Bittersweet Nightshade (Invasive Exotic Plants of North Carolina)

Bittersweet Nightshade

Solanum dulcamara

Summary ⁹

Solanum dulcamara, also known as bittersweet, bittersweet nightshade, bitter nightshade, blue bindweed, Amara Dulcis,climbing nightshade, fellenwort, felonwood, poisonberry, poisonflower, scarlet berry, snakeberry,trailing bittersweet, trailing nightshade, violet bloom, or woody nightshade, is a species of vine in the potato genus Solanum, family Solanaceae. It is native to Europe and Asia, and widely naturalised elsewhere, including North America, where it is an invasive problem weed.

Distribution habitat ¹⁰

Distribution
Solanum dulcamara is widespread throughout Europe, into north Africa and across northern Asia to the northern islands of Japan.It occurs from sea level to almost 2000 metres elevation in the Alps.It is found in the India/Pakistan border region –Kashmir. It also occurs in North America and New Zealand, where it has been introduced from Europe.

Habitat
Solanum dulcamara is normally found in open areas, for example

along streams
in clearings
on sea shores
at roadsides

It thrives in disturbed soil and can regenerate from small pieces of stem left in the ground.Seaside forms of S. dulcamara tend to be prostrate - flattened - with small, thick, leathery leaves.Plants growing in swampy places with lots of water have larger leaves, and root along the stems.

Impacts and control ¹¹

More info for the terms: cover, invasive species, natural, shrubs

Impacts: A review indicated that bittersweet nightshade was typically not abundant or aggressive enough to require control [53]. The Nature Conservancy has given bittersweet nightshade a national ranking of "low" based on its overall low ecological impacts, but they are moderately concerned about its widespread distribution and abundance [126].

Bittersweet nightshade likely poses the greatest threat in portions of North America where it is most common (see General distribution), especially in riparian communities where it is most likely to be abundant (see Population structure and Site characteristics) ([46], reviews by [93,125,126]). On sites where it is abundant, bittersweet nightshade's ability to grow over trees and shrubs may cause changes in community structure (reviews by [93,117,126]) and, to a lesser extent, composition (review by [126]). In Oregon, Fierke and others [46] suggested that dense homogenous patches of bittersweet nightshade may inhibit germination and establishment of native plants. They further speculated that invasive species such as bittersweet nightshade may be a threat to successional development in cottonwood riparian forests.

In Oregon, bittersweet nightshade is ranked as "moderately invasive" in wetlands and riparian areas. Weeds with this ranking moderately impact native habitats but likely do not cause native plant or invertebrate extirpations [125]. An analysis of invasive plant survey data from the upper Great Lakes states ranked invasive species on their ability to invade natural plant communities. Bittersweet nightshade was given a 3.3 ranking on a scale of 0 to 10 (0 = little or no ecological impact, 10 = invades and replaces native plant communities) [136]. Field records from New England indicate that bittersweet nightshade typically occurs as a single plant or in small patches (1 to 20 plants) that comprise 5% or less of the overall vegetation cover. Larger populations (20-99 plants) of bittersweet nightshade occasionally occur, and on one site bittersweet nightshade cover was greater than 25% [117].

Bittersweet nightshade occurs in non-riparian sites; however, information pertaining to its invasiveness in these communities is limited. Although it occurs in non-riparian deciduous forest communities in eastern North America, available literature suggests that its abundance may decline or remain steady over time [79,85]. In the Great Lakes region, bittersweet nightshade is considered a "lesser invader" of forests and wetlands (review by [28]). Smith [150] speculated that bittersweet nightshade may not persist on dry sites over time, suggesting that its impacts in non-riparian areas may not be long-lasting (see Successional status).

Information pertaining to bittersweet nightshade's invasiveness in portions of North America where it is less common is limited and may indicate that its impacts are less severe in these areas. In Utah and the Great Plains, bittersweet nightshade is "rarely encountered" [64,174], in Colorado it was collected in only 1 drainage [172], and in North Carolina, bittersweet nightshade is rare and typically occurs in the mountains [134]. Although some of these reports are dated, a national invasive species database [126] indicates that bittersweet nightshade has not become more of a threat in these areas in recent times. Its ability to grow in warm climates suggests that it may continue to spread to other areas in the south (e.g. into Arkansas) (review by [126]).

