Extension Educator for Fillmore and Houston Counties
When most people hear the word hops, they think of the common hop used for brewing beer. But over the past five to ten years a related species, Japanese Hops, has been invading the local waterways of southeastern Minnesota.
Japanese hops is native to eastern Asia and was originally brought to North America as an ornamental. It is an aggressively growing, annual vine that can both climb and trail across the ground. When climbing, the vines can put enough weight onto trees and shrubs that they break or fall over. On the ground they can develop such a thick mat of vegetation that no other plant species can grow in those areas.
For those interested in identifying the plant, the leaves of Japanese hops are two to six inches long and have five to seven lobes with toothed edges. The plants have hooked climbing hairs that can cause dermatitis and blistering if they come into contact with skin. There are distinct male and female plants that usually flower in mid to late summer. Japanese hops is often mistakenly identified as bur cucumber or wild cucumber but neither of these species have the hooked climbing hairs.
The species was first identified in Minnesota along the Mississippi in 2011 and was added to Minnesota’s Noxious Weed List in 2012. An extensive infestation along the Root River from Preston to Hokah was mapped in 2014. With only a few infestations in Minnesota, the Minnesota Department of Agriculture and the Minnesota Department of Natural Resources have made it a goal to eradicate these infestations quickly before the plant has a chance to spread. To this effect the Root River infestation was first treated in 2015. The Department of Natural Resources intends to complete another round of treatment this year in the same area.
Japanese hops is on the Eradicate List of noxious weeds in Minnesota, and so attempts must be made to kill the above and below ground parts of this plant. Japanese hops reproduces by seed which can be dispersed by wind, water, vehicles and equipment. Do not plant Japanese hops seeds and make every attempt possible to prevent the movement of these seeds. This is especially important for those who use the Root River for recreation purposes. Repeated hand pulling can control small infestations but repeated cutting and/or foliar applications of systemic herbicides are typically required to control larger patches of this weed species.
Much of the information for this article came from the Minnesota Department of Agriculture website and through direct correspondence with Emilie Justen, Noxious Weed Eradication Coordinator for the Minnesota Department of Agriculture. The Minnesota Department of Agriculture website on Japanese hops contains more information on this noxious weed as well as a map of the currently known areas of infestation in Minnesota. If you identify Japanese hops on lands outside of those mapped on the Minnesota Department of Agriculture website, please contact Emilie Justen by phone at (651) 201-6360 or by email at Emilie.justen@state.mn.us.
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