RMD-13-04: Consolidated Pest Risk Management Document for pest plants regulated by Canada
Appendix 11B: Risk Management Considerations for Persicaria perfoliata (mile-a-minute weed)

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Pest Management

Persicaria perfoliata can be effectively controlled with herbicides either preemergence or postemergence (McCormick and Hartwig 1995). Hand-pulling, cultivation, and herbicides can control P. perfoliata on small scales; however, these methods are not feasible for large infestations or infestations in environmentally sensitive areas (Mountain 1989; Hough-Goldstein and Lake 2008; Price et al. 2003). Mechanical control is ineffective (Lehtonen 1994). The seed remains viable in the in the soil for six years, so managing P. perfoliata successfully depends on yearly treatments (Hough-Goldstein et al. 2008). A classical biological control program for P. perfoliata began in the U.S. in 1996 (Hough-Goldstein et al. 2008) using the weevil Rhinoncomimus latipes, a natural enemy introduced from China which is specific to the vine; with releases beginning in 2004 (Hough-Goldstein and Lake 2008; Hough-Goldstein 2008; Colpetzer et al. 2004).

Pest Risk Assessments from Other Countries

A pest risk assessment has been conducted by USDA-APHIS (Lehtonen 1994). The overall pest risk potential rating in the USDA-APHIS assessment was "high", which was based on "high" ratings for spread probability and environmental impact potential, and a "medium" rating for economic consequences of establishment. It was determined that the species no longer met the definition of noxious weed as required for listing under the U.S. Federal Noxious Weed Act. Recommendations included investigation of biological control for the species and cooperation in integrated management with other government agencies willing to share costs of control.

A Report of a Pest Risk Analysis on Polygonum perfoliatum is available from EPPO (EPPO 2007). The overall conclusion of pest risk assessment portion of the analysis was that the risk is unacceptable and management measures should be considered; it also reported that the plant is capable of causing significant damage to freshwater ecosystems and to commercial forest areas and forest regeneration. The report identified plants for planting with growing media, soil as a commodity, and imports of Meliosma seeds as the main introduction pathways.

New York State (U.S.) completed a non-native plant invasiveness ranking form for P. perfoliata concluding an invasiveness rank of "very high".

Existing Domestic, Provincial or other Programs

There are no existing Canadian programs related to the management or control of P. perfoliata . A Mile-A-Minute Control Management Plan has been developed by the Pennsylvania Department of Agriculture where the plant is a State Noxious Weed; it is a joint control program between the USDA-APHIS PPQ and the Pennsylvania Department of Agriculture (Bravo 2008). Persicaria perfoliata is considered widely distributed in the U.S. so does not meet the definition of a noxious weed as required for listing under the Federal Noxious Weed Act; eradication is no longer feasible (Lehtonen 1994). At the U.S. State level, it is listed as a Class A noxious weed in North Carolina, a prohibited noxious weed in Ohio, and a noxious weed in Pennsylvania and Alabama (Kumar and Ditommaso 2005).

Persicaria perfoliata can unintentionally contaminate hay (Castro 2008). Weed free forage programs can help prevent the spread of invasive plants. The Government of Alberta, Agriculture and Rural Development, administers the Alberta Certified Weed Free Hay Program. The objectives of the program are to provide a premium product that is recognized as marketable and transportable, to prevent the spread of restricted and noxious weeds, and to protect private and public lands from non-native, invasive plant species. Persicaria perfoliata is not currently designated as an undesirable plant on this list.

Canadian Christmas Tree Industry

Persicaria perfoliata is known to have deleterious economic consequences on the production of Christmas trees (Castro 2008). It grows rapidly and may out-compete Christmas tree seedlings. In 2007, Canada exported 2.5 million Christmas trees worth $29.8 million (Table 1). Areas in the Maritime Provinces that export Christmas trees, and that have suitable climate conditions for P. perfoliata (see Appendix 11A, Figure 3), are at risk if P. perfoliata establishes in Canada.

Potential Mitigation Measures for Natural Dispersal Pathways

Natural range expansion is a potential pathway of introduction. Persicaria perfoliata produces numerous fruits and has a high rate of seed set that contributes to natural dispersal (Oliver 1996). Once established, it can spread into surrounding habitats and watersheds by birds, animals and water (Lehtonen 1994). Birds and rodents disperse seeds as dorivers and streams, especially after flooding events (Mountain 1989; Gerlach Okay et. al 2007). Birds are also recognized as long-distance dispersal agents and ant species transport seed short distances (Kumar and Ditommaso 2005; Gerlach Okay et. al 2007). Seeds can pass through avian digestive tracts and remain viable (Okay 1997 in Kumar and Ditommaso 2005). Persicaria perfoliata seed dispersal and germination can also be facilitated by white-tailed deer (Odocoileus virginianus) (Hough-Goldstein et al. 2008). Once established in a new location, new populations can establish as P. perfoliata can reproduce without cross-pollination (Kumar and Ditommaso 2005).

