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European swallow-wort

Vincetoxicum rossicum

Description and biology 9

  • Plant: perennial herbaceous twining vine; sap is clear and watery, not milky.
  • Leaves: paired, dark green, shiny, margins are non-toothed, oval to elliptic with a pointed tip; 2-5 in. long; are pubescent on the margins and major veins underneath; petioles are 2-8 in. long.
  • Flowers, fruits and seeds: flower buds are ovoid to conoidal with a pointed apex, unopened petals are twisted; 5-20 flowers are produced in the axils of the leaves in small branched, clusters; flowers are 5-parted and about (5-7 mm) ¼ in. across; petals are strap-like, pink, red-brown to maroon and hairless above, flower stalks are ½-2 in. long and fuzzy; fruits are slender, smooth (hairless) seed pods, about 1½-3 in. long, usually one pair per flower; pods turn from green to light brown as they mature and split open at a ventral suture to release seeds; seeds are light to dark brown, wider towards tip, about 1/3 in. long, flattened or concave on one side and convex on the other, with a tiny membranous marginal wing a silky filament.
  • Spreads: by wind-dispersed seed.
  • Look-alikes: honeyvine (C. laeve), native to the mid-Atlantic and Southeast, has heart-shaped leaves and white flowers; black swallow-wort (C . louiseae), also non-native and invasive, has clusters of small five-petaled, star-shaped flowers about ¼ in. across that are purple to nearly black and covered with white hairs.

Ecological threat in the united states 10

Pale swallow-wort can form extensive patches that crowd out native plant species and have various impacts on native wildlife. In some instances old-field habitats occupied by goldenrods and grasses are replaced almost exclusively by swallow-wort, disrupting natural succession and completely altering the physical structure of those habitats. A New York study on grassland birds indicated that as swallow-wort cover increases, grassland bird presence declines. In a study of ground and stem-dwelling insects in Ottawa, Ontario, diversity of these insects was found to be lower in pale swallow-wort infestated areas than in non-invaded old-field sites and gall-makers and miners were completely absent. In New York, pale swallow-wort is displacing the federally listed Hart's tongue fern (Asplenium scolopendrium) at one site and poses a threat to additional populations in the state. Globally rare alvar habitats (limestone pavement barrens supporting unique plant communities) in New York are also threatened by expanding swallow-wort populations. Research indicates that pale swallow-wort modifies the soil microbial community, displacing native plant species that are adapted to the unique microbial associations of alvar.

Impacts and control 11

More info for the terms: alvar, competition, cover, density, fern, fire management, invasive species, natural, phenology, prescribed fire, root crown, shrubs


Impacts: Information regarding the impacts of black or pale swallow-wort on invaded communities includes evidence that swallow-worts may displace existing vegetation [41,42,43], threaten rare plants, and negatively impact at least one rare ecosystem. Swallow-worts are of great management concern in the globally rare alvar ecosystem of the Lower Great Lakes Basin [16,41,42,43,56,60]. Reviews note the potential replacement of the federally endangered Jessop's milkvetch (Astragalus robinsii) by black swallow-wort and Hart's-tongue fern (Asplenium scolopendrium) by pale swallow-wort [16,41,42,56,60]. Displacement of native plant species may lead to detrimental effects on host-dependant species such as the monarch butterfly [10,11,17,29,50]. Pale swallow-wort may also have a negative effect on some grassland bird species 16. It has altered soil microbial communities [25] and insect communities 19.

A stewardship report documents 2 areas in New York where pale swallow-wort populations increased from occasional patches to large stands in 50 to 100 years; one stand now covers 12 acres (5 ha) and the other 74 acres (30 ha) [43]. Similar information was not available for black swallow-wort populations as of 2009.

A fact sheet states that the sap of the pale swallow-wort causes an allergic reaction in some people [28].   European swallow-wort infestation.

Control: Control of swallow-worts is complicated by some of their life history attributes. For example, swallow-worts have very effective seed dispersal [43]; one author speculates that prevailing winds off the Great Lakes have facilitated pale swallow-wort spread in the region [60]. Land management activities may also contribute to seed dispersal for both species; mature plants and seeds may be harvested during haymaking operations and moved to new sites when the hay is transported [43] and potentially when it is consumed. Furthermore, the ability of swallow-worts to regenerate vegetatively makes control efforts difficult (see Vegetative regeneration).

