmas trees, boughs for wreaths or decorations, and cones are also exempt from zone restrictions.

Figure 1. Areas within British Columbia regulated for Balsam Woolly Adelgid.

quarantine map

Management

There are no effective naturally occurring biological control agents for BWA in B.C.. Control includes removal and disposal of infested trees. Insecticides may have only limited impact, however efficacy trials are underway in B.C..