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No. 51 March 6, 1993
Address: aceska at cue.bc.ca Victoria, B.C.
BIOLOGICAL WEED CONTROL IN BRITISH COLUMBIA (Part 1 of 2)
From: Roy Cranston, B.C. Ministry of Agriculture
<rcranston at galaxy.gov.bc>
British Columbia is heavily committed to the use of natural
agents to control noxious grassland and pasture weeds. From
modest beginnings in 1951 with the introduction of a beetle to
control the poisonous weed St. Johnswort, 50 agents have been
released against 17 weed species to over 2,000 sites in B.C.
Significant progress has been achieved in biocontrol development
through the cooperative efforts of the International Institute
of Biological Control (Switzerland), Agriculture Canada, the
Ministries of Agriculture, Fisheries and Food and Forests and
through support of private sector groups such as the B.C.
* Candidate natural agents that feed on a targeted weed and show
promise for control are studied in their native habitat.
* Exhaustive studies are carried out to ensure the insect will
attack only the targeted weed and not other vegetation.
* Long term results are reviewed by North American Biocontrol
agencies. If the natural agent is proven to damage the weed
without attacking other vegetation it is approved for release
in Canada and the United States.
* The B.C. Plant Protection Advisory Council approves or rejects
release of federally approved natural weed control agents to
* Initial B.C. releases are made under controlled conditions for
the purpose of gaining establishment and to increase
populations for provincial redistribution.
Usually several species are released to improve the chances of
long-term control of the weed. The B.C. Ministry of Forests,
Range Branch, maintains bioagent propagation facilities at
Kamloops and Castlegar. When populations warrant, the insects
are then redistributed throughout the province. The Ministry
of Agriculture, Fisheries and Food maintains computer and map
records of all weed bioagent releases and redistributions.
Reductions in density, seed production and spread potential are
realities for some weeds now and the possibility for success
against other species is encouraging. St. Johnswort, nodding
thistle and Bull thistle are under effective biocontrol in the
province and no longer require herbicide treatment. Knapweed
densities are beginning to decline dramatically at a number of
Use of natural agents will continue to play an integral and
expanding role in integrated vegetation management systems in
British Columbia and will result in less need for chemical,
cultural and mechanical control programs.