In all cases where invasive species are targeted for control, the potential for other invasive species to fill their void must be considered, no matter what method is employed [6]. Information presented in the following sections may not be comprehensive and is not intended to be prescriptive in nature. It is intended to help managers understand the ecology and control of swallow-worts in the context of fire management. For more detailed information on control of black or pale swallow-wort, consult the references cited here or local extension services.

Fire: For information on the use of prescribed fire to control this species, see Fire management considerations.

Prevention: It is commonly argued that the most cost-efficient and effective method of managing invasive species is to prevent their establishment and spread by maintaining "healthy" natural communities 48,58. Managing to maintain the integrity of native plant communities and identification of the causal factors enhancing ecosystem invasibility are likely to be more effective than an emphasis on controlling the invader [30].

Prevention of swallow-wort infestations is difficult because of the wide distribution of both species and their ability to easily disperse numerous seeds via wind. Establishment of large monospecific stands may be prevented by manually removing isolated individuals and small patches before they spread, perhaps using some of the mechanical techniques [43] described in Physical and/or mechanical control.

Cultural: There is limited information on the use of cultural practices to control swallow-wort populations. In central New York, glyphosate and triclopyr herbicide application was followed by native rye grass (Elymus spp.) plantings to investigate whether rye grasses could effectively suppress pale swallow-wort. Drought conditions persisted during the study period, and the rye grasses failed to establish after germination. However, the author speculated that using species that provide early season light competition (e.g., broadleaved natives) might be an effective control strategy because swallow-worts accomplish most of their growth early in the growing season [44]. A fact sheet suggests that invasive pale swallow-wort populations might be brought under control by plowing and planting an annual crop that persisted until the pale swallow-wort seed bank was depleted, possibly as long as 5 years [42]. However, this strategy may not be feasible or appropriate in wildlands.

Physical and/or mechanical: Several physical or mechanical measures have been attempted to control swallow-worts, although these strategies have proved problematic due to the regeneration capacity of swallow-worts (see Vegetative regeneration). To date (2009), all of the research in this field comes from attempts to control pale swallow-wort populations and involves either using physical barriers to cover or smother plant populations, cutting and mowing, or digging up plants.

Using a physical barrier to cover or smother populations: On the Fletcher Wildlife Garden near Ottawa, several methods for controlling pale swallow-wort infestations were tested, with variable results. Mulching materials, including thick leaf cover, landscape cloth, or multiple layers of newspapers were used to suppress pale swallow-wort growth around the bases of trees and shrubs. Though some pale swallow-wort plants penetrated through the mulches, they occurred in much lower densities than on sites without mulch [21].

Fletcher Wildlife Garden staff also attempted smothering pale swallow-wort plants with a heavy tarp. Pretreatment density of swallow-wort was not mentioned for this study. After 1 year, some plants had grown through holes in the tarp, but no plants could be seen under intact parts of the tarp. No seedlings were visible, suggesting the tarp had prevented the germination of the previous years' seeds. Upon removal of the tarp after 2 years, only a few plants were found and were manually dug out [21].

A group called Urban Forest Associates also attempted to smother pale swallow-wort plants in an open field near Toronto. Plastic sheeting was applied to block light and appeared to effectively prevent pale swallow-wort growth while intact. However, the sheeting was repeatedly torn open by animals, which ultimately allowed pale swallow-wort to recover to pretreatment levels (Urban Forest Associates, unpublished 1996 study cited in [12]).

Cutting or mowing: Several cutting or mowing strategies have been used to control pale swallow-wort populations. In general, these programs have not succeeded because swallow-worts sprout from stem nodes or from the root crown after damage [21,43,44,45,51]. In many cases, repeated clippings or mowings were necessary, making this type of control long-term and labor-intensive [3,12,21].

