Reed Mannagrass and Water Dropwort

Help us to locate these invaders in your neighborhood

SEWISC is currently partnering with the Wisconsin Department of Natural Resources (WDNR) and Stantec Consulting Services Inc (Stantec) on a three-year early detection and response project to control water dropwort (Oenanthe javonica) and reed mannagrass (Glyceria maxima) along the Bark River in Waukesha County, Wisconsin. Early detection is extremely important because invasive species can quickly establish, becoming difficult and costly to eradicate.

Reed mannagrass is a semi-aquatic, perennial grass that can grow up to 8 feet tall. This species invades wetlands, including swamps, lakes, ponds, slow-moving rivers, creeks, ditches, and wet pastures, where it forms monospecific stands that are capable of crowding out native vegetation. It degrades wetland habitats because it is not suitable for nesting and is a poor food source for wildlife. This species is classified as Restricted in Waukesha County according to Wisconsin’s NR 40 Rule.

Water dropwort is an aggressive forb that grows in shallow aquatic habitats and wet or moist sites.  This species spreads rapidly, developing into a ground cover plant that quickly moves into wetlands and choke streams if released in or adjacent to natural areas. This species is classified as Prohibited in Waukesha County according to the NR 40 Rule.

In early 2017, SEWISC began outreach to residents with known populations along the Bark River to acquire permission for treatments and educate them on the need for long-term control. With landowner permissions in place, Stantec was able to initiate control efforts in August and September 2017 using targeted herbicide applications. Follow-up herbicide treatments will be performed in 2018 and 2019. Revegetation efforts will include establishment of native vegetation after sufficient control of the invasive species. Establishing native plants will stabilize the surface soils in areas where vegetative cover was reduced as a result of treatments, provide competition against future invasion by invasive species and provide habitat for native wildlife.

Help us identify additional populations of water dropwort and reed mannagrass in southeastern Wisconsin to expedite early detection and rapid response efforts by reporting any populations of these invading plant species immediately to the WDNR.