Purple loosestrife biocontrol — and you
Purple loosestrife (Lythrum salicaria) is a flowering plant that can reach 3’-7’ tall and is listed as a Restricted Invasive Species in Wisconsin because of its history of causing negative ecological impacts to wetlands and shorelines. Extensive populations of the plants that were found throughout the state by the latter half of the 1900s have been brought down to a manageable level in most areas thanks to tiny beetles and the people who rear and release them where needed.
- Check out the Purple loosestrife (Lythrum salicaria) fact sheet.
- Learn about Purple loosestrife identification.
- Learn about approved purple loosestrife biocontrol species.
Wisconsin DNR has been using four insects from Europe to control purple loosestrife since 1994. Careful research has shown that all four control species, referred to as biological agents, do not threaten native plants or cause other issues. For example, they do not overwinter in our homes. The process is classic biocontrol, and it is likely the best long-term control for purple loosestrife, reducing the need for other more costly and disruptive methods, such as herbicides or large-scale digging.
Two "Cella" beetle species (Galerucella calmariensis and G. pusilla) provide highly effective control by feeding on leaves and shoots. A root-boring weevil, Hylobius transversovittatus, can be effective but is difficult to monitor for success. A second weevil, Nanophyes marmoratus, feeds primarily on the flowers, reducing the amount of seed the plants can produce. It appears to have naturalized in some locations since being released in the early years of the three-decade biocontrol program.
The Galerucella sp. beetles are the easiest to intentionally rear and place where they are needed. They successfully decrease the vigor, size and seed output of purple loosestrife, allowing native plants to grow and compete. The purple loosestrife that remains can provide some benefits to pollinators when it is not eradicated. Keeping some of the plants on the landscape is also important to maintaining healthy populations of beetles. Successful biocontrol typically ranges from one to several years, depending on such factors as a site’s size and the purple loosestrife density. To improve landscape health and prevent the incursion of other Invasive species or a resurgence of purple loosestrife, many sites may need to have native plants re-established if there is no longer a good seed bank in place. Though elimination is rare, biocontrol offers effective and environmentally sound control of the plant without herbicides.
Wisconsin's Efforts to Control Purple Loosestrife
Since 1997 over a thousand people across the state have shared in the fun of rearing beetles and releasing them into local purple loosestrife populations in wetlands, lake and river shorelines, and ditches. Some folks have participated for over 20 years! There are several ways to help. The training videos below provide an overview of the program and describe the activities needed to be successful. Most projects are coordinated through a County’s Aquatic Invasive Species (AIS) Coordinator or other local program leaders. Check our Aquatic Invasive Species Contacts page to find your AIS Coordinator or reach out to the statewide Coordinator at DNRAISinfo@wisconsin.gov to learn how to participate where purple loosestrife biocontrol is still needed.
Important to remember: A permit is required because the process involves moving a WI-restricted invasive species from one location to another. The application can be found below in the Forms section.
Because Galerucella sp. beetles are now naturalized throughout Wisconsin, WDNR does not provide the parent beetles for rearing or release. This is not clearly stated in the current version of the program application. However, County AIS Coordinators and the Statewide Coordinator can assist in finding parent beetles in most cases. Collecting the beetles is what many people enjoy the most.“Collecting Beetles” is one of the training videos below.
- Purple Loosestrife Biocontrol Program Overview and Instructions guide.
- Check out the biocontrol program quick guide filled with pictures and the most important how-to information.
- This chart can help you determine what method or combination of methods make the most sense for your site: Integrated Pest Management for Purple Loosestrife, including Biocontrol.
- Video Training Series:
Help UW Madison Division of Extension Natural Resources Institute’s Aquatic Invasive Species Program evaluate our training videos and their use by taking this survey after you watch this and other videos in the series: Purple Loosestrife Training Follow Up Survey. You can repeat the survey for each of the videos in the survey or watch multiple videos and reply for all of them at once.
- To join the program, download and complete this application to send it to the address below.
- To report beetle release, download and complete the Purple loosestrife Beetle Release Form.
- To assess beetle activity at newly found and previously managed purple loosestrife patches, download and complete the Purple loosestrife Beetle Presence and Activity Report Form.
Educational materials for students:
- See Cella Chow! Here you’ll find lesson plans for grades 6-12 built around the science of biocontrol, specifically purple loosestrife. The lessons include a listing of the related Wisconsin Model Environmental Education and Science Standards.
Purple loosestrife is here to stay in Wisconsin, but you can encourage it to “play nice” with native plants by reuniting it locally with its natural predators. As biocontrol reduces purple loosestrife, you can experience even more satisfaction by helping to restore any native plants that may have been crowded out, further ensuring diverse, healthy wetlands!
For more information
Purple Loosestrife Biocontrol Coordinator
Purple Loosestrife Project
101 S. Webster St., WY/4
PO Box 7921
Madison, WI 53707-7921
To find learn if there is an upcoming training near you, contact the program coordinator or your county Aquatic Invasive Species Coordinator. The County Coordinators can be found at Wisconsin DNR AIS Contacts. Some counties may not have a coordinator, but there could be training in a county nearby.