What is Yellow Flag Iris?
Yellow flag iris is an aquatic invasive plant found in Lincoln County that readily impairs wetlands, rivers, and streams. These aquatic habitats are critical to numerous sensitive fish and wildlife species, which makes control of yellow flag iris particularly challenging. Yellow flag iris is classified as a State Listed B noxious weed and is considered an Early Detection Rapid Response (EDRR) species, and should be reported by emailing Lincoln Soil and Water Conservation District (LSWCD) and the Oregon Invasives Hotline. In Lincoln County, its relatively sparse presence makes it a priority species for early detection and control so as to prevent more serious infestations. The ISCP is currently inventorying infestations of yellow flag iris within rivers, streams, and wetlands throughout Lincoln County. If you know of an infestation, email our Program Manager or call (541) 265-2631.
Physical Description
Growing up to 6 feet tall, yellow flag iris is the largest iris species found in Lincoln County, towering over any other varietals and natives. It is a perennial native to Europe that was introduced as a garden plant, and a water treatment species (accumulates heavy metals) in the United States. It spreads by dislodged fragments of its underground rhizome (see photo below) or by its corky seeds, which can float. During the late spring months, its yellow flowers are a good identifier. A good place to see this species in Lincoln County is at Brian Booth State Park, formerly known as Ona Beach State Park.
Why is Yellow Flag Iris a Problem?
Yellow flag iris is a very large and aggressive species that grows quite successfully in standing water such as wetlands and streams. Its dense growth habit rapidly out-competes and excludes the native vegetation that wetland wildlife are dependent upon for food and shelter, such as sedges and rushes, while the iris itself does not provide meaningful food or shelter. In small and swift-moving streams, yellow flag iris can clog waterways and alter flow patterns, leading to flooding.
Controlling Yellow Flag Iris
Yellow flag iris is very difficult to control due to its expansive root system, which deeply penetrates the soil substrate. Removing all portions of the roots and rhizomes is necessary for manual control. But without caution, digging can lead to the spread of rhizome fragments. Herbicide application to control yellow flag iris should be conducted by a licensed applicator due to treatment occurring in and around water. If you have a yellow flag iris infestation on your property, you can help prevent its spread through the local watershed by clipping, bagging, and properly disposing of any flowers before they go to seed. Do this with caution, as the sap from this plant has the potential to cause temporary skin irritation.