Aggressive Japanese hop plant invading Southwestern Wisconsin

Japanese hop
Japanese hop can completely take over an area.

 

Aggressive Japanese hop plant invading Southwestern Wisconsin

By Ted Pennekamp

 

Japanese hop (Humulus japonicus) is a rogue aggressive plant that is invading crop fields, roadside ditches, and stream banks in Southwestern Wisconsin. Agricultural producers, landowners, hunters, and anglers are being asked to keep an eye out for this dangerous escapee and report any potential sightings to the authorities. This is one of Wisconsin’s most wanted invasive plants.

While Japanese hop is fast becoming “public enemy number one” in Southwestern Wisconsin, it is considered to be fairly isolated in Crawford County so far. The operative words being “so far,” however, because the insidious plant can spread rather quickly, according to Matt Krueger of the River Alliance of Wisconsin. 

“Each plant has thousands of seeds,” said Krueger, who noted that heavy rainfalls or flooding can cause the plants to fragment, which spreads the seeds to ever increasing areas. “It’s a fast-spreading vining plant and is very difficult to eradicate.” 

In Crawford County, Japanese hop is found mostly along Copper Creek, but Krueger said that monitoring efforts are underway to see how widespread the plant has become along the West Fork and the Main Fork of the Kickapoo River, where it was discovered last fall.

Krueger said that Japanese hop needs sunlight. Along with stream banks, it also is found in fields and ditches. Japanese hop was discovered growing in some large round hay bales recently. 

Authorities are trying to spread information about the plant to the public, but are also seeking information from the public as to the plant’s whereabouts. Farmers, hunters, anglers, and highway department workers (especially those who mow ditches) are encouraged to report any sightings.

Early detection is the key, said Krueger, who noted that Japanese hops can completely take over an area, squealching out other plants. When the hops die down in the fall, there are no other plants there to stop the resulting erosion.   

Japanese hop is a serious threat to crop production and water quality, as it can prevent the harvest of field crops, cause erosion that impairs the water quality of rivers and streams, and outcompete native plants that stabilize soil and create wildlife habitat.

This nuisance plant is a shallow-rooted vine that can climb over existing vegetation or structures to heights of 10 or more feet with the help of rough-textured stems covered with sharp spines. Its leaves typically have 5-7 lobes. Japanese hop reproduces by seed, and can be spread by wind and water. Recent infestations are thought to have been spread during flood events, as well as by maintenance vehicles and agricultural equipment.

Currently, Japanese hop is established in the Sanders Creek and Grant, Platte, and Castle Rock/Blue River watersheds in Grant County, Copper Creek watershed in Crawford County, the West Fork of the Kickapoo River watershed in Vernon County, and most recently in the Pine River watershed in Richland County. Any other suspected populations should be reported.

“We’re asking people to report Japanese hop, if they suspect they’ve seen it,” said Krueger. “Early detection is critical with this plant, as once it is established, it’s very difficult to eradicate. If we can catch infestations early, we stand a better chance of managing them.”

While physical and chemical controls can be effective at combating Japanese hop, landowners should not try to remove the plant on their own, or harvest and transport crops or hay off of sites infested with hop; the plant goes to seed in early fall, and attempted control efforts at this time could further worsen its spread.

For more information, or to report a suspected population of Japanese hop in Southwestern Wisconsin, contact Matt Krueger at the River Alliance of Wisconsin at 608-257-2424 x125 or Don Barrette at Southwest Badger RC&D at 608-348-7114.

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