Risk management of natural dispersal events is difficult. However, regulation will require surveys that would detect any new incursions established through natural dispersal pathways. Education and outreach programs, as well as pest identification training for inspectors, would also support the early detection and rapid response to new pest incursions that may result from natural dispersal events.

Table 2: Summary of Christmas trees exported by Canadian provinc and year

Value $ million
Province 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007
Nova Scotia9.49.09.611.011.19.910.810.910.68.5
New Brunswick5.
Other provinces2.

Source: AAFC 2008

Recommended Mitigation Measures for Intentional and Unintentional Introduction Pathways

Recommended risk mitigation measures

Regulatory measures under the Plant Protection Act

It is recommended that Canadaregulate P. perfloliata as a quarantine pest under the Plant Protection Act (1990, c.22)Footnote 1, and add this species to the List of Pests Regulated by Canada (CFIA 2009). This would prevent the intentional importation, movement, or cultivation of this species in Canada. The CFIA would not approve Permit to Import applications for P. perfoliata.

The CFIA would need to rescind any Permits to Import issued for Persicaria perfoliata. Any plants of Persicaria perfoliata established either outside of cultivation or in cultivation would need to be placed under official control.

To support regulation, a general requirement would be that importers would be required to provide full scientific names on all applications for Permits to Import as there are many species in the Persicaria genus.

Regulatory exemptions for the import of live or dried Persicaria perfoliata plant parts for special purposes such as research, food or medicine would be considered on a case by case basis by the CFIA.

Regulatory measures under the Seeds Act

It is recommended that Canada regulate P. perfoliata as a Class 1 Prohibited Noxious weed under the Weeds Seeds Order (SOR/2005-220) of the Seeds Act (R.S., 1985, c. S-8) Footnote 2. This species meets the definition for Class 1Footnote 3 species under the Weeds Seeds Order. All imported and domestic seed lots must be free of prohibited noxious weed seeds. Imported seed lots would require a certificate of analysis stating P.. perfoliata is absent from the seed lot before it can be imported.

The Weed Seeds Orderis a Ministerial Order made under the Seeds Act. The Weed Seeds Order allows the Minister of Agriculture and Agri-Food to regulate the seeds of the species of plants set out in the schedule that are deemed to be weed seeds for the purpose of establishing grades under the Seeds Act.

Non-regulatory measures

Education and awareness programs that foster awareness and support regulation of P. perfoliata are recommended. These would support regulatory measures, as well as prevention and early detection activities. Industry could also implement voluntary measures to end the sale and distribution of known invasive plants through mail order catalogs or internet sales.

Trade Implications

Plant Protection Act

The regulation of P. perfoliata under the Plant Protection Act will have trade impacts as commodities will need to be certified as free from the pest and subjected to new plant import requirements for import to Canada. International trade as a plant for planting is limited as it is not known to have any economic value in Canada and most countries recognize P. perfoliata as an invasive plant (Oliver 1996).

Seeds Act

The regulation of P. perfoliata under the Seeds Act will impact trade as exporting countries will need to devote resources towards inspection of seed lots and issuance of foreign Phytosanitary Certificates under the Plant Protection Act. Laboratories in exporting countries will need to be able to identify seeds of P. perfoliata within a seed sample. Exporters would need to ensure freedom of P. perfoliata in seed lots, otherwise the CFIA will refuse entry.

Cost-effectiveness and Feasibility

Additional resources would be required so that the CFIA could "trace-back" all existing permits issued for Persicariaspp. to determine if the species, P. perfoliata, has been intentionally imported. If it has been imported, an official control program would be required.

Resources would be required to expand the CFIA survey efforts. Minor costs may be incurred for pest identification training for inspectors and survey staff.

Resources would be required for an education and awareness program to foster awareness of P. perfoliata as an invasive plant and potential quarantine pest, targeting the general public, gardeners and the horticultural industry.

The CFIA currently requires import declarations and certificates of analysis for seed imported into CanadaFootnote 4. Additional resources required to regulate P. perfoliata via the seed pathway would be minimal.

Resources will be required to expand CFIA seed sampling efforts and minor costs would be incurred for seed identification training for inspectors. Seeds consist of spherical, shiny-black achenes, covered by a white or pink perianth, which becomes blue and fleshy when mature. They form blueberry-like "fruits", each 5 mm in diameter, arranged in clusters (Wu et al. 2002). Inspectors will need to be able to detect the seeds in any imported commodities.

The horticultural industry would need to be trained to recognize the seed and plants of P. perfoliata, as part of a preventive approach. The CFIA Seed Program is already in place to prevent the entry of prohibited noxious weeds. The CFIA monitors compliance with the Canadian standards through the Marketplace Monitoring ProgramFootnote 5.

Exporting countries will need to devote resources towards inspection of hay and straw commodities and for the issuance of Phytosanitary Certificates. Inspectors in foreign countries need to be able to identify seeds and plants of P. perfoliata that could attach themselves to hay and straw or that might become tangled up in the hay or straw with viable seeds attached. Exporting countries would need to ensure freedom of P. perfoliata in hay and straw, otherwise the CFIA will refuse entry.

