Yellow flag iris
Botanical Name
Iris pseudacorus
Family
Iridaceae (iris)
Also known as
Where is it originally from?
Europe, Asia, North Africa
What does it look like?
Robust aquatic perennial (<1-2 m) that grows in leafy clumps and forms dense rhizomes (<3 cm diameter). All parts are odourless when crushed. Stems are round, and several long sword-like leaves (1 m x 2-3 cm) emerge in fans from a reddish base. Pale-yellow to golden-orange flowers (up to 12 cm diameter, Oct-Dec) are followed by seed capsules (5 x 2 cm) containing many brown, flattened, 3-sided to disc-like seeds.
Are there any similar species?
Many Gladiolus and related species are similar, and there are four other exotic Iris species that appear in the wild. Iris pseudacorus is the only aquatic species that grows in clumps and has tall stems and yellow flowers.
Why is it weedy?
Rhizomes form dense floating mats, and it overtops native species that grow on margins of waterbodies Tolerant of saline, frost, flooding and drought, high-low fertility, many soil types, and damage. Poisonous, so usually not grazed by stock.
How does it spread?
Seeds and rhizome fragments are spread by water and contaminated machinery. 'Garden escape' plant that has spread from gardens and deliberate plantings into the environment.
What damage does it do?
Rhizome mats displace native plants, especially vulnerable species that live on the margins of waterbodies. Causes flooding and changes in the water levels in swamps. Poisonous seeds may have an impact on birdlife.
Which habitats is it likely to invade?
Swampy ground, fresh or brackish water margins, lakes, salt marsh, and wet sandy areas.
What can I do to get rid of it?
Begin control work at margins, working upstream to downstream where possible
1. Stem injection (all year round): 5ml glyphosate (undiluted) into each stem at base.
2. Spray (spring-autumn): glyphosate (100ml/10L + penetrant) or metsulfuron-methyl 600g/kg (0.5g/10L). Note: A resource consent is required to spray metsulfuron over water. Contact your nearest regional council for advice.
CAUTION: When using any herbicide or pesticide, PLEASE READ THE LABEL THOROUGHLY to ensure that all instructions and directions for the purchase, use and storage of the product, are followed and adhered to.
What can I do to stop it coming back?
Plant tall shading species adjacent to sites, and exclude livestock. Prevent seeding, and ensure regular follow-up of sites that have been controlled, as rhizomes resprout and seed bank can reinfest bared sites.
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