Yellow Flag Iris (Iris pseudacorus)

Factsheets

Description

Aquatic perennial growing up to 1.5 m tall.  Large, flat, strap-like green leaves emerge from thickened rhizomes in a distinctive fan shape.  Long stalks end in showy yellow flowers in parts of three. Can be confused with cattails (Typha spp.), but cattail stem bases are round, while iris stem bases are flattened.

Habitat

Yellow flag iris is native to Europe, western Asia, and north Africa.  On Galiano Island, it is found in creeks and along the margins of lakes and wetlands.

Impacts

Yellow flag iris can outcompete native wetland vegetation, reducing habitat for many native species.  It can clog waterways, alter hydrology, and make livestock sick if consumed.

Management

To limit population spread, cut, bag, and burn flower heads to prevent seeding.  To remove plants, carefully dig out and remove rhizomes, making sure to reduce fragmentation.  Several passes will be necessary to remove most rhizome fragments.  Seed germination and re-sprouding are to expected post-removal, and can be managed using a heavy rubber mat (such as a pond liner) as a “benthic barrier”.  Apply the mat for at least 70 days to ensure that remaining seedling and fragments are dead.  Removed plant material can be dried out in the sun on an impermeable surface, then discarded in the forest in a shady and dry area, or burned.

Alternatively, there is a *NEW* experimental method for yellow flag iris removal!  It’s called “deep water cutting“, and is effective under the following conditions:

  • The yellow flag iris population you are targeting is located in a permanently flooded area, like the margin of a wetland or pond where the water level is consistently high
  •  All above-water parts of the plant are cut beneath the water surface, so that roots and cut stems of the plant are fully submerged
  • Rhizomes and plants that are located on the bank are removed using the traditional method of digging and pulling (see above).  All rhizome connections between the plants on the bank and the submerged plants are severed completely either by fully removing bank iris and/or creating a trench between submerged iris and bank iris.
  • If submerged iris stems are cut below the water surface and remain there for several months, and all rhizome connections with plants that are located above water are severed, then submerged plants will die.

Our Experience

Iris is very difficult to remove once established.  Small populations can be managed by removing flower heads annually.  Removal requires repeated digging in the muck to remove rhizomes.  The use of a benthic barrier post-removal will reduce the need for future removal activities.  We will be experimenting with the new deep water cutting method.  Iris should be removed from native creeks and wetlands whenever possible, especially when it is upstream of bodies of water.

 

 

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