Issue No. 23, Article 11/October 7, 2005
There have been several questions about finding Japanese hops (Humulus japonicus) in Illinois this year. Japanese hops is listed as an invasive species for many states surrounding Illinois, and attempts should be made to control this weed.
Japanese hops, considered an annual, can be found in pastures, hayfields, roadsides, forest edges, and other noncrop areas. It reproduces by seeds, which are dispersed by wind and water. Japanese hops can form dense stands in floodplains and along streambanks and lakeshores, but it can also thrive in disturbed areas. It can be found in full sun or shade.
Japanese hops has climbing and trailing stems with long petioles and large, rough, five-lobed leaves. The stems have bracts where the petiole attaches to the stem. Stems also have small prickles that are turned downward. Leaves are usually 2 to 5 inches long. Japanese hops can easily be confused with wild cucumber (Echinocystis lobata) and native hops (Humulus lupulus). A very differentiating characteristic is the presence of tendrils on wild cucumber and their absence on Japanese hops. Native hops typically have three-lobed leaves (though upper leaves sometimes lack lobes), with petioles shorter than leaf length.
Options for control are limited to hand weeding (young seedlings) and spot applications of glyphosate before flowering.
For more information and pictures to help identify Japanese hops, visit the following Web sites:
--Dawn Nordby and Aaron Hager