In the Netherlands, bittersweet nightshade may be an alternative host for late blight (Phytophthora infestans), a pathogen that negatively impacts agricultural crops in the Solanaceae family. Infection in bittersweet nightshade, however, appears to be uncommon [49]. Control: Control of invasive plant species is most effective when it employs a long-term, ecosystem-wide strategy rather than a tactical approach focused on battling individual invaders [110]. Numerous methods have been suggested to control the spread of bittersweet nightshade, but information pertaining to their effectiveness in wildlands is limited. Regardless of the control method employed, removal of moderate to large infestations of bittersweet nightshade should be followed by replanting with desirable species to minimize reinvasion by bittersweet nightshade or other weeds. All treatments should be followed by monitoring for several years to help identify further infestations and determine survival of planted material (review by [93]). Prevention: Early detection followed by immediate eradication helps to prevent the spread of many invasive plant species. Small infestations of bittersweet nightshade are easy to identify from mid-May to late fall, when it is flowering or fruiting. Manual control of new infestations and subsequent site monitoring may help prevent initial infestations from spreading (review by [93]).

Occasionally, bittersweet nightshade is still cultivated (review by [126]). Discouraging its commercial distribution and deliberate planting may help to prevent accidental introduction into native habitats.

Integrated management: Integrated management focuses not only on eradicating the target plant but also on establishing desirable species and maintaining weed-free systems over the long term. The King County Noxious Weed Control Program in Washington (review by [93]) recommends integrated management to maximize control of bittersweet nightshade and minimize negative impacts to the site. For large infestations, bittersweet nightshade can be cut with loppers or brushed mowed, followed by digging up roots or spot-spraying any remaining growth with an appropriate herbicide. As an alternative to herbicide, remaining growth can be covered with a heavy duty fabric to suppress further growth (review by [93]).

Physical or mechanical control: Bittersweet nightshade may be controlled manually by pulling or digging up the roots, which is easier when the ground is wet or loose (reviews by [28,53,59,93]). This method is most effective with young plants or new infestations (review by [93]). Care must be taken not to break the rhizomes or roots because fragments may regenerate vegetatively ([58,89], reviews by [93,183]).

Other physical or mechanical methods of control include repeat cutting or covering plants with a weed barrier (review by [93]). In a field in New York, however, repeat mowing failed to eliminate woody plant species including bittersweet nightshade [167].

Fire: See Fire Management Considerations.

Biological control: There are currently no biological control agents available for bittersweet nightshade (review by [93]).

Chemical control: Bittersweet nightshade may be controlled with selective broadleaf or broad-spectrum herbicides (reviews by [53,93]) but to what extent is uncertain. Following herbicide treatment, bittersweet nightshade should not be cut back until foliage turns brown or is dead (review by [93]). Several applications in the same year or consecutive years may be necessary for adequate control ([40], review by [93]). A few publications provide information on potential chemical treatments ([38,39,40], review by [93]). See The Nature Conservancy's Weed Control Method Handbook [161] for information on specific chemicals and how to correctly use herbicide in wildlands. Only herbicides approved for use in and near water can be used to control bittersweet nightshade infestations in riparian areas and other habitats adjacent to water. To prevent damage to desirable species, herbicide application should be done before other plants emerge or after they have gone dormant (review by [93]). For most weeds, herbicides are effective in gaining initial control of a new invasion or a severe infestation, but they are rarely a complete or long-term solution to weed management [20].

A 1919 review suggests that pouring hot brine or caustic soda around the roots will control bittersweet nightshade [59].

Cultural control: No information is available on this topic.

Sources and Credits

(c) Dietmut Teijgeman-Hansen, some rights reserved (CC BY-NC-ND), https://www.flickr.com/photos/reisgekki/6108646608/
(c) Giuseppe Quattrone, some rights reserved (CC BY-NC-ND), http://www.flickr.com/photos/14957129@N04/3622151271
(c) José María Escolano, some rights reserved (CC BY-NC-SA), http://farm5.static.flickr.com/4121/4760155578_182bc8de9f.jpg
(c) Phil Sellens, some rights reserved (CC BY), http://farm3.staticflickr.com/2483/3907493402_4a3965db12_o.jpg
(c) José María Escolano, some rights reserved (CC BY-NC-SA), http://farm5.static.flickr.com/4100/4760154510_b55563ec73.jpg
(c) Guido Gerding, some rights reserved (CC BY-SA), https://upload.wikimedia.org/wikipedia/commons/0/05/XN_Solanum_dulcamara_01.jpg
(c) MPF, some rights reserved (CC BY-SA), https://upload.wikimedia.org/wikipedia/commons/0/0c/Bittersweet_Solanum_dulcamara_Big_Waters_2.jpg
(c) H. Zell, some rights reserved (CC BY-SA), https://upload.wikimedia.org/wikipedia/commons/b/b5/Solanum_dulcamara_0002.JPG
Adapted by Kate Wagner from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Solanum_dulcamara
(c) Natural History Museum, London, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/12496846
Public Domain, http://eol.org/data_objects/24639420

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