Wisteria floribunda (Willd.) DC; Wisteria sinensis (Sims) DC (Family: Fabaceae)
Also known as: Japanese wisteria or Chinese wisteria
Wisteria is a deciduous ornamental vine that climbs trees high into the canopy, up to 60 feet. It can survive for 50 years or more and its growth is apparently limited only by the height of the trees. Wisteria can disfigure or kill desirable trees, and its leaves, fruits, and seeds are toxic to humans and many species of wildlife. Two varieties, along with their hybrids, are found in the United States: Japanese wisteria and Chinese wisteria. Japanese wisteria vines twine clockwise around host trees, while Chinese wisteria vines twine counter-clockwise. Otherwise, Japanese and Chinese wisteria have similar biological characteristics and control options.
Origin: As their common names imply, Japanese wisteria is native to Japan, while Chinese wisteria is native to China. Both were introduced to North America around 1830 as exotic ornamentals. Since that time, wisteria has been grown extensively in the southern U.S. as a decorative addition to porches, gazebos, walls, and gardens. Most infestations in natural areas are a result of escapes from landscape plantings.
Young wisteria stems are slender, brown, and densely pubescent, becoming smooth with age and developing tight gray to white bark. Older plants can grow to 15 inches in diameter.
Leaves are alternately arranged and pinnately compound, up to 12 inches in length. Each leaf can have 7-13 (Chinese) or 13-19 (Japanese) leaflets, which are tapered at the tip and have wavy margins.
Flowers hang in showy, fragrant clusters which are 10-20 inches long. Blooms open sequentially from base to tip and can be lavender, pink, white, or violet blue.
Seeds are contained in velvety brown flattened bean-like pods, which may persist for some time on the vines.
Although the seeds are viable under favorable conditions, wisteria spreads primarily by vegetative growth. Stolons (above-ground stems) are produced which spread horizontally across the ground and develop new roots and shoots at the nodes.
Distribution: Wisteria can now be found throughout the eastern U.S. It is tolerant of a variety of soil, moisture, and shade conditions. Infestations are commonly found along forest edges, roadsides, ditches, riparian zones, disturbed sites, and in urban areas. Vines can climb trees, shrubs, and manmade structures.
Problem: Wisteria displaces native vegetation by girdling and killing it. The hard woody vines twine tightly around host tree trunks and branches and cut through the bark, eventually girdling the tree. 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. This process changes the forest structure as gaps are created in the canopy and an increased amount of sunlight reaches the forest floor. This may temporarily favor some native species but usually just stimulates the vigorous growth and spread of the numerous wisteria seedlings. Once established, wisteria can be very difficult to eradicate.
Control: A combination of manual, mechanical, and chemical control methods will yield the best results for controlling wisteria and minimizing impacts to native species. Vines climbing up trees or buildings should be cut as close to the root collar as possible and followed by the application of a concentrated systemic herbicide to the cut surfaces of the rooted living portions. Wisteria will continue to resprout until its root reserves are exhausted, so cutting should begin early in the growing season and continue every few weeks until the fall. Vines should be removed entirely from around trees or they will continue the girdling process even if cut at the base.
USE PESTICIDES WISELY: Always read the entire pesticide label carefully, follow all mixing and application instructions and wear all recommended personal protective gear and clothing. Contact your state department of agriculture for any additional pesticide use requirements, restrictions or recommendations.