Yellow flag iris, phragmites, and purple loosestrife invasive plants in the Lake Leelanau watershed.

Non-native plants are considered invasive when they can colonize and become a threat to the diversity of native species—therefore, a threat to the natural function of ecosystems. When that ecosystem is in our lake’s watershed, the effects “downstream” can adversely affect water quality. The following focuses on three prominent terrestrial invasive species in the Lake Leelanau watershed: purple loosestrife, yellow flag iris, and phragmites.

Purple Loosestrife (Lythrum salicaria)

Purple loosestrife in Lake Leelanau, Michigan.

Driving along the lake, you might notice a purple flower in bloom along the shoreline and wetland areas. While beautiful, purple loosestrife is a dangerous invasive species threatening our wetlands. It got to the US in 1833 (maybe because it was carried as a medicinal) and was already in northern Michigan by 1844.

Identification

Purple loosestrife is easy to identify when it blooms from July-October. Its flowers are a vivid purple, arranged at the top of the plant in pairs or whorls. It can grow 4-10 feet tall, and its flowers can produce over two million seeds the size of ground pepper, making it highly capable of spreading. It also spreads via its woody taproot, rhizomes, and vegetative growth. Purple loosestrife thrives in wet soils, marshes, and ponds; along streams and riverbeds; and on lakesides.

What is the problem?

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 do we get rid of it?

Once established, purple loosestrife is difficult to control. The best approach is to monitor natural areas and work to remove purple loosestrife as soon as it is spotted.

There are three approaches to control:

  1. Dig it up. The plant can be difficult to dig up, and any remaining roots can start a new plant, so the removal must be complete to be effective.
  2. Obligate beetles. 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 or creating a monoculture of loosestrife. The beetles can not eliminate the plant entirely but can help lessen its spread.
  3. Herbicides. 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 unintentional impact. However, seeds in the soil will continue to germinate for some time, requiring repeated treatment.

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

What is LLLA doing about purple loosestrife?

LLLA contracted an environmental consulting firm, One Less Consulting LLC, to complete a terrestrial invasive species (TIS) survey of Lake Leelanau and the Leland River. 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 there is a substantial infestation of the invasive plant along the northern shores of South Lake Leelanau and in the Narrows in addition to small patches of purple loosestrife around the shoreline and the Leland River.

 

We are employing the Integrated Pest Management (IPM) approach recommended by State Natural Resources agencies and invasive species experts.  The IPM approach is used to manage pest damage by the most economical means and with the least possible hazard to people, property, and the environment.  For homeowners with purple loosestrife infestations, our suggested course of action is as follows:

  1. If a property has less than 10 purple loosestrife plants, we are asking the property owner to dig them up and dispose of them in their garbage.
  2. If a property has more than 10 purple loosestrife plants and digging is problematic, we are asking that the property owner consider using an herbicide to kill the plant ONLY if there is no standing water immediately surrounding the plant.  Only Certified Pesticide Applicators may spray herbicide in areas with standing water surrounding the plant.
  3. If a property has more than 10 purple loosestrife plants and there is standing water immediately surrounding the infestation, we request that you consider contacting a Commercial Business Pesticide Applicator to perform the work.
  4. If you live in an area where many properties have purple loosestrife plants, LLLA will be working with property owners to deploy the Galerucella beetle that exclusively feeds on purple loosestrife plants. This technique is used extensively in the Midwest to keep the plant in check.  A permit from EGLE to release the beetles is not required, as they have been found to be safe and effective at controlling the plant.
2023 Purple Loosestrife shoreline survey results
2023 Purple Loosestrife shoreline survey results

Galerucella Beetles

In 1994, the State of Michigan joined five other states and Ontario in a USDA-guided biocontrol program and released thousands of non-native leaf-eating Galerucella beetles into native wetlands.  The results were a significant decrease in purple loosestrife and a significant increase in native plant populations without unintended consequences. There is consensus amongst the scientific community that the benefit of controlling purple loosestrife outweighs the minor risk of damaging some non-target plants*.

Yellow Flag Iris (Iris pseudacorus)

Yellow flag iris near water.
Yellow flag iris (Iris pseudacorus)

The problem with the perennial yellow flag iris is that it is pretty and a horticultural favorite. According to the US Geological Survey, this Eurasian-native plant arrived in North America in 1871, got to Michigan in 1937, and was first spotted in northern Michigan in 1954. It probably “escaped” from gardens early and now is a thriving invasive.

Yellow flag iris blooms from May to early July and prefers wet areas along shores, roads, and mud. It is easy to identify because it is the only primarily yellow iris (the blue flag iris that blooms later is native). This plant grows between 1 ½ to 3 feet tall, spreading by its abundant seed production and vigorous rhizome growth.

Yellow flag iris rhizomes courtesy of the South African National Biodiversity Institute.
Iris rhizomes courtesy of the South African National Biodiversity Institute (SANBI)

What is the problem? The yellow flag iris regularly crowds out native species like beneficial cattails, sedges, and rushes,
reducing habitat for birds, fish, and amphibian species. Its dense rhizome mats can block water flow and trap sediment. And it is poisonous to animals.

How do we get rid of it? The best non-herbicide method is to dig up the entire plant and dispose of it in the garbage (not compost). Effectively removing the rhizome network enhances success. Cutting off the blossoms (before capsules form with seeds) can reduce spread but is less effective. We recommend wearing gloves and long sleeves as the sap causes skin irritation.

Yellow Flag Iris resources

Phragmites or Common Reed (Phragmites australis)

Phragmites or common reed (Phragmites australis ssp. australis) along a river bank.
Phragmites or common reed (Phragmites australis ssp. australis)

Four species of these large perennial reed grasses are found in wetlands worldwide. The non-native species probably arrived in New England in the early 19th century and became the dominant invasive reed in Michigan by the middle of the 20th century.

The following can help you differentiate invasive reed (Phragmites australis) from the native, beneficial reed (Phragmites americanus):

  • The australis leaves are lighter than the americanus;
  • Australis stems are smoother and have a red color;
  • Australis can grow to be between 6 and 13 feet in height, and;
  • The flowers of the australis are feathery.

What is the problem? These reeds provide positive ecosystem services in other parts of the world where they are native—it is made into musical instruments and eaten in some areas. However, the stands of the invasive version can block access to shorelines, making the local habitats less suitable for wildlife and easily outcompeting native species. It is not uncommon that these reeds also interfere with human recreation on the water.

How do we get rid of it? Unfortunately, this is not a simple task. Once an invasive reed establishes itself, removal by hand is likely useless. If you find a grove of this invasive plant, please contact the Midwest Invasive Species Information Network (MISIN)—do not attempt to remove it yourself. The mitigation process becomes more complex with large infestations and can call for herbicides, mechanical removal, and even prescribed burning.

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