RMD-13-04: Consolidated Pest Risk Management Document for pest plants regulated by Canada
Appendix 4B: Risk Management Considerations for Centaurea solstitialis (yellowstar-thistle)

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Values at Risk

Rangelands: Rangelands are important ecosystems that provide an abundance and variety of products, such as browse and forage for both wild and domesticated animals and wood fibre. Rangelands also provide drinking water, habitat for wildlife, biodiversity, nutrient cycling and recreational opportunities (Horton 1996). Centaurea solstitialis has the ability to invade rangelands, reducing their native biodiversity, wildlife habitat and forage and affecting the natural water cycle. One of the most common and profitable uses of rangeland is livestock grazing. Table 11 shows the number of cattle and calves, sheep and lambs and horses and ponies in areas of B.C. in hardiness zones five to nine. Of concern is that Centaurea solstitialis is toxic to horses if consumed in large amounts and can interfere with livestock grazing and is recognized as one of the "worst weeds in the West" by the Centre for Invasive Plant Management (CIPM 2009).

Potential Mitigation Measures for Natural Means of Dispersal

Natural dispersal is a possible pathway of entry of Centaurea solstitialis into Canada, particularly into British Columbia. Currently, there are four bordering counties in Washington, one bordering county in Idaho and one bordering county in Montana (adjacent to B.C.) that are infested with the weed (USDA-NRCS 2009). It is listed as a Class B Noxious Weed in the State of Washington (NWCB 2009), a noxious weed in Idaho on the Statewide Containment List (ISDA 2009) and a Category 3 noxious weed in Montana (MDA 2009). In Washington and Idaho, the goal is to prevent the spread of existing populations and the establishment of new populations, but not necessarily eradication. In Montana, a management criterion of Category 3 noxious weeds includes awareness and education, early detection and immediate action to eradicate infestations. Depending on how close existing populations are to the border, these programs could reduce the risk of Centaurea solstitialis naturally dispersing into Canada. It is also regulated as a noxious weed under the B.C. Weed Control Act, which requires all land occupiers to control designated noxious plants if found on their property (BCMAL 2002).

As there are populations of Centaurea solstitialis in U.S. counties adjacent to B.C., it is recommended that an early detection and rapid response (EDRR) program should be employed by the province.

Table 2: Summary of types of livestock in regions of British Columbia where Centaurea solstitialis (yellow star-thistle) could establish.
Type of Animal Number of Animals Percentage of B.C. Total
Cattle and Calves355,87144%
Sheep and Lambs38,61263%
Horses and Ponies53,24649 %

Source: Statistics Canada, 2007

Note: data is based on Census Agricultural Regions and Census Divisions, some of which extend beyond hardiness zone 5.

Potential Mitigation Measures for Intentional Introduction Pathways

No intentional introduction pathways for Centaurea solstitialis were identified. Although no mitigation measures are currently required, this pathway will still be regulated under the Plant Protection Act if this species is placed on the List of Pests Regulated by Canada (CFIA 2009).

Potential Mitigation Measures for Non-intentional Introduction Pathways

Field Crops Not Intended for Propagation

Previous imports

It is unknown which grain commodities could be potentially contaminated with seed of Centaurea solstitialis, but the weed has been noted to affect cereal production.

Potential risk mitigation measures

Regulate Centaurea solstitialis as a quarantine pest under the Plant Protection Act and add this species to the List of Pests Regulated by Canada (CFIA 2009) in order to:

All risk mitigation measures for field crop commodities containing Centaurea solstitialis must be taken with consideration for requirements/measures for pests other than plants (e.g. pathogens and insects).

Trade implications

Cost-effectiveness and Feasibility

Seed

Two specimens of Centaurea solstitialis were collected in a hay field in Campbellford, Ontario in 1971, prior to the listing of this species on the Weed Seeds Order in 1986.

Previous imports

It is unknown which grain commodities could be potentially contaminated with seed of Centaurea solstitialis, but the weed has been noted to affect cereal production.

Potential risk mitigation measures

Regulatory actions under the Plant Protection Act could include one or more of the following:

Trade implications

Cost-effectiveness and Feasibility

Hay and Straw

Previous imports

Potential risk mitigation measures

Regulate Centaurea solstitialis under the Plant Protection Act as a quarantine pest by placing it on the List of Pests Regulated by Canada (CFIA 2009) in order to:

Trade implications

Cost-effectiveness and Feasibility

Livestock

Previous imports

Potential risk mitigation measures

Trade implications

Exporters are already required to undergo inspection of livestock at the border.

Cost-effectiveness and Feasibility

Vehicles and Used Farm Machinery

Previous imports

Potential Risk mitigation measures

Enforcement of the Directive 95-26: "Phytosanitary requirements of soil and related matter and for items contaminated with soil and related matter" (CFIA 2008).

In 2003, CBSA assumed responsibility for the initial import inspection services in respect to the Acts and Regulations administered by the CFIA to the extent that they are applicable at Canadian border points. The inspection of goods that may be contaminated with soil are among the responsibilities that were transferred to the CBSA in 2003. The Food, Plant and Animals Programs Section of the CBSA is currently finalizing its Standard Operating Procedures (SOP) concerning the "Inspection of Imported Goods Potentially Contaminated with Soil." This SOP provides the CBSA's Border Services Officers with formal procedures for the inspection and disposition of goods that may be contaminated with soil, including used agricultural machinery and vehicles.

Nursery Stock with Soil

There are two documented references of Centaurea solstitialis being found in gardens or landscaped areas. The references indicate that the pest plant may be introduced as an ornamental plant or as a root ball of shrubs or trees.

Previous imports

Potential Risk mitigation measures

Regulate Centaurea solstitialis under the Plant Protection Act as a quarantine pest and add it to the List of Pests Regulated by Canada in order to:

Regulatory actions could include one or more of the following:

Trade implications

Cost-effectiveness and Feasibility

Phytosanitary Certificates are currently issued by exporting countries for nursery stock and exporting countries currently comply with the phytosanitary requirements set out in D-95-26, including the pest-free area.

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