Photo source: University of Connecticut https://wiki.bugwood.org/Iris_pseudacorus
This invasive iris is also called “yellow flag” or “yellowtail” iris. It should not be confused with other yellow irises, including bearded and Siberian species.
This iris has invaded wetlands and shorelines across America, present in all but four states. It is native to Europe, Asia, and northern Africa and was imported to North America as an ornamental plant as early as the late-1700s. Yellow iris was discovered on the shore of White Bear Lake near the historic Fillebrown House in the summer of 2020 and treated later that summer.
Yellow iris expands quickly via rhizomes and forms dense mats of roots that crowd out native species, reduce the habitat available to native fish and waterfowl, and clog and narrow waterways. All parts of the plant are toxic to livestock and other animals.
If property owners see any of this growing on their lakeshore, they should arrange to have it removed as described below.
How to identify invasive yellow iris
It is a perennial aquatic herbaceous plant that grows one to three feet tall along shorelines or in shallow water. The leaves gradually taper (sword like shape) and are up to ¾ inch wide. They are green to blue-green in color. The center of the leave is sharply thickened. The leaves are stalkless and have parallel veins.
They bloom May-July. Two or three deep yellow flowers adorn one round stalk, shorter than the outer leaves. Three outer dropping sepals with brownish mottled markings surround the true flower. Oblong capsules contain numerous flattened seeds that look like thick coins. There is a short root system with stout rhizomes (roots).
How to control/remove invasive yellow iris
Wear gloves and cover your skin if working with the plant, as contact with the plant and its sap can cause skin irritation.
Small clumps can be dug out, though this is only effective if the rhizomes are entirely removed.
Mowed plants will regenerate from the rhizomes, so plants must be cut multiple times to exhaust their energy reserves. The sap may cause skin irritation, so gloves should be worn when handling cut or damaged stems.
Glyphosate herbicides approved for aquatic use (such as Rodeo, Roundup aquatic formula, and Aqua Star) can be effective, particularly if applied to recently cut foliage and stems. In Minnesota, eradication of such semiaquatic plants in public waters below the ordinary high water level (OHWL) requires a permit from the DNR. (For reference, the lake reached levels a few inches above the OHWL in 2019 and 2020.) If these irises are found growing outside public waters on private land, they may be controlled by property owners without a permit.
Minnesota DNR information on yellow iris: https://www.dnr.state.mn.us/invasives/terrestrialplants/herbaceous/yellowiris.html