Yellow Flag Iris Control on Lake Owen

Yellow iris is one of just two invasive plants present in Lake Owen. The other aquatic species is aquatic forget-me-not, another shoreline plant.   Although it is a showy, flowering plant, we are working to remove it from our shorelines. A USFS fact sheet reports “it can form dense colonies and impenetrable thickets in fresh or brackish water displacing native species and altering habitat for animals. All parts of the plant are poisonous.”    For more information on about this invasive species, go to:

Our lake manager crew identified and marked yellow iris in 19 locations along Lake Owen shores in 2019. We received permission to chemically treat these plants to remove them at all but one of the locations shown in the map. This included permission to remove the plants from US Forest Service land. Although it is a good idea to remove seed pods to prevent yellow flag iris spread, manual removal efforts in other lakes have proven ineffective in controlling yellow iris.

The Contractor Dale Dressel, from Northern Aquatic Services, completed the Lake Owen Association-sponsored yellow iris treatment on September 4, 2019. He treated a total of 18 sites. Dale also collected 8 pounds of yellow iris seed pods.

The Lake Owen Association is working to control invasive yellow iris. If you believe you have yellow iris on your property and have not been contacted by an LOA representative previously, please contact our Lake Manager, Cheryl Clemens (harmonyenv@amerytel.net or 715-268-9992). Crews will be out in June to identify yellow iris for potential control in 2020.Yellow iris monitoring and control is eligible for 75% grant funding through our Wisconsin Department of Natural Resources Lake Protection Grant.

Description of the plant:

Leaves & stems : Broad, sword-shaped leaves grow upright, tall, and stiff. They are green with a slight blue-grey tint and are very difficult to distinguish from other ornamental or native iris species. Flowers are produced on a stem that can grow 3-4 feet tall amongst leaves that are usually as tall or taller.

Flowers: Showy and variable in color from almost white to a vibrant dark yellow. Flowers are between 3-4 inches wide and bloom from April to June. Three upright petals are less showy than the larger three downward pointing sepals, which may have brown to purple colored streaks.

Fruits & seeds: Seeds are produced in fruits that are 6-angled capsules, 2-4 inches long. Each fruit may have over 100 seeds that start pale before turning dark brown. Each seed has a hard outer casing with a small air space underneath, which allows the seeds to float.

Roots: Thick, fleshy pink-colored rhizomes (underground stems) spread extensively in good conditions, forming thick mats that can float on the surface of water.

Similar species: When not flowering, yellow flag iris could be easily confused with the native blue flag iris (Iris versicolor) as well as other ornamental iris that are not invasive. Blue flag iris is usually smaller and does not tend to form as dense clumps or floating mats. When not flowering or showing fruiting bodies, yellow flag iris may be confused with other wetland plants such as cattails (Typha spp.) or sweet flag (Acorus spp.) species.

 

Control Methods

Mechanical:

Small populations may be successfully removed using physical methods. Care should be taken if hand-pulling plants as some people show skin sensitivity to plant sap and tissues. All parts of the plant should be dug out – particularly rhizomes and disposed of in landfill or by burning.
Cutting the seed heads may help decrease the plant spreading.

Chemical:

Aquatic formulas of herbicides may be used to control yellow flag iris, however, permits may be needed. Foliar spray, cut stem/leaf and application and hand swiping of herbicide have all shown effectiveness.

The Wisconsin DNR approved the Lake Owen Association application for the treatment of invasive Yellow Iris at Lake Owen in 2019.  The DNR letter and accompanying permit is as follows:

Lake Owen 2019 APM Permit