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

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Identity of Organism

Name: Persicaria perfoliata (mile-a-minute weed)

Synonym(s): Ampelygonum perfoliatum, Chylocalyx perfoliatus, Echinocaulon perfoliatum, Fagopyrum perfoliatum, Polygonum perfoliatum, Tracaulon perfoliatum, Truellum perfoliatum (Park 1986).

Engligh common names: Mile-a-minute weed, devil's-tail tearthumb, giant climbing tearthumb, mile-a-minute weed, mile-a-minute-vine, minuteweed, tearthumb, Asiatic tearthumb (Hinds and Freeman 1993; USDA-ARS 2008; USDA-NRCS 2008).

French common names: None.

Mile-a-minute weed was formerly included in the large genus Polygonum, as P. perfoliatum. However, more recently most botanists in North America have agreed that this plant should be placed in the genus Persicaria (Hinds and Freeman 2005).

Persicaria perfoliata is a rapidly growing herbaceous annual vine of the buckwheat family (Polygonaceae). It is a distinctive plant with triangular leaves, backward-curved barbs on the stems and lower leaf blades, and metallic blue, berry-like fruits. Also characteristic of this plant are cup-shaped leafy structures called ocreae encircling the nodes (Okay et al. 1997).

Persicaria perfoliata is native to temperate and tropical Asia. In the United States, it is introduced and invasive in disturbed sites, hedges, and riparian sites of 13 states, including New York (Hinds and Freeman 1993). This aggressive plant forms tangled mats that smother native herbs, shrubs, and understory trees (Weber 2003).

Organism Status

Persicaria perfoliata is not reported to occur in Canada (CFIA 2008). Based on this information, for the PRA area, P. perfoliata is considered absent with no pest records.

Current Regulatory Status

Prior to this RMD decision, Persicaria perfoliata was not regulated in Canada. It is not currently regulated at the federal level in the United States, Mexico, Peru, Brazil, or China. It is currently regulated at the state level in Alabama, Connecticut, Massachusetts, North Carolina, Ohio, Pennsylvania and South Carolina (USDA-NRCS 2009).

Probability of Entry

The main pathways of entry into Canada are unintentional, human-mediated dispersal and natural dispersal (Table 1). Based on previous experience from the United States, the most likely human-mediated pathway is the unintentional movement of seed or plants associated with nursery stock. Additional potential human-mediated pathways include contaminated vehicles, equipment, hay, mulch, soil, shoes, clothing, baggage and ornamental seed. Intentional introduction is also possible but the plant has low ornamental value. Due to the presence of P. perfoliata in nearby states, such as New York and Pennsylvania, natural range expansion is another potential pathway of introduction for this species.

Probability of Establishment

It is native to cool temperate regions of eastern Asia, where it is widely distributed (Johnson Jr. 1996; Steward 1930). It is most prominent in Japan, Korea and parts of China (Johnson Jr. 1996). It extends as far south as the Philippines and as far west as India, where it is generally found in cooler or mountainous regions (Johnson Jr. 1996).

In addition to its native range, it was introduced and established in the United States. The current distribution of P. perfoliata in North America is illustrated in Figure 1 and Figure 2. It has also been detected in Turkey (Güner 1984) and the Caribbean (Weber 2003) but its status (casual, naturalized, or invasive) is unknown. It was introduced into New Zealand, but has since been eradicated (EPPO 2008). In Canada, P. perfoliata was collected once along a roadside near Pitt Meadows, British Columbia in 1954, but did not persist (Douglas et al. 1990; Hinds and Freeman 1993).

It is considered to be hardy to United States Department of Agriculture's (USDA) Plant Hardiness Zone 6. Within Canada plant hardiness zones 6 to 8 are located along the coast of British Columbia and Vancouver Island, in extreme southern Ontario, and areas in the Maritime Provinces (Figure 3). Suitable habitats for P. perfoliata include a variety of disturbed areas and riparian areas. It prefers sunny, moist sites but can tolerate shady and dry sites as well. Within areas of climatic tolerance, availability of suitable habitats would not be a limiting factor for the establishment of P. perfoliata in Canada.

Table 1: Summary of pathways for Persicaria perfoliata Mile-a-minute weed
Type of Introduction Specific Pathways
Natural Means of Dispersal

Natural dispersal is reported to occur by water, birds, mammals and ants (Okay et al. 1997).

Of these natural means of dispersal, birds are probably the most significant long-distant disperser, followed by water, since the fruits can remain buoyant for at least a week (Okay et al. 1997).

Rate of spread in the U.S. has been approximately 500 km in several directions over 55 years (EPPO 2008), or approximately 9 km per year.

