Persicaria perfoliata (mile-a-minute weed)

Water is an important mode for dispersal of P.perfoliata fruits and seeds in stream and river environments.

P. perfoliata seeds can be primarily dispersed by birds, wild animals such as chipmunks, squirrels and deer. Ants may help to carry seeds and play an important role in the survival and germination of the seeds (NPS, 2009).

In 1946 P.perfoliata was first found to establish a population at the Gable Nursery in Stewartstown, Pennsylvania, in the USA (Moul, 1948; Hill et al., 1981), where the seeds were likely unintentionally transported via rhododendron nursery stock imported from eastern Asia in the1930s (Riefner, 1982; Okay, 1997).

Little information is available on the genetics of P.perfoliata. Recent studies found that invasive North American P. perfoliata plants have lower tannin content, but exhibit higher prickle density on the node and leaf, compared with plants from native Asian populations, indicating potential evolutionary change of the plant chemical and physical defences (Jianqing Ding, Chinese Academy of Sciences, China, personal observation, 2009).

P. perfoliata is primarily a self-pollinated species with occasional outcrossing. The plant does not require pollinators for fruit and seed development (Okay, 1997). A single plant may produce 7-40 seeds per year (Hyatt and Araki, 2006), over a long season, from June until October. Fruits ripen from late June until October in Virginia, but a slightly shorter season occurs in the northeastern USA (Hill et al. 1981; Okay 1997). The plant senesces after the first frost in late October or early November in the northeastern USA (Kumar and DiTommaso, 2005). Cold stratification is usually required for breaking dormancy of achenes (Johnson, 1996; Okay, 1997; Colpetzer and Hough-Goldstein, 2004.). Germination occurs in early to mid-March and continues through April (McCormick and Johnson, 1997; Wu et al., 2002). Seeds may be viable 3 years after being buried in soil although the germination level is significantly decreased (Van Clef and Stiles, 2001).

P. perfoliata is found growing in combination with many woody and herbaceous species, and has a range of other faunal associations in its native China (Ding et al., 2004), Japan (Miura et al., 2008) and invasive range (Wheeler and Mengel, 1984; Hough-Goldstein et al., 2008a).

P. perfoliata is commonly found from cold northeastern China to south, tropical Asia, thus is able to tolerate a wide range of temperatures. Although the plant prefers open fields, it can also be found in some shaded habitats. It adapts well to a broad moisture condition, although the plant prefers growing along wet habitats. Annual rainfall in its natural habitat in China varies from about 500 to 2000 mm. In China, the plant occurs at elevations of 80 – 2300 m (Zheng et al., 2005).

In its native Asia P.perfoliata has been used as an herbal medicine for over 300 years (He et al., 1984; Yang and Kim, 1993), or as an edible wild fruit (He et al., 1984). Two protein kinase C inhibitors (PKC), vanicosides A and B, five diferuloyl esters of sucrose, and feruloylsucroses have been isolated from the plants (Sun, 1999; Sun et al., 2000), showing potential for use in medicine such as anticancer agents (Sun, 1999; Boadi et al., 2003; Pietruck et al., 2003). Nine components were recently isolated from the methanol extract of the plant and evaluated for their antioxidant activity, among which, alpha-tocopherol and methyl trans-ferulate showed significant effects (Chang et al., 2008). In addition, five phenolic acids, caffeic acid, p-coumaric acid, p-hydroxybenzoic acid, protocatechuic acid, and vanillic acid were isolated from the aqueous extracts of the plant (Chang et al., 2008; Jin et al., 2009). They are allelopathic substances that have potential in controlling crop weeds (Chang et al., 2008).

In its native Asia, P.perfoliata is valuable because it may be used in herbal medicine.

As P.perfoliata seeds or seedlings may be unintentionally introduced with other plant materials, such as nursery stock, strict quarantine is essential. P.perfoliata is easily distinguished from its relatives by the vine-like stem, triangular leaves, sharp downward curving spines on stems, and petioles, and saucer-shaped ocrea. Early detection and inspection should be conducted to remove any introduced individuals.

Many publications are available in the northeastern USA to inform land owners regarding detection and control of P.perfoliata (Binion, 2005; NPS, 2009).

In the USA P.perfoliata did not establish permanent populations in Portland, Oregon in 1890 and Beltsville, Maryland in 1937, nor in British Columbia, Canada in 1954 (Hill et al., 1981; Oliver and Coile, 1994). The plant was recently eradicated from Auckland, New Zealand (NZBI, 2009).

Maintaining vegetative community stability and broad vegetative buffers along streams and forest edges will help to shade out and prevent P.perfoliata establishment (NPS, 2009).

For the small seedlings covering ground, repeated mowing will suppress the plants and prevent or reduce flowering. However, mechanical control may not be applied for the bigger plants of P.perfoliata that climb on and cover trees.

Hand pulling is feasible and effective for removing seedlings that have less recurved barbs on the stem and leaves. However, for the bigger plants of P.perfoliata, wearing thick gloves, long trousers and a long-sleeved shirt will help prevent skin abrasion (NPS, 2009).

A biological control programme was initiated by the USDA Forest Service in collaboration with China in 1995, to screen potential host-specific natural enemies in its native Asia. A geometrid, moth, Timandra griseata, was firstly introduced from China to the quarantine in the USA, but it was rejected for the use in biological control as host range tests indicated it had a broad host range in Polygonaceae (Price et al., 2003). The Asian weevil, Rhinoncomimus latipes, was considered a promising biological control agent as it is a host-specific insect (Colpetzer et al., 2004). In 2004 this weevil was approved for release in the USA and has now established populations in Delaware, New Jersey, New York and Connecticut. By the end of 2007 more than 53,000 weevils had been reared in New Jersey and released, mostly in New Jersey, but also in Delaware, Maryland, Pennsylvania, and West Virginia (Hough-Goldstein et al., 2009), establishing populations at 63 out of 65 sites (96.9%) where they were released between 2004 and 2007. Population monitoring by Hough-Goldstein et al. (2009) also found the weevils at 30 additional non-release sites in New Jersey. They dispersed at an average rate of 4.3 km/year. Results of a 2-year impact study in field cages suggest that R. latipes feeding on P. perfoliata has the potential to impact plant growth and reproduction, thus may help to decrease plant competitive ability (Hough-Goldstein et al., 2008b). For latest summary, see Anon (2011).

Systemic herbicides like glyphosate-based products such as Roundup Classic® for upland areas and Rodeo® for wetland applications are effective (NPS, 2009).