Help Wanted Battle Purple Loosestrife

Purple Loostrife Update:

Purple loosestrife is in full bloom around many Michigan lakes and roadside wetlands. The Main Lakes Chain of Lakes has an established, yet sporadic population of Purple loosestrife. The plant has been targeted for control as it is highly invasive, displacing native shoreline plants and degrading critical shoreline habitat. Because this particular plant is currently a lower control priority than plants like Eurasian milfoil and Phragmites, we are relying on volunteers to help us contain and remove it. We need your help!

Refer to the photos below for assistance in identifying this plant. Look for purple it pinkish flowers in clusters on shoreline plants with angular to square stems. The plants don’t flower until mid to late July so often they go unnoticed until the mid-summer bloom occurs. If you roll the stems in your fingers, you will notice the angular or square nature of the stem. Very few native shoreline plants have angular stems.

Purple Loosestrife is a prolific seed producer and incredibly hardy. Mowing the plant will not kill it and in most areas that the plant is mowed, it continues to out compete native vegetation and spread. Spraying adult flowering plants will also increase the spread of the plant. Roundup-like systemic herbicides will kill adult Purple loosestrife plants but all native plants contacted are also killed. The seeds are not affected by systemic herbicides and will germinate and repopulate the treated area. Seeds are often viable for multiple years.

The best way to remove PL is to carefully pull or dig it up and dump it in a trash bag. The tap roots often run fairly deep and unless they are completely removed, the plant will return. The picture below shows the authors attempt at removing a plant by pulling. The shallow roots pulled out but the tap root remained. It is likely a new plant will sprout from this root next spring. Another option is to cut all the flowers off the plant and dump them in a trash bag. The remaining green leafy (seedless) vegetation can then be sprayed with Roundup. Thank you for your willingness to help and please don’t hesitate to contact me with any questions.