Yellow Flag Iris - Iris pseudacorus

Description: Yellow flag-iris is native to Europe and the Mediterranean region, including North Africa and Asia minor. It was introduced into eastern North America in 1911 and into British Columbia in 1931 (Department of Natural Resources and Parks Water and Land Resources, 2009).

Yellow-flag iris is a perennial herb with large showy yellow flowers. They have 3 large downward facing sepals and 3 smaller erect petals. The yellow flowers often have purple/brown veins at the base of the petals. Flowering stalks can produce one to several flowers. The leaves are found at the base of the plant and clasp the stem. A mature plant can range from 1-1.5m tall. At the base of each plant is the root system that forms a dense mat. This mat can be 1m in diameter and extend to 30cm deep (Simon, 2008).

Type: Perennial

Habitat and Impacts: The preferred habitats of Yellow-flag iris include freshwater wetlands, fens, ponds, lake shores, rivers, stream banks, wet pastures and ditches. These plants tend to grow more proficiently in shallow waters however they can form extensive mats in deep water. This iris species tends to displace natural aquatic and riparian vegetation and reduces critical fish and wildlife habitat. This plant can also cause gastroenteritis in cattle and skin irritation in humans (Simon, 2009).

Method of Spread: Yellow-flag iris spreads by seed and roots via water. Because it can reproduce by its roots, an entire infestation can be connected by the same root system. Also, if a piece of root is broken off it is possible for that fragment to form a new plant. Root fragments that dry out can re-establish if they become wet again. (Simon, 2008).

Location: Yellow-flag iris has been classified as a new invader in the Cariboo Chilcotin Coast area. It is thought to occur in the Central Cariboo in the city of Williams Lake near Scout Island.

Management Options:

Mechanical: Small infestations of Yellow-flag iris can be managed by hand pulling young plants that are not yet established. Larger plants can be dug out, ensuring as much of the root mass is removed as possible. Mowing or cutting prior seed set may also be effective by reducing seed production. This is a long term method of control that must be done persistently over several years.

Chemical: Chemical control is difficult as most herbicides cannot be sprayed near water. Chemical application can be achieved by carefully wiping/wicking herbicide on the emerged portion of the plant or by stem injection. Glyphosate has proven to control Yellow-flag iris (Department of Natural Resources and Parks Water and Land Resources, 2009).

Biological: There is no biological control agent available in British Columbia for this plant.

CCCIPC Priority and Treatment Strategy: Priority 1 (new invader) in all sub-regions. The current management objective for Yellow-flag iris in the Cariboo Chilcotin Coast region is elimination via chemical and mechanical treatment.

Treatment Options:

Local Level – frequently hand pulling and/or digging small infestations.
Landscape Level – Mechanical and Chemical application where possible.

Yellow Flag Iris plant

Yellow Flag Iris flower


Invasive species profile taken from the Cariboo Chilcotin Coast Invasive Plant Committee Invasive Plant Regional Strategic Plan

Page last modified: March 15, 2017 09:36:29 PDT