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 Japanese hops, a new weed species to be aware of in Wisconsin Minimize
Location: BlogsWisconsin Crop ManagerWeeds    
Posted by: WCM Staff 8/21/2008 4:15 PM
Last week we received two unknown weed samples for identification, one from a homeowner, the other from a field in southwest Wisconsin. The homeowner version was common hops, a native species or non-native variety of this species used for hop production for beer (Humulus lupulus). The other species in the agricultural field was Japanese hops (Humulus japonicus) a new non native invasive plant spreading in Wisconsin.

Japanese hops, a new weed species to be aware of in Wisconsin

Mark Renz, Extension Weed Scientist, University of Wisconsin-Madison

Last week we received two unknown weed samples for identification, one from a homeowner, the other from a field in southwest Wisconsin. Both samples turned out to be hops (Humulus spp.). The homeowner version was common hops, a native species or non-native variety of this species used for hop production for beer (Humulus lupulus). The other species in the agricultural field was Japanese hops (Humulus japonicus) a new non native invasive plant spreading in Wisconsin, see picture 1. While neither of the species would be desirable in an agricultural setting, one should be particularly aware of Japanese hops as it apparently can spread rapidly into natural, urban and managed areas, especially pastures and along fences, but also potentially in no-till fields. 
 

Picture 1: Infestation of Japanese hops in Lancaster Wisconsin.

 
What is Japanese hops? It is a non-native vine that can climb up to 8 feet in height. Its leaves are opposite (unlike wild cucumber,), 2 to 5 inches long, serrated on the edges and palmately divided into 5 or more lobes (upper leaves can be 3-5 lobed), see picture 2. This plant is diecous which means that male and female flowers are on separate plants, so while fruit which form in later summer are distinct, they will only appear on female plants.
 
How do I tell the difference between the two? The key features to distinguish between common hops and Japanese hops are the number of lobes on the leaves and the length of the petioles. Common hops tends to have 0-3 lobes on leaves (although they can have 5) with petioles that are smaller than the length of the leaf see pictures below. Japanese hops have leaves with 5 or more lobes and the petioles as long or longer than the length of leaves, see pictures below.
 
Common hops pictures: Leaf and fruit; note petioles are shorter than length of leaf, and fruit bracts do not have pointed, elongated tips.         

  

 

 
Japanese hops pictures: Leaf and fruit; note petioles are longer than length of leaf, and fruit bracts have pointed, elongated tips.
 

   

  

 
 
 
 Current spread of Japanese hops: While this species was first discovered in Wisconsin in 1918, it has recently been observed to be spreading throughout the Midwest (see current distribution map created by MIPN). Over the past two years five new infestations have been documented within Southern Wisconsin in natural, urban, and agricultural settings in addition to the populations identified at the herbarium. While it is unclear how populations have been spreading, one expert believes dissemination by water is a major pathway.

 

 
 
If I find some new infestations please report this sample to the Wisconsin Weed Watchers Program. Contact Brandon Panke the coordinator at Brendon Panke with the Wisconsin DNR as he is the coordinator for this program phone:(608) 267-7438 email: Brendon.Panke@wisconsin.gov. He will at a minimum require the location of the infestation, the gps coordinates, and date the infestation was initially found. This information will be used to identify locations, track the spread and allow for management when resources become available.
 
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