Controlling Weeds Using Biological Methods


Since 1952, over 50 insects and pathogens have been released in B.C. to control more than 20 introduced weed species. Introduced agents include aphids, beetles, moths and flies. The time required for agents to establish and effectively control the target noxious weed has varied depending on the agent, the site and the environmental conditions at the time the agent was released. Most noxious weeds require more than one agent for successful control. Agents have been released on the following noxious weeds:

Diffuse and Spotted Knapweed

Knapweeds are widely distributed in the province, infesting more than 80 000 hectares of rangeland and significantly reducing the amount of forage available for wildlife and grazing livestock. Both noxious weeds contain extremely bitter tasting oils. Twelve biological control agents have been introduced to control these plants. Of these, five are root feeding insects and seven attack the seed head.

Aphthona nigriscutis (shown in its larval and adult stages) is used to control leafy spurge.

Leafy Spurge

This perennial weed occurs in isolated pockets in the Thompson, Cariboo, Boundary, East Kootenay, Nechako, North Okanagan and Bulkley Valley areas. It contains a milky-coloured juice that can poison livestock. Five biological control agents are available to control leafy spurge. Two root feeding flea-beetles and a moth are established in the field. Leafy spurge is under control by one of the root feeding fleabeetles on restricted habitats throughout the province.

Spurge before
Leafy spurge (Euphorbia esula L.) before release of the biological eontrol agent (30/ 6/89).

Spurge after
Leafy spurge after the release of Aphthona nigriscutis (1/7/93).

Yellow and Dalmatian Toadflax

These perennial weeds spread by seed and creeping roots. Toadflax is distributed throughout the Okanagan, Similkameen, Thompson, East Kootenay and Cariboo areas. Two root feeding insects, two seed head feeding agents and one stem feeding insect are being raised at the Kamloops facility for control of toadflax. Plans are being made for initial field release.

Dalmation toadflax (Linaria dalmatica)

Mecinus janthinus (shown in its larval and adult stages) is used to control yellow and dalmation toadflax.

Hound's Tongue

Hound's tongue is toxic to livestock and some wildlife. Four agents are being screened for this biennial weed that infests open forest sites, roadsides and other disturbed areas. Plots have been established at the propagation facility to receive the agents once they are approved for release.

Hound's tongue (Cynoglossum officianle L.)

[Previous Section] [Table of Contents] [Next Section]

[Forest Practices Branch]