Humulus japonicus Siebold & Zucc.

Japanese Hops

Threat Level	Category
Emerging	Vine

Description

Height

Japanese hops is an annual vine, climbing or trailing from 1.5 to 8 feet long or more. In areas with milder winters, it may act as a perennial.

Leaves

Foliage is rough-hairy with a heart-shaped base and petioles longer than the blades. There are bracts at the base of the petiole. Leaves are 2 to 5 inches long and have 5-9 lobes (typically 5) with toothed margins. Leaves on the upper section of the stem may have fewer lobes.

Stems

Branched, rough stems have downward pointing prickles.

Flowers

Greenish male and female flowers occur on separate plants (dioecious) in summer and are inconspicuous. Pistillate flowers form cone-shaped clusters that hang down. Staminate flower clusters are upright.

Fruits

Yellow to brown achenes are small and distributed by wind and water.

Images

Image: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
More images of Humulus japonicus

Life History

Japanese hops, in the Hemp Family (Cannabaceae), reproduces by seed and in Tennessee is spread primarily along streams. The species can tolerate lower light levels but prefers more sun. In preferred habitat, the species can grow up to 35 feet in one growing season to produce dense, monotypic stands outcompeting nearly all other species.

Habitat

In Tennessee, Japanese hops primarily invades riparian areas, but can be found in other disturbed habitats. The species is spread by water and can rapidly colonize stream banks, forming extensive patches. While the species has been collected sporadically throughout the state, extensive infestations have been reported along the Powell River and Red River in north east and north central Tennessee, respectively.

Origin and Distribution

Japanese hops is a native of east Asia and was introduced as an ornamental in the 1800s. It now occurs over much of the eastern U.S. and small portions of adjacent Canada.

Management Recommendations

Mechanical

Hand pulling and cutting can be effective for managing small infestations. Mechanical removal should occur early in the year before the species has developed an extensive root system and before individuals set seed. Mechanical control would need to be conducted for multiple years due to the presence of a viable seed bank.

Chemical

Foliar application of an herbicide like glyphosate can provide control of the species. In milder areas where the plant shows perennial tendencies, apply the herbicide July to September for more effective root kill.

Sources

Flora of North America. Humulus.
Gleason, H.A and A. Cronquist. 1991. Manual of Vascular Plants of the Northeastern United States and Adjacent Canada. New York Botanical Garden.
Invasive Plant Atlas of the United States.
New England Wildflower Society Go Botany.
BugwoodWiki.