Yellow Flag Iris is a highly invasive plant that forms dense stands in wetland areas, lakeshores, rivers, and streams. It outcompetes native species, disrupts water flow, and alters the natural structure of waterways. The plant can invade pastures, displace native vegetation, and is toxic to livestock. Its seeds are buoyant, easily dispersed by water, and can remain viable for over a year, making the plant difficult to control once established. Yellow Flag Iris negatively impacts the ecological health of water bodies, cultural values, and agricultural productivity.

Yellow Flag Iris is found across Otago, including Mosgiel, Lake Wānaka, Lake Whakatipu,  Lake Hayes, Tahakopa Estuary in Papatowai, and Oamaru. 

• Size: Yellow Flag Iris grows up to 1.5 meters tall.
• Appearance: It has broad, flat, sword-shaped leaves that form a fan shape from the base of the plant. The bright yellow flowers are up to 12 cm in diameter, with three large sepals and three small erect petals. The plant’s thick, fleshy rhizomes form dense mats and can float on the surface of water.
• Similar Species: It looks similar to Stinking Iris (Iris foetidissima), which has a foul smell when crushed, and Typha orientalis (Raupō), which has different flower heads and taller stems.
• Habitat: Yellow Flag Iris is commonly found along the shores of lakes, rivers, wetlands, and drainage systems. It thrives in both fresh and brackish water environments.

It is an offence to breed, knowingly communicate, exhibit, multiply, propagate, release, or sell, an unwanted organism (Biosecurity Act 1993).

Physical control

Dig out.

Plant parts requiring disposal: seeds and rhizomes.

Contact your local council for appropriate disposal locations.

Chemical control

No qualifications: Foliar spray with 100ml glyphosate per 10L of water.

Certified handler/experienced agrichemical user: Foliar spray with 100ml glyphosate per 10L of water and 20ml penetrant.

Caution: When using any herbicide or pesticide please read the label thoroughly to ensure that all instructions and safety requirements are followed.

Biological control

Biological control is currently not available for this species.