Inspection staff at Canada Border Services Agency (CBSA) would need to be trained on how to identify P. perfoliata seed on vehicles or other equipment entering Canada. Inspections should focus on any vehicles or equipment entering Canada from infested north eastern U.S. States (see see Appendix 11A, Figure 2).

Implicated Pathways

Intentional Introduction Pathways

Plants for Planting
Plants for planting is recognized as a potential pathway of entry for P. perfoliata into Canada, however, the plant has low ornamental value (Castro 2008). Persicariaspp.have been imported intentionally into Canada. Between 2006 and 2009, the CFIA issued 25 Permits to Import for Persicariaspp., and another 11 Permits to Import permits between 2004 and 2005. However, it is not known if P. perfoliata has specifically been imported into Canada as species level data was not specified on the import permits. Permits to import Persicaria spp. have been issued to importers in Quebec (imports from the Netherlands, France, Japan, and United Kingdom), Ontario (imports from the Netherlands, United Kingdom, United States), Manitoba (imports from the Netherlands), Alberta (imports from the Netherlands) and British Columbia (imports from the Netherlands).
It is unlikely that importers would import pure lots of P. perfoliata seed. However, persons wishing to intentionally import the species may choose the seed pathway. Persicaria perfoliata could also enter Canada undetected in packets of ornamental seed, such as in wildflower mixes (Castro 2008).

Unintentional Introduction Pathways

Movement of seed or plants associated with nursery stock
A potential unintentional pathway is the importation of nursery stock or plants contaminated with seeds or plant material of P. perfoliata . The plant is well adapted for dispersal from nursery to nursery or nursery to planting-bed (Hill et al. 1981). Seeds are likely to survive along the nursery stock pathway (Castro 2008). Persicaria perfoliata seed or plants associated with nursery stock rooted in soil is a potential pathway only from the U.S. (Castro 2008). Introduction into Canada through contaminated seed commodities is a possibility (Castro 2008). Persicaria perfoliata has been reported to be unintentionally introduced by seed associated with Meliosma seed imported into the U.S. from China, and in Ilex seeds from Japan (Lehtonen 1994) as well as being reported as a contaminant from rhododendron nursery stock imported from eastern Asia (Hill et al. 1981). Seeds can remain viable for up to seven years and withstand a fairly wide range of temperatures (Castro 2008).
It is not known if nursery stock contaminated by seed or plants of P. perfoliata has been imported into Canada. The Seed Science and Technology Section of the CFIA Saskatoon laboratory maintains a record of contaminants found in domestic and imported seed. Persicaria perfoliata has not previously been detected as a seed contaminant.
Persicaria perfoliata seed may contaminate imported nursery stock present either in the soil or adhering to plants (e.g., Persicaria perfoliata can wrap around the nursery stock and fruits are known to remain on the plants long after the plant senesces) (Kumar and Di Tommaso 2005). The import of plants with soil and related matter is prohibited with the exception of shipments from the continental United States which require a Phytosanitary Certificate (see CFIA Policy Directive D-02-02 Plant protection import requirements for rooted, or unrooted plants, plant parts, and plants in vitrofor planting). Shipments of plants rooted in soil or related matter, or without soil, would be required to be free of P. perfoliata.
Hay and Straw
Hay is a potential pathway for the introduction of P. perfoliata , although there is little information about it in the literature (Castro 2008). The forage industry is economically significant in Canada (Table 2a & 2b). It is not known if P. perfoliata has been unintentionally imported into Canada as a contaminant in hay or straw (i.e., forage crops).

Summary of forage imports and exports into and out of Canada between 2003 and 2007

Table 2a: Imports
Year Quantity
('000) Tonnes
('000 Cdn$)
Table 2b: Exports
Year Quantity
('000) Tonnes
('000 Cdn$)

Source: Statistics Canada 2008

Vehicles and Equipment - Persicaria perfoliata may unintentionally be introduced into Canada as a contaminant on railroad cars, vehicles, and similar equipment (e.g. mowing equipment) entering Canada from infested areas. For example, P. perfoliata may have been introduced into Virginia (U.S.) as a contaminant of railroad cars or in mud on gas well drilling equipment (Lehtonen 1994). It can also be dispersed by logging equipment (McCormick and Hartwig 1995) and roadside mowers (Oliver 1996).

In 2003, CBSA assumed responsibility for the initial import inspection services in respect of the Acts and Regulations administered by the CFIA to the extent that they are applicable at Canadian border points. The inspections 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.

Regulatory measures would include enforcement of CFIA's Policy Directive 95-26 (CFIA 2008) that specifies the phytosanitary requirements for the import and domestic movement of soil and related matter. It includes requirements for soil and related matter individually or in association with plants, plant material, and other things such as vehicles, equipment, seed, hay, and containers. This directive also specifies the standards by which the Canadian Food Inspection Agency or the Canada Border Services Agency may inspect, certify or release these articles. If added to the List of Pests Regulated by Canada (CFIA 2009), things such as vehicles, equipment, and containers may be refused entry into Canada if contaminated with Persicaria perfoliata.

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