What’s That Weed?

Introduced species:  Kudzu (Pueraria lobata)

Characteristics:  Kudzu is one of the best-known examples of invasive plants in the United States. It is a fast-growing vine in the pea family, with stems reaching 20 meters (66 feet–yep, you read that right) or more in length.  The leaves are compound, with three leaflets; the terminal leaflet usually has three rounded lobes, while the others have two.  The whole leaf is 10-15 cm (4-6 inches) long and roughly as wide.  Reddish-purple flowers are borne from July through September in dense, showy spikes 10-20 cm (4-8 inches) long.  These give way to hairy, dark-brown, pea-like seed pods 6-8 cm (2.5-3.5 inches) long (though the plant rarely sets seed in colder climates).

Spread:  Kudzu’s rapid vegetative growth is the stuff of legend, particularly in the southeastern United States, where it occasionally overruns vehicles, houses, and small children.  It can spread by seed, and vegetatively both by rooting at stem nodes and by rhizomes.  Native to Japan and East Asia, it was introduced in the US in the late 1800s for erosion control, and quickly escaped control.  It is currently spreading at a rate of 150,000 acres per year, with some 7 million acres infested in the US.  So far, there have been three infestations located in Oregon (one in Clackamas County and two in Multnomah County); all three have been treated. This is one of 15 weeds on a “mandatory eradication” list in the City of Portland; they will provide free assistance to citizens in identifying nuisance plants and methods to remove them.  Contact the Bureau of Environmental Services Early Detection Rapid Response team at 503-823-2989 if you think you have any of these species growing on your property.

Control:  Manual control can be achieved by removing the root crown and any rooting runners; the roots themselves do not resprout.  The root crown is a fibrous knob of tissue that sits on top of the root (rhizome). Crowns form from vine nodes that root to the ground, and range from pea-size to basketball-size.  Cutting the crown away from the roots will kill the plant.  Several herbicides are also effective.

Native Replacements:  An excellent native vine species is hairy honeysuckle (Lonicera hispidula).  Growing best in full sun, it produces showy pink flowers, and will grow very well as a replacement for kudzu.

Well, kudzu’s flowers are kinda pretty…
…but it’s maybe a little aggressive.
Pretty flowers AND I can keep my car? Sold! (Hairy honeysuckle)
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