Introduction:
Climbing milkweed (Cynanchum rossicum)
Cynanchum rossicum is a perennial vine native to Eastern Europe that has established invasive populations in Canada and the USA. Once established, dense monocultures of the plants displace native vegetation, alter habitats, and reduce biodiversity. In particular, C. rossicum threatens rare and vulnerable alvar ecosystems in the Lower Great Lakes Basin. The species also invades and negatively impacts Christmas tree farms, horticulture nurseries and orchards, and perennial agriculture such as no-till corn and soybean fields. Successful management of the species has proven difficult, as the use of chemical controls or mechanical removal methods must be repeated annually for several years. However, a potential biological control agent, Hypena opulenta, is currently being evaluated.
Description:
Cynanchum rossicum is a perennial, herbaceous vine. Plants have horizontal, woody rootstalks that form short rhizomes, with abundant pale, fleshy, lateral fibrous roots. Stems are more or less erect, but as plants mature they twine around grasses, each other, or trees for support. Stems are also pubescent in longitudinal bands, and typically reach 60-200 cm, though especially in shaded forest understories plants can grow two to three times this length. Leaves are generally 7–12 cm long and 5–7 cm wide, ovate to elliptical, acute at the tip, and have smooth margins with occasional pubescence. They are arranged oppositely, with the largest leaves occurring in the middle of the stem. Flowers are five-petaled, star-shaped, about 5–7 mm in diameter, and are borne in clusters. The corolla is light pink, reddish brown, or maroon. The fleshy corona is distinctly 5-lobed with the lobes united only at the base, and is slightly darker than the corolla. Fruits are slender, tapered follicles, about 4-7 cm long, and usually form two per flower. The seeds are light to dark brown, obovoid to oblong, may measure 4–6.5 × 2.4–3.1 mm, and have a membranous marginal wing with an apical tuft of hairs . The species twining habit and opposite, glabrous, shiny leaves distinguish C. rossicum from other native and introduced species in the north-eastern US and adjacent regions of Canada.
Occurs in:
Agricultural areas, natural forests, planted forests, range/grasslands, riparian zones, ruderal/disturbed, scrub/shrublands, urban areas, wetlands.
Distribution Map:
Climbing milkweed (Cynanchum rossicum) Distribution in North America shown in green.
Habitat description:
Cynanchum rossicum occurs in temperate climates in North America and Eurasia. It has been reported on the edges of alluvial woods, railroad embankments, fencerows, and maple, beech, oak and ash forests in Ontario and western Quebec, and gardens, grassy slopes, and streambanks in southern Ontario. Other recorded habitats include grasslands, such as verges, lawns, old fields, etc., pastures, hedgerows, and gardens. In New York State, it occurs in a variety of habitats , including: calcareous shoreline
Close up of Climbing milkweed (Cynanchum rossicum)
outcroppings, cliffs, talus slopes, barrens and woodlands; successional old fields, shrublands and forest openings; riverside sand and gravel bars; mesic maple-basswood forests; pasturelands and crop fields; conifer plantations; limestone quarries and dredge spoils; as well as disturbed sites. C. rossicum establishes in full sun or under forest canopies, and while plants may form monospecific stands in all light conditions, growth and fecundity are normally higher in open fields or forest gaps. Plants will tolerate a wide variety of substrates, including silty and sandy loams, glacial till, deep loams, or rocky/gravelly soils, but prefer shallow, calcareous soils. In its introduced range, the distribution of C. rossicum normally includes temperature ranges in the winter of -11 to 0.7°C and in the summer of 20.7–26.4°C, with mean annual precipitation levels of 776–1,206 mm. A mean soil pH of 6.7 at a shaded site and 7.0 at an open site has been observed for C. rossicum. Research has indicated that generally emergence and establishment of C. rossicum is higher at the upper extent of this range of pH levels.
Management information:
Management of Cynanchum rossicum has proven difficult. Triclopyr and glyphosate have demonstrated effective control when applied as post-emergence foliar spray and cut-stem applications. Both methods require annual follow-up applications, and adequate control will likely be achieved only with 2-3 years of treatments. Mowing can contain invasive populations of pale swallow-wort, particularly when timed to suppress seed production, but again treatments must be repeated both within a growing season and likely for several subsequent year. Additionally, there is some evidence that C. rossicum leaves may leach allelopathic compounds as they decay that can inhibit the germination and growth of species in the soil seedbank.
The noctuid moth Hypena opulenta was discovered feeding on C. rossicum in Ukraine and is being investigated as a potential biological control agent. H. opulenta adults and larvae feed on C. rossicum, and studies have found that releases decreased reproductive output (specifically flower, seedpod, and seed production) in C. rossicum.
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