Purple loosestrife in Lake Leelanau, Michigan.

Combating Purple Loosestrife in Lake Leelanau

Driving along the lake, you might notice a purple flower in bloom along Lake Leelanau’s shoreline and wetland areas. While beautiful, purple loosestrife is a dangerous invasive species threatening our wetlands. We invite you to read the following to learn more about the impacts of purple loosestrife in Lake Leelanau and how you can help protect the watershed.

"Wanted Purple Loosestrife in Lake Leelanau" graphic, Lake Leelanau Lake Association

What is purple loosestrife?

Originating in Europe and Asia, purple loosestrife (PL) is a perennial herb that has invaded Michigan’s wetlands. The plant can grow 4-10 feet tall, with leaves that start out with a lance-shape, but become very variable in shape as it grows. 

Purple loosestrife's woody roots can have 30-50 square, woody stems and opposite leaves. This invasive plant is in bloom from July through October, and the flowers are a vivid purple making it easy to spot from a distance.

Image collage of purple loosestrife

What problems does purple loosestrife cause? 

Purple loosestrife forms monocultures that replace native plants, reducing critical food resources for birds, butterflies, and other wild creatures. Not only do purple loosestrife seeds germinate very rapidly, it grows faster than almost any wetland plant. This makes it very easy for it to out-compete native species.

When purple loosestrife enters an area, its stiff stems can collect debris such as silt (sedimentation). This can dry up a shallow water habitat and make it into a terrestrial site, destroying the habitat for native aquatic animals. Furthermore, the stems of purple loosestrife are unwelcoming to waterfowl, so waterfowl do not frequent these areas.

How is purple loosestrife managed?

Once established, purple loosestrife is difficult to control and likely will only partially disappear if in a large patch. The best thing to do is monitor natural areas and work to remove purple loosestrife as soon as it is spotted. 

There are three approaches to control; digging it up, obligate beetles, and herbicides. The plant is difficult to dig up, and any remaining roots can start a new one, so the removal must be complete to be effective. Literature suggests that Galerucella beetles can be a moderately effective biological control. They are considered a loosestrife obligate insect meaning they only eat loosestrife. The beetle damages the plant and prevents it from spreading further, creating a monoculture of loosestrife. Unfortunately, the beetles can not eliminate the plant entirely but can help lessen its spread.

While many people object to herbicide use, and for good reason, invasive species experts often turn to herbicides when the infestation is extensive, or digging is not an option. Unlike herbicide application to plants submerged in the water (like Eurasian watermilfoil), herbicide for purple loosestrife is applied directly to the plant. This direct application minimizes its impact but still kills the plant. Although seeds in the soil will likely germinate for some time, requiring repeated treatment.

We must tackle this invasive species and keep Lake Leelanau’s natural shoreline environment healthy.

What is LLLA doing about purple loosestrife?

LLLA has contracted an environmental consulting firm, One Less Consulting LLC, to complete a terrestrial invasive species (TIS) survey of Lake Leelanau and the Leland River. One Less Consulting recently completed a survey looking for purple loosestrife. This was one of the 2023 goals set by the Lake Association to continue to broaden our work to protect the lake. 

The survey indicated small patches of purple loosestrife around the shoreline and in the river. However, there is a substantial infestation of the invasive plant along the northern shores of South Lake Leelanau and in the Narrows.

Combating purple loosestrife in Lake Leelanau

The Lake Association plans to begin tackling the infestation this year and continue for several years or maybe longer to get it under control. Precise plans for controlling purple loosestrife are currently being decided upon and will be publicized upon approval by LLLA’s board.

Homeowners can help this plight by digging up plants on their property and removing flowers before seed heads develop.  

Another idea is for your neighbors to get together and contract a certified herbicide applicator to spray the infestation. The Leelanau Conservation District has listed local certified herbicide contractors here.

If your property is located in the area the Lake Association has targeted for treatment this year, One Less Consulting LLC will contact property owners to sign a permission form allowing the consultant to treat the infestation of purple loosestrife. 

We greatly appreciate your support in eradicating this highly invasive species. For more information on purple loosestrife, visit the Northwest Michigan Invasive Species Network website.

If you have any questions regarding purple loosestrife in Lake Leelanau, please send an email to [email protected]. We are happy to help!

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