Classical biological control leads to long term declines in the rangeland invasive spotted knapweed

On-Demand

Presenting Author(s)

Chandra E. Moffat

Agriculture and Agri-Food Canada
Summerland, British Columbia, Canada

Co-Author(s)

DE

David J. Ensing

Agriculture and Agri-Food Canada
Summerland, British Columbia, Canada
RB

Robert S. Bourchier, PhD

Agriculture and Agri-Food Canada
Lethbridge, Alberta, Canada
Rosemarie A. De Clerck-Floate (she/her/hers)

Agriculture and Agri-Food Canada
Lethbridge, Alberta, Canada
Tyler Nelson

Agriculture and Agri-Food Canada
Summerland, British Columbia, Canada
VM

Val Miller

British Columbia Ministry of Forests, Lands, Natural Resource Operations and Rural Development, Range Branch, Operations Division
Nelson, British Columbia, Canada
ST

Susan Turner

British Columbia Ministry of Forests, Lands, Natural Resource Operations and Rural Development, Range Branch, Operations Division
Kamloops, British Columbia, Canada

Spotted knapweed (Centaurea stoebe ssp. micranthos) is a widespread and problematic invader of rangelands in southern British Columbia and much of the Pacific Northwest. Together with diffuse knapweed (C. diffusa), spotted knapweed has been the subject of a North American biocontrol programme since the 1970s, resulting in the release of 13 insect agents. Despite effective biocontrol of diffuse knapweed and widespread reductions in the density and fecundity of spotted knapweed, pockets of abundant spotted knapweed remain with considerable costs to rangeland tenure holders. Here we present ~30 years of knapweed density data from across the Canadian province of British Columbia which show considerable declines in abundance through time. In many sites, seed production falls below critical thresholds required for longer term population decline. Biological control agents are largely responsible for this decline, with >95% of almost 600 dissected plants exhibiting feeding damage to roots and / or seedheads. Our methodology provides a framework which can be used to guide long-term post release monitoring of weed biocontrol agents across study systems.