Purple Loosestrife Removal Project
Purple Loosestrife
Common name: Purple loosestrife
Botanical name: Lythrum salicaria
Highly invasive: Purple Loosestrife (PL) is a very aggressive invasive plant native to Europe and Asia that appeared in North America during the 1800s. It has since spread to wild areas and degraded habitat for native plants and wildlife due to its fast growth rates, effective seed dispersal mechanisms and tolerance for a wide range of conditions. While native insects and diseases keep the plant under control in Europe and Asia, it has no natural predators here.
It is estimated that PL overtakes more than a million acres of wetlands in the United States each year. Left unchecked, PL forms massive, tall impenetrable stands that choke out native vegetation and take over ditches and waterways. No North American native animals will eat PL, and waterfowl will actually avoid wetlands where PL has a strong presence. PL will out-compete and crowd out native plants like cattails that provide food and home for native animals.
PL is “hardwired” to survive in Michigan. A mature plant can be seven feet tall and have 30-50 stems. It can produce over two and a half million seeds which can remain viable in the soil for over two years. PL seeds germinate several degrees cooler than native seeds thus giving it an earlier start in the spring. PL also sprouts from root tips left in the soil after digging the plant for disposal and from pieces of stems that fall in the stream after cutting or mowing.
Identification: PL can be identified by its large hot pink flower spikes that bloom from July through September. It is a tall plant ranging in height from 3’ to 7’ and has long green leaves with smooth edges usually in opposite pairs going up the stem. There are many stems on each mature plant. The stiff, 4-sided stems have ridges that you can feel and become woody at the base of mature plants. (Be careful not to confuse PL with Blue Vervain, a native plant with blue/purple flowers found in similar habitats that feeds several species of birds with its seeds and hosts the verbena moth and common buckeye butterfly.)
Methods of Control: PL removal on the Au Sable Mainstream has been a priority of ARPOA since 2009. Our original hope of eradication has realistically changed to control. There are three broad categories in which invasive plants are controlled:
1. Physical removal by cutting or digging is the best method for isolated plants and small infestation areas.
2. Chemical removal through application of herbicide is another effective method for controlling small infestation areas. However, it is complicated, risky and requires a MDEQ Aquatic Waters Permit. It is not recommended for large infestation areas.
3. Biological control through release of a natural predator from the plant’s native range (Europe and Asia) is recommended for medium and large infestation areas and does not require a permit.
ARPOA’s focus has been on physical removal and biological control, while chemical removal is too risky and complex.
Volunteer Events (Physical Removal): ARPOA has hosted over 20 volunteer events over the years to remove PL from the town of Grayling to McMasters Bridge, disposing hundreds of industrial bags full of roots and stems. Removal has gotten easier as we’ve refined our methods. After some experimenting, we are now cutting and bagging only the stems, flowers and seeds rather than digging up the root. Cutting will effectively starve the roots and eventually kill the plant within a few years. This allows us to cover more ground because it’s less work, faster and results in less bag waste. With consistent treatment year after year, the amount of waste lessens each time.
Thanks to dedicated ARPOA volunteers, the number of plants is less every year, making all the hard work very well worthwhile.
Beetles Release (Biological Control): Leaf-eating beetles which feed almost exclusively on PL were approved for use by the U.S. Department of Agriculture in 1992 after years of testing. The most common beetles used are the Galerucella pusilla and G. calmariensis. The beetles stress the plant, so they focus more energy on restoring themselves than on producing seed, stunting their growth, which allows native plants to recover.
During the mid-2010s, beetle releases were done by ARPOA and other companion organizations in areas with the densest plant populations on the Mainstream and South Branch. While there is some evidence the beetles are still present, “biocontrol” like any other method needs to be reapplied. In 2025, ARPOA carried out a Galerucella beetle release in a dense area along the Au Sable Mainstream with grant support from the Anglers of the Au Sable and the Mason-Griffith Founders Chapter of Trout Unlimited.
Keep an eye out for updates and removal events in our newsletters!