Japanese Wisteria (Invasive Exotic Plants of North Carolina)

Japanese Wisteria

Wisteria floribunda

Description ⁵

More info for the terms: shrub, vine, vines

This description provides characteristics that may be relevant to fire ecology and is not meant for identification. Keys for identification are available (e.g., [24]).

Both Japanese and Chinese wisteria are showy, ornamental perennial lianas that commonly climb, twine, or trail on the ground [21,34]. Chinese wisteria is also occasionally described as a shrub [8,19]. Both species have been observed 65 feet (20 m) high in the canopy [34], and there are records of vines 70 feet (21 m) long [21]. The species look similar to each other and can be difficult to distinguish because they hybridize [21,35]. One way to differentiate the species is by examining the direction of vine twining; Chinese wisteria vines twine clockwise, while Japanese wisteria vines twine counter-clockwise [22].

Roots: One flora describes Chinese wisteria roots as few but "deeply penetrating" [41].

Stems: Stems of older wisteria plants can grow 15 inches (38 cm) in diameter, and have infrequent, alternate branches [34].

Leaves: Compound leaves of wisterias are about 1 foot (0.3 m) in length and alternate along the stem. Japanese wisteria leaves consist of 13 to 19 leaflets, while Chinese wisteria leaves consist of 7 to 13 leaflets [34].

Flowers: Wisteria flowers are dangling and showy, blue-violet, and are borne on racemes. Racemes are 4 to 20 inches (10-50 cm) long and 3 to 4 inches (7-10 cm) wide. All Chinese wisteria flowers bloom at the same time, while Japanese wisteria flowers bloom in sequence, starting at the base [21].

Fruits: Wisteria fruits are velvety brown seed pods, 4 to 6 inches (10-15 cm) long, narrowed toward the base, with constrictions in the pods that separate the seeds [34]. Each pod contains 1 to 8 flat, round, brown seeds, each 0.5 to 1 inch (1.2-2.5 cm) in diameter [21].

Ecological threat in the united states ⁶

The hard woody vines of Japanese wisteria twine tightly around host tree trunks and branches and cut through the host tree bark, eventually girdling and killing it. On the ground, new vines germinating from seed or sprouting from rootstocks form dense thickets that smother and shade out native vegetation and impede natural plant community development. As girdled trees die, canopy gaps are created which increase the amount of sunlight reaching the forest floor. While this may temporarily favor some native species, it also stimulates vigorous growth and spread of wisteria.

Impacts and control ⁷

More info for the terms: cover, fire management, hardwood, invasive species, prescribed fire, presence, restoration, vine, vines

Impacts: Information regarding the impacts of wisterias on invaded communities includes evidence that both species displace existing vegetation by strangling or shading out native plants and trees [17,21,30,34,35]. The death of large trees from wisteria establishment results in breaks in closed canopy forest, which favors further growth and spread of wisteria [17]. Once established in an area, wisteria patches can potentially cover several acres; one herbicide experiment in Alabama was conducted in a Chinese wisteria patch that covered 2 to 3 acres (1 ha) [22]. The presence of Chinese wisteria was listed as a problem in the restoration of bottomland hardwood forests in Mississippi [32] and threatens old-growth remnant stands of longleaf pine in the Southeast [40]. Chinese wisteria is also listed as occurring on National Wildlife Refuges in Florida [16].

While both wisteria species are listed as invasive species of concern in a number of states, information as of 2009 suggests that they are less of a perceived threat than other, co-occurring invasive species [23,29,37,44]. For example, in a paper describing woody invaders of eastern forests, Japanese and Chinese wisteria are not considered as much of a threat as other woody vines, including Oriental bittersweet (Celastrus orbiculatus), Japanese honeysuckle (Lonicera japonica), or kudzu (Pueraria montana) [44]. However, that status may change in the future.

Control: 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 [5]. 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 wisterias in the context of fire management. For more detailed information on control of Japanese or Chinese wisteria, 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: No information is available on this topic.

Cultural: No information is available on this topic.

Physical and/or mechanical: One review outlines strategies for cutting climbing or trailing vines of Japanese wisteria. Wisteria can sprout numerous times after cutting, so the treatment must be repeated until root stores are exhausted. If done approximately every 2 weeks from spring until autumn, cutting prevents seed production and strangulation of surrounding vegetation. This type of treatment is appropriate for small populations, as a pre-treatment for large, impenetrable sites, or in areas where herbicides are not appropriate [30].

It is also possible to try to control juvenile or isolated Japanese wisteria plants using a pulaski or similar digging tool to remove the entire plant, including all roots and runners. Any portions of the root system not removed are capable of sprouting. This treatment is appropriate for small initial populations or areas where herbicide use is not feasible [30].

Biological: No information is available on this topic.

Chemical: A range of foliar spray herbicides has been effectively used for wisteria control [22,30], though high rates and repeated applications were needed to produce near-eradication [22] and it was possible to damage non-target species with treatment. Cut-stump application of glyphosate or triclopyr 2 inches (5 cm) above ground level was also found to be effective for Japanese wisteria control, though foliar spray treatments may be needed afterward to compensate for the stimulation of wisteria seedlings after large vine removal [30]. Care must be taken when other invasive species are present; in one herbicide treatment, the reduction in Chinese wisteria cover released the invasive Chinese privet (Ligustrum sinense), which was not impacted by the herbicides [22].

Integrated management: No information is available on this topic.