Japanese hop

Humulus japonicus

Invader Images

    • Japanese hop leaves have 3-9 lobes, with a toothed margin.
      Japanese hop leaves have 3-9 lobes, with a toothed margin.
    • Japanese hop infestation
      Japanese hop infestation
    • Japanese hop stems have small prickles.
      Japanese hop stems have small prickles.
    • Japanese hop cluster
      Japanese hop cluster

Common Look-alikes

    • Humulus lupulus variety lupuloides syn. H. lupulus ssp americanus (other H. lupulus varieties are native/non-native)- https://plants.usda.gov/core/profile?symbol=HULUL, https://gobotany.newenglandwild.org/species/humulus/lupulus/
      Humulus lupulus variety lupuloides syn. H. lupulus ssp americanus (other H. lupulus varieties are native/non-native)- https://plants.usda.gov/core/profile?symbol=HULUL, https://gobotany.newenglandwild.org/species/humulus/lupulus/

Identification

Appearance

Humulus japonicus is an annual, climbing or trailing vine that is native to eastern Asia. This vine has 5-lobed leaves (generally), downward pointing prickles on the stem and bracts at the base of the petioles.

Foliage

Leaves are opposite, rough, 2-5 in. (5-13 cm) long, 5-9 lobed with toothed margins. Most leaves will have five lobes, but the upper leaves may only have three.

Flowers

Flowers originate in the leaf axils and are green with five petals. Male and female flowers occur on separate plants (dioecious). Female flowers occur in cone-shaped clusters that hang down and the male flowers occur in upright flower stems.

Fruit

Fruit is a yellow-brown ovoid achene. The small seeds are distributed by wind and water.

Ecological Threat

These vines can grow to 35 ft. (10.7 m) in one growing season, allowing them to infest large areas crowding and out competing native vegetation. Humulus japonicus was introduced into North America in the mid-to-late 1800s as an ornamental.

Biology

ECOLOGICAL THREAT

Japanese hops can form dense patches that outcompete and smother native vegetation.

ORIGIN

This vine is native to China, Japan, Korea and Taiwan. It was brought to the U.S. in the mid-to-late 1800s as an ornamental and as a medicinal plant. This is not the type of hops used for beer making.

HABITAT

Meadows, fields, disturbed areas

LIFE CYCLE

Japanese hops is an annual, climbing or trailing vine that can grow up to 35 feet in length in one growing season. Female flowers appear in mid summer as cone-shaped clusters that hang down (called hops), while male flowers are upright and stemlike.

Management Options

This is considered a watch list species.

MECHANICAL MANAGEMENT

Manual and Mechanical The plants may be pulled in late spring and early summer, before they flower and set seed, typically prior to August. Be sure to wear gloves as protection from the hooked hairs that may cause blistering of the skin. When pulling, remove as much of the roots as possible, as the plant may resprout. Bag and discard all plant material. Repeated cutting or mowing close to the ground may also be used, however its effectiveness is limited as vines quickly re-grow from cut stems.

CHEMICAL MANAGEMENT

Chemical A pre-emergent herbicide, which kills weed seeds as they germinate, may be used on Japanese hops. This will reduce the impact to other vegetation. Combining a pre-emergent with later application of a glyphosate herbicide may provide longer-lasting control. The herbicide should be applied to the leaves, ideally when the rootstock is accumulating energy reserves (July through September).

 

**Be careful not to damage or kill nearby native plants when conducting management work. And when using herbicides, always follow the instructions on the label.**