July’s Weed of the Month may sound like a beer lovers’ delight, but it’s far from it. Japanese hops (Humulus japonicus) is a noxious weed that’s been reported along river corridors in the southeastern Minnesota counties of Houston and Fillmore (view map). Native to eastern Asian, Japanese Hops thrives in rich soils, riparian areas, and sunlight. The weed displaces native plant species, growing over vegetation, and prevents native plant regeneration. Though related to common hops (H. lupulus), Japanese hops cannot be used in beer production because it lacks the oily resins that give hops their unique flavor and aroma.
Japanese hops has many characteristics to distinguish it from other vines. It is an annual, herbaceous vine which reproduces by seed that can survive Minnesota winters. The green leaves have five or more lobes with toothed margins. Both the leaves and stems have hooked hairs that can catch on clothing and may cause blisters after contact. The vines grow quickly, twining in a counterclockwise direction up other plants, fences, or structures, and sprawl along the ground to form dense mats. Mats ten feet tall can form within a single summer, according to the Wisconsin Department of Natural Resources. There are separate male and female plants, and they flower in mid-summer followed by fruit.
Japanese hops has several look-alikes. As mentioned, it can be confused with common hops; however, common hops has 0-3 lobes on the leaves and is perennial. Bur cucumber (Sicyos angulatus) and wild cucumber (Echinocystis lobata) may also be mistaken for Japanese hops, but can be distinguished because the cucumber varieties do not have hooked, downward-pointing hairs on the leaves and stems and they have tendrils on the stem.
Japanese hops is a target weed on Minnesota’s Noxious Weed Eradicate List, which means all above and below-ground plant parts must be destroyed as required by law. Recommended management practices include the following:
To report infestations of Japanese hops or any other noxious weeds on the eradicate list, please notify MDA by email at firstname.lastname@example.org, or phone 1-888-545-6684 (toll-free).
See the Japanese Hops webpage for more detailed information.