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Noxious Plant Alert by Doug Karman

Updated: Aug 4, 2023

Let’s be proactive on Long Lake and manage this plant before the problem is so severe that the County Noxious Weed Board must get involved.

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The clear sap produced by this plant is poisonous to humans and animals when ingested and can cause painful rashes when skin is exposed to its juices.

Yellow Flag Iris grows in water, its stiff leaves extending upwards like cattails. It grows in wetlands, along lakes, rivers, and streams, but it can thrive in drier habitats, too. It has showy, bright yellow flowers. It often remains green year-round. in our mild winter climate, leading. many homeowners around Long Lake to transplant the iris into their yards. Residents also like this plant because it breaks up their shoreline and provides a buffer at the edge of the lake. However: This Plant Must Go!


IMPACTS: The plant’s dense rhizomes (tuber type roots) crowd out native vegetation, trap sediment, and inhibit stream flow, degrading fish, and wildlife habitat. They spread around the lake, down the outlet and up into yards and across lawns. CAUTION!! The clear sap produced by this plant is poisonous to humans and animals when ingested and can cause painful rashes when skin is exposed to its juices. We’ve had two severe reactions in Thurston County that led to emergency room visits: a rash over most of a homeowner’s body after using a weed whacker on it, and a lesion covering the cheek of another person who dug out the plant. These each took more than two weeks to begin healing. We’ve also had a case of a dog with lesions and sores here on Long Lake. Yellow flag iris spreads by seeds and by rhizomes. After blooming, 3” seed pods grow in clusters at the base of the flower. The seeds are buoyant and easily move to different areas of the lake. The orange rhizomes form dense mats and can also float, then break apart to establish new colonies.


CONTROL: Since the sap is poisonous and may cause a severe skin rash, waterproof hand protection and long sleeves should always be worn when handling this iris.

1. The first and most important step to take in keeping this plant from spreading further in Long Lake and downstream into Woodland Creek is to remove the seed pods. Clip the pods, put them in plastic bags, and into the trash, never in any compost. Small clumps of yellow flag iris may be dug out and put in the trash.

2. Remove the plant from your waterfront or yard. This plant can be removed by digging it out, including the roots. Roundup and similar herbicides that you can buy in a hardware store are not approved for aquatic uses; they contain surfactants that are toxic to aquatic organisms. If your iris grows along the shore or in the water, you’ll need to hire a licensed aquatic applicator to treat your plants.

3. It will be important to make sure all eradication measures have completely removed the yellow flag’s orange rhizomes before planting something else. That will only complicate matters if the iris re-sprouts while control work is still underway.




CONSEQUENCES: While removing the iris is still optional on Long Lake, it is a noxious plant, and the County Noxious Weed Board has required its removal on Lake Lawrence. If this happens on Long Lake, it will mean a fine if you fail to do so, and noxious weed staff will remove it at your expense. Let’s be proactive on Long Lake and manage this plant before the problem is so severe that the County Noxious Weed Board must get involved.

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