Japanese Hops (Humulus japonicus) Control and Management Strategies in Large River Floodplains

Japanese hops (Humulus japonicus) is an invasive vine that establishes in open areas in riverine habitats and suppresses tree regeneration and native vegetation. This study evaluated the use of herbicides and tree plantings to control and manage Japanese hops on five Mississippi River islands over a four-year period. Herbicide treatments included a preemergent (sulfometuron methyl), a postemergent (glyphosate), and a combination of both. Tree plantings used containerized and bareroot American sycamore (Platanus occidentalis) and eastern cottonwood (Populus deltoides) trees. Japanese hops biomass was significantly lower in all herbicide treatments in 2012 and 2015, but the preemergent treatment was less effective than other treatments in 2012 and 2014. After two years, average survivorship of containerized trees was 20%–42%, whereas bareroot seedlings had near 100% mortality. Results indicate that postemergent treatments are effective for short-term control, but large floods reestablish Japanese hops in treated areas. Reforestation, if combined with herbicide treatments and active management, may be a promising approach in large river floodplains that experience frequent flooding, but low tree survivorship presents challenges to reforestation. Study Implications Japanese hops (Humulus japonicus) is an invasive vine that establishes in open riparian areas and suppresses tree regeneration and other native vegetation. We confirmed that glyphosate provides effective short-term control, but also found that large floods can quickly reestablish Japanese hops in treated areas. Bareroot seedling mortality was extremely high, but initial survival and growth rates of containerized trees were more promising. We conclude that tree plantings combined with active maintenance, including glyphosate application, may be a viable option for long-term control of Japanese hops in upper Mississippi River floodplains.