Persicaria perfoliata is present in several states adjacent to Canada, including Ohio, Pennsylvania and New York.

If the current trend continues, and includes northward expansion, the range of Persicaria perfoliata could expand into Canada within several decades.

The probability of entry of Persicaria perfoliata into Canada by natural means of dispersal appears to be high.

Intentional Introduction Intentional introduction is possible but the plant has low ornamental value.
Unintentional Introduction

Unintentional introduction pathways for Persicaria perfoliata include contaminated vehicles, equipment, hay, mulch, soil, shoes, clothing and baggage, seed (mainly ornamental) or grain contamination, and movement of seed or plants associated with nursery stock.

The probability of entry of Persicaria perfoliata into Canada association with contaminated seed and/or nursery stock, which were the means of introduction of this species into the U.S. by unintentional means appears to be high, especially in

Figure 1: Current range of Persicaria perfoliata (mile-a-minute weed) in North America

Note: States shaded green have at least one occurrence point.

Figure 1 description follows
Description for Figure 1:

This map shows the range of Persicaria perfoliata in North America indicating its presence through the use of the colour green. The states that have at least one occurrence point are shaded green they are: Oregon, New York, Pennsylvania, Ohio, West Virginia, Virginia, Maryland, New Jersey, and Delaware.

Source: USDA-NRCS 2009.

Figure 2: County-level distribution of Persicaria perfoliata (mile-a-minute weed) in the eastern United States

Figure 2 description follows
Description for Figure 2:

This map shows the northeastern region of North America demonstrating a county-level distribution Persicaria perfoliata (mile-a-minute weed). Yellow circles are used to distinguish the regions in which distribution is prevalent which is predominantly situated in the Connecticut, New Jersey, Pennsylvania, Maryland and Delaware regions. A scattered and minimal presence can be seen in New York and Massachusetts as well as Virginia and West Virginia.

Source: adapted from Hough-Goldstein et al. 2008.

Figure 3: USDA Plant Hardiness Zone 6

Note: Mile-a-minute weed is considered to be hardy to USDA Plant Hardiness Zone 6. Within Canada, it may establish in shaded areas along the coast of British Columbia and Vancouver Island, in southern Ontario, and areas in the Maritime Provinces.

Figure 3. description follows.
Description for Figure 3:

This is a map of North America showing the Plant Hardiness Zones 1 to 11 in different colours.

Probability of Spread

Persicaria perfoliata reproduces by seed. Individual plants can produce 50 to 100 seeds each. Vegetative growth is remarkably rapid, and can reach 15 cm per day. In addition to a variety of human-mediated means of dispersal, P. perfoliata is dispersed naturally by water, birds, ants, other small animals and deer. In the United States, it has spread rapidly over the past seven decades, and is now present in eleven states. The possibility of it spreading coast to coast has been raised. While some speculate that it could assume a perennial growth habit in Florida, other authors suggest the requirement of a cold stratification treatment for germination might limit the southward spread of this species. Overall, it has a moderate reproductive potential and a moderate to high seed mobility.

Potential Economic Consequences

Persicaria perfoliata is known to cause direct negative economic consequences on industries involved in the production of trees and shrubs, such as orchards, nurseries, Christmas tree plantations and regeneration sites. Plants germinate early and can quickly form a dense, prickly carpet of vegetation over seedlings and shrubs, causing defoliation, mechanical damage, and mortality. Potential indirect economic impacts include increased costs of control to a variety of sectors (e.g. transportation industry, parks and recreation, home gardeners), seed or grain contamination, decreased hay quality, and losses to the hunting and tourism industries.

Potential Environmental and Social Consequences

Persicaria perfoliata can cause reduced plant diversity by out competing and killing native understory plants including wildflowers, grasses, shrubs and saplings. Although P. perfoliata is often found in disturbed areas, it has the potential to cause species reductions in sensitive riparian areas as well. Furthermore, it may degrade food and habitat for wildlife, restrict wildlife movement, and reduce the aesthetic value of properties and public areas. The prickly vines, which can form dense thickets, are a nuisance to people, pets and wildlife.


Areas of uncertainty that were identified in the risk assessment related to the potential for P. perfoliata to establish and spread in colder climates than it has previously, and the scarcity of quantitative information on the economic impacts of this species.

Conclusion of Weed Risk Assessment

Persicaria perfoliata is an aggressive invasive plant that can cause significant economic and environmental harm. Potential mitigation measures should be considered for this plant, recognizing that over time spread by natural means from the northeastern United States into Canada might occur.

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