In one project in Ottawa, Fletcher Wildlife Garden staff tried cutting pale swallow-wort flowerheads before seed set. However, the plants sprouted rapidly below the cut and sent up new flowerheads. Three or 4 additional cuttings were needed to prevent growth and reproduction. The group decided this treatment was impractical, especially for widespread infestations. Mowing to stop seed production and dispersal was also attempted, though the ideal time for mowing based on plant phenology coincided with bird nesting, and the treatment had to be delayed. Consequently, multiple mowings were needed [21]. Urban Forest Associates also attempted to mow pale swallow-wort plants in an open field near Toronto. Repeated mowing reduced average stem height but did not ultimately reduce cover to a "satisfactory" extent [12]. In New York, experimental plots of pale swallow-wort that were clipped in June and July had greater stem densities than unmanaged plots by September. Repeatedly clipped stems still produced seed occasionally [3]. 

Fact sheets for both species claim that mowing will not eradicate populations but can be used to prevent a seed crop if done in early to mid-July [41,42]. In one study, pale swallow-wort seedlings and mature plants were clipped at different times during the growing season near Ottawa. This study concluded that the best time for controlling population spread with a single cutting treatment was after the first fruits were produced but before fruits fully developed, on or near 26 June in the study region [51].

Digging: Digging up plants may control swallow-wort populations, though it would likely only be practical for small populations or isolated plants [45]. Because broken root crowns left on or in the ground may sprout, care must be taken to remove and dispose of the entire root crown [43,44].

See Integrated Management for projects that combine physical and mechanical techniques with other control methods.

Biological: The potential for biocontrol has not been studied for either black or pale swallow-wort. Both species appear to have few pests, diseases, or other biocontrols in North America [43]. Some reviews suggest that insect and fungal groups from the plants' native range that prey on these or other swallow-wort species should be investigated [16,43]. Biological control of invasive species has a long history that indicates many factors must be considered before using biological controls. Refer to these sources: [69,72] and the Weed Control Methods Handbook [65] for background information and important considerations for developing and implementing biological control programs.

No evidence suggests grazing can effectively control swallow-wort populations (see Palatability and/or nutritional value). Authors anecdotally observed cattle grazing on pale swallow-wort in New York; however, pale swallow-wort quickly reestablished in the pastures within a few years of cattle removal, especially where pale swallow-wort populations were present on adjacent land [16]. Similarly, another author observed that grazing cattle suppressed pale swallow-wort, but plants rebounded once pastures were abandoned. Horses avoid it, which may encourage pale swallow-wort infestation if growth from other plants is reduced [43]. Reviews state that grazing and trampling could stimulate sprouting from stem leaf axils and perennating buds on the root crown [16,43], though no data are given to support this statement.

Chemical: There has been some experimentation on the use of herbicides to control swallow-wort populations. In general, these studies suggest that chemical control alone is not effective, and long-term reapplication is needed to sustain control [12,41,42,44,45]. General guidelines for cut-stem and foliar application of chemicals are available in fact sheets for both black [41] and pale [42] swallow-wort.

In central New York, the effectiveness of foliar spray and cut-stem applications of glyphosate and triclopyr was investigated during the growing season. The chemical treatments lowered pale swallow-wort plant density, cover, and biomass compared to untreated plots, though not by the targeted 90%. Foliar spray applications were more effective than cut-stem applications. However, foliar application of herbicides may be difficult because swallow-worts twine around shrubs and trees. Reapplication would be required for long-lasting control, because a flush of pale swallow-wort seedling growth was observed after treatment. If herbicides are used, application during the reproductive stage is advised; plants treated with glyphosate aborted their flowers and made no further reproductive effort the year of treatment [44,45].

Urban Forest Associates also used herbicides on pale swallow-wort in an open field near Toronto. Repeated applications of 5% glyphosate were needed to strongly limit regrowth the following year, and living buds were found on some roots 1 year after repeated treatments. Single applications did not reduce cover satisfactorily 1 year after treatment (Urban Forest Associates, unpublished 1996 study cited in [12]).

A New York study found that pale swallow-wort plants treated with triclopyr in June did not produce seed within that growing season. After herbicide application, there was a reduction in pale swallow-wort cover and an increase in the cover of other vegetation, though most of these species were nonnatives. The authors speculate that the loss of both adult and seedling swallow-wort plants led to a reduction in light competition and likely stimulated the germination of dormant seeds of other species [3].

See Integrated Management for projects that combine chemical application with other control methods.

