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

Terrestrial Invasive Plants in the Lake Leelanau Watershed

Much of Lake Leelanau Lake Association’s (LLLA) recent focus has been on aquatic invasive plants, most notably Eurasian watermilfoil. In this post written by LLLA Stewardship Committee member Stuart Winston, we want to turn our attention to terrestrial invasive plants that have also found their way to our watershed. We invite you to learn more about terrestrial invasive plants in the Lake Leelanau watershed, so you can join our efforts to prevent the spread!

When are non-native plants considered invasive?

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 our lake’s water quality.

Invasive plants in the Lake Leelanau watershed

The following focuses on three prominent players in the Lake Leelanau watershed: Yellow flag iris, purple loosestrife, and phragmites.

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

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.

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 the beneficial cattail. 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.

Purple loosestrife (Lythrum salicaria), invasive plant in the Lake Leelanau watershed
Purple loosestrife (Lythrum salicaria)

Purple Loosestrife (Lythrum salicaria)

Like yellow flag iris, purple loosestrife produces a pretty bloom, described by most as rose-purple. Another Eurasian native, it got to the US in 1833 (maybe because it was carried as a medicinal) and was already in northern Michigan by 1844. 

Purple loosestrife thrives in wet soils, marshes, and ponds; along streams and riverbeds; and on lakesides. It can grow as high as 10 to 12 feet, and a single plant might have dozens of stems arising from its roots. Flowering starts in mid-June.

What is the problem? Purple loosestrife is very competitive and rapidly displaces native species—it can inhibit nesting by waterfowl. Like the yellow flag iris, it can trap sediment, block water flow, and reduce open waterways. 

How do we get rid of it? Pulling by hand or digging is the preferred method for smaller infestations—but ensure you remove the flowers before seeds form. Chemical control is recommended for larger infestations where pulling by hand is impractical. Fun fact: Researchers have successfully controlled the spread using four species of a small natural predator—beetles!

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

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 ssp. australis) from the native, beneficial reed (Phragmites australis ssp. 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? 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.

We hope that you join us in watching out for signs of these terrestrial invasive plants and participate in whatever way you can in their mitigation. Together, we can stop the spread of invasive plants and protect the Lake Leelanau watershed.

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