What does it look like?
Stinking iris is a clump‑forming perennial that grows up to 80 centimetres tall. It spreads from red‑brown underground stems (rhizomes). The leaves are dark green, leathery, and sword‑shaped, growing 60 to 100 centimetres long. When crushed, the leaves give off a strong, unpleasant smell.
Flowering stems grow upright to around 60-80 centimetres tall and produce dull yellow flowers in late spring and early summer. The flowers often have greenish‑brown markings and occasionally appear brownish‑purple. After flowering, the plant forms green, three‑sided seed capsules about five centimetres long. These split open to reveal many round, bright scarlet seeds.
Seeds are spread by birds, while rhizome fragments can be moved by water. Both seeds and rhizomes can also be spread by contaminated soil, machinery, and dumped vegetation. Stinking iris is commonly found along roadsides and in wasteland areas.
Why is it a problem?
Stinking iris spreads easily and forms dense, long‑lived clumps that smother the ground and stop native seedlings from establishing. It tolerates deep shade, hot and cold conditions, most soil types, and both dry and semi‑damp environments.
The seeds are poisonous and may harm birdlife. The plant is also unpalatable and toxic to livestock, and it can recover quickly after damage.
Control methods
Physical control
Weedmat: Cut tops, lay, and leave for three to four months.
Herbicide control
Foliar spray (spring to autumn) - Apply herbicide using a hand-held sprayer/knapsack. Apply a mix of Glyphosate (360 g/L active ingredient) herbicide at 15ml/L + metsulfuron herbicide (600g/kg active ingredient) at 0.3g/L + an organo silicone penetrant at 3ml/L and thoroughly wet all parts of plant. Note: Overspray will kill other (desirable) broadleaf plants and has residual activity in the soil which aids in killing below ground parts. Do not use over or near water bodies or wetlands and use only as directed on label.
Bared areas, both shady and open, can be reinfested from the seed bank, and rhizomes can resprout and are hard to kill. Exclude livestock at all times. Remove seeds if ripe and dispose of these. Replant with taller understorey species in forest sites, to minimise seedlings.
CAUTION: When using any herbicide or pesticide, PLEASE READ THE LABEL THOROUGHLY to ensure that all instructions and safety requirements are followed.
More information
Many Gladiolus and related species, and four other exotic Iris species, all of which have been found in the wild, are similar. Yellow flag iris (I. pseudacorus) is the only aquatic species with tall stems and yellow flowers.
Related links