Integrated management: A number of sources advocate an integrated management approach to the control of black and pale swallow-wort populations [12,43,51]. However, only a few studies have combined control techniques to investigate the efficacy of integrated management.

One study in New York investigated pale swallow-wort response to 4 treatments: (1) June herbicide application, (2) June clipping, (3) June and July clipping, and (4) a combination of June herbicide application with July clipping. The study found that one application of triclopyr, regardless of clipping, suppressed pale swallow-wort populations through postapplication growing seasons 1 and 2. On chemically treated compared to untreated plots, cover was reduced by 81%, and stem density was reduced by 86%. Adding clipping to the chemical treatments resulted in no significant difference in swallow-wort cover; chemical treatment alone was as effective as the combination treatments [3]. The combination of fire with other control methods may not improve the success of control efforts (see Use of Fire as a Control Agent).

Cynanchum rossicum 12

Cynanchum rossicum is a flowering plant of the milkweed family. It is a perennial herb native to southern Europe and is a highly invasive plant growing in all of the Eastern United States, in the mid west, and southern Ontario, Quebec, and British Columbia. It has several common names including swallowwort, pale swallowwort, and dog-strangling vine.

Contents

  • 1.1Leaf Characteristics
  • 1.2Flower Characteristics
  • 1.3Root Characteristics
  • 2Reproduction
  • 3Survival
  • 4Distribution
  • 5Invasive species
  • 6References

    • Characteristics[edit]

    Leaf Characteristics[edit]

    The leaves of the pale swallowwort are larger when they are closer to the stem and decrease in size as they move away from the stem.[2] They are in the shape of an ellipse or an oval and contain smooth margins and major veins underneath.[2] The glossy, dark green leaves grow opposite on the stem and are ovate to elliptical. The flowers appear near the top of the plant and grow on stalks that come from the leaf axils.

    Flower Characteristics[edit]

    The buds of the flowers have a pointed apex and are ovoid to conoidal. Also, petals that are unopened are twisted. The diameter of the flowers is 5–7 mm and they are 5-parted.[2] Some of the petals are 3–5 mm in long and do not have hair. The margins of the petals are 0.05–0.15 mm wide and they are typically translucent.[2] The 5-lobed corona is typically pink, red-brown or maroon, which is the same color as the corolla.[2] The corona is sometimes seen as a lighter pink, orange or yellow.[2] The fruits of the Cynanchum rossicum are 4–7 cm long and each flower typically contains two fruits. The seeds of the fruit are oblong and are either concaved or flattened on one side and convex on the other side.[2] The seed color varies from light to dark brown.[2] Each stalk has 5 to 20 flowers. The flowers are dark purple or dark brown.

    Root Characteristics[edit]

    It is a twining vine that grows to heights of 60–200 cm (2.0–6.6 ft). The roots of the pale swallowwort are thick. The rootstalk makes a rhizome shape with its roots. Stems are found intertwined in dense patches of plants.[2] They will grow onto other plants when they are alone in order to have structural support.[2] After a year of growth, the stem turns light brown and resembles a decaying stem and stops growing, yet it remains to cling onto the plant.

    Reproduction[edit]

    Cynanchum rossicum reproduces by spreading its seeds through wind dispersal and through vegetative production. Since it is multiembryonic, it allows the seeds to cover more ground and allows the pale swallowwort to have a high reproductive rate.[1] Intermediate light is the best light source for the pale swallowwort to reproduce and grow.[1] Though that light is not necessarily required, it does produce the best outcome. Typically this invasive species is found in dense vegetation, which allows it to rapidly grow with its multiembryonic seeds. Since this invasive species is a vine, it grows best when it attaches to other plants and uses it as a support beam.[1]

    Survival[edit]

    These seeds are polyembryonic and typically contain two embryos but there have been observations of up to eight embryos. When there are multiple embryos released into an environment, they have a greater chance of surviving when damage is done to the environment.[3] This makes the survival rate of the pale swallowwort to be very high and in there lies the problem as to why this invasive species is problematic.[2]

    Distribution[edit]

