My, What Yellow Flowers You Have: Yellow Flag Iris and Its Impacts

With warming spring temperatures comes the return of birdsong, rain showers, and beautiful blooms sprouting throughout the landscape. However, these blooms may include a particular yellow flowering plant to keep an eye out for. Yellow flag iris is an invasive semi-aquatic flowering perennial often seen growing along lake shores and rivers, as well as in wetlands and marshes. This plant was originally introduced from Europe and Asia as an ornamental plant used in gardens and landscaping, but it escaped to find itself in natural areas and is known to spread rapidly once established. Yellow flag iris quickly crowds out native vegetation. The plant can most easily be identified by its bright yellow flowers that bloom from April through June. The flowers grow on tall stems amongst the plant’s stiff, blade-shaped leaves that are dark green in color.

Blue flag iris is a native look-alike that may be mistaken for yellow flag iris. The most apparent differences between them are the colors of the flowers and the size of the plants. Blue flag iris flowers are blue-purple with a small yellow spot in the center of their sepals (petal-like appendages). Blue flag iris tends to be shorter than yellow flag iris, often growing 2-4 feet tall, whereas yellow flag iris tends to grow 3-5 feet tall. 

Yellow flag iris has two main vectors of spread: seeds and rhizomes. Yellow flag iris seed pods measure 2-4 inches long and can contain up to 100 seeds each. When mature, the seed pods open to release the seeds, which can float on water due to an air pocket between the seed and its outer casing. This method of spread can be especially detrimental to riverine systems, whose constant downstream water flow allows yellow flag iris’s floating seeds to spread quickly. Yellow flag iris can also spread vegetatively via their rhizomes (stems that grow horizontally underground) that can form large floating mats on the water’s surface. Because of these methods of spread, yellow flag iris is classified as invasive and is known to heavily outcompete native North American vegetation once it becomes established. The flowering plants are also poisonous to both humans and animals if ingested, making the plant unsuitable as a food source for wildlife. 

Manual removal and chemical treatment are the two main methods used to control yellow flag iris. Manual removal of yellow flag iris consists of digging out the plants using tools such as shovels. This method is best used on small populations of plants due to the labor intensity of the job. It is also important to note that wearing long sleeves and gloves is essential when manually removing yellow flag iris, as contact with the plant and its sap has been known to cause skin irritation. The second yellow flag iris management method is a chemical application using a water-safe herbicide. Before starting any management practice to control yellow flag iris, please check with your local DNR office to ensure you have the correct permitting. 

If you encounter a patch of yellow flag iris, the best action is to report the population. To do so, record details about the observation date, the approximate size and density of the population, and the location of the population, including latitude and longitude.  Be sure also to take detailed photos of the plants, including the flower heads and leaves. Then, you can send this information to your local WI Department of Natural Resources aquatic invasive species biologist or your local MN Department of Natural Resources aquatic invasive species specialist, whose contact information can be found on their respective websites. 

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