    Cynanchum rossicum is problematic in North America. Specifically it is problematic in the Great Lakes Basin where its invasive ways are disturbing native birds and plants in the area.[4] It is a possible threat to the butterflies as well because it interferes with the native hosts present in the area. If the native species is taken over by the pale swallowwort, it may affect the butterflies that use those plants for habitats.[4] There are not any control methods that stop the Cynanchum rossicum from spreading. In Canada, the release of a moth, (Hypena opulenta), which feeds on the plant, has been authorized in 2013.[5] It keeps growing at an extremely fast rate and invading environments in North America. It is found in Michigan, Pennsylvania, southern Ontario, Missouri, Kansas, and in New York.[6]

    Invasive species[edit]

    C. rossicum is a highly invasive plant growing in all of the Eastern United States, and commonly found in the mid west. It is also found in Southern Ontario, Quebec, and British Columbia.[7] It is commonly found along with poison ivy plants.[1]

    References[edit]

    1. ^ abcdeHotchkiss, E. E.; Ditommaso, A.; Brainard, D. C.; Mohler, C. L. (2008). "Survival and performance of the invasive vine Vincetoxicum rossicum (Apocynaceae) from seeds of different embryo number under two light environments". American Journal of Botany95 (4): 447–53. doi:10.3732/ajb.95.4.447. PMID 21632369. 
    2. ^ abcdefghijkDiTommaso, Antonio; Lawlor, Frances M.; Darbyshire, Stephen J. (2005). "The Biology of Invasive Alien Plants in Canada. 2. Cynanchum Rossicum (Kleopow) Borhidi [= Vincetoxicum Rossicum (Kleopow) Barbar.] and Cynanchum Louiseae (L.) Kartesz & Gandhi [= Vincetoxicum Nigrum (L.) Moench]". Canadian Journal of Plant Science85 (1): 243–63. doi:10.4141/p03-056. 
    3. ^Megan L. Blanchard; Barney, Jacob N.; Averill, Kristine M.; Mohler, Charles L.; DiTommaso, Antonio (2010). "Does Polyembryony Confer a Competitive Advantage to the Invasive Perennial Vine Vincetoxicum Rossicum (Apocynaceae)". Journal of Botany97 (2). 
    4. ^ abVladimir V. Kircsfalusy; Miller, Gavin C. (2008). "Invasion and Distribution of Cynanchum Rossicum (Asclepiadaceae) in the Toronto Region, Canada, with Remarks on Its Taxonomy". Thaiszia Journal of Botany18: 21–36. 
    5. ^Naomi Cappuccino, associate professor, Carleton University, Ontario, Canada, as reported by the Ottawa Citizen on 2014 08 12.
    6. ^Scott E. Sheeley; Raynal, Dudley J. (1996). "The Distribution and Status of Species of Vincetoxicum in Eastern North America". Bulletin of the Torrey Botanical Club123 (2): 148–56. doi:10.2307/2996072. 
    7. ^Pale Swallowwort, Ontario Wildflowers

    Sources and Credits

    1. (c) anonymous, some rights reserved (CC BY-NC), http://www.biopix.com/photos/JCS-Vincetoxicum-rossicum-64188.JPG
    2. (c) Ashour Rehana, some rights reserved (CC BY-NC-ND), http://www.flickr.com/photos/arehana/1642331971/
    3. (c) anonymous, some rights reserved (CC BY-NC), http://www.biopix.com/photos/JCS-Vincetoxicum-rossicum-64189.JPG
    4. (c) anonymous, some rights reserved (CC BY-NC), http://www.biopix.com/photos/JCS-Vincetoxicum-rossicum-64187.JPG
    5. (c) nolieschneider, some rights reserved (CC BY-NC), uploaded by nolieschneider
    6. (c) Brittany, some rights reserved (CC BY-NC), uploaded by Brittany
    7. (c) Mike Leveille, some rights reserved (CC BY-NC), uploaded by Mike Leveille
    8. (c) Fluff Berger, some rights reserved (CC BY-SA), uploaded by Fluff Berger
    9. (c) Unknown, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/22734037
    10. (c) Unknown, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/22948603
    11. Public Domain, http://eol.org/data_objects/24628373
    12. (c) Unknown, some rights reserved (CC BY-SA), http://eol.org/data_objects/31458721

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