BIOSECURITY Biosecurity series – pest plant factsheet FACTSHEET Yellow flag iris 23 Iris pseudacorus Plant type: Perennial semi-aquatic Plant type Other common names: Yellow iris Aquatic Yellow flag iris is native to Europe, Asia and north Africa. Introduced to New Zealand as an ornamental garden Fern plant, it was first recorded growing wild in the Hutt Valley in 1938. It is present at isolated sites throughout New Grass Zealand, but is currently banned from sale, propagation and distribution. Ground cover Why it is a pest plant Yellow flag iris forms dense stands that can displace Shrub native species and restrict access for recreational activities. Some infestations are the result of deliberate Tree plantings, but most spread is by prolific seeding or by fragmentation of root rhizomes (horizontal stems that Vine send out roots and shoots). It can also invade and displace Identifying features low-lying pasture, and is toxic to livestock. The largest Yellow flag iris is a leafy wetland-terrestrial Toxic established stands grow on both sides of the Waikato iris that grows up to 2 m. Forms dense floating River, particularly downstream of Ngaruawahia, but the mats in shallow water. It has thick creeping species is also establishing elsewhere. It typically inhabits rhizomes with many rootlets. Plants die back in the margins of lakes, rivers or drains. winter. Disposal Related species Flowers Compost Stinking iris (Iris foetidissima) is not aquatic. It is a smaller It produces large yellow flowers from plant with dull yellow-green flowers and its crushed leaves September to December. Flowers are up to 120 Herbicide have a foul smell. mm in diameter and are typically iris-like in form. Bury deeply Habitat Yellow flag iris. Margins of still, fresh or slightly salty water Report it such as rivers, swamps, salt marshes, pond edges. Tolerates frost, flooding, drought, high or low water fertility and many soil types. Fruit Seed capsules contain many smooth, flattened seeds which float on water. Leaves Broad flat sword shaped leaves, in fans from reddish base. Leaves are 20–30 mm wide, with a distinct mid-rib. www.waikatoregion.govt.nz Yellow flag iris seedlings. Photo: Trevor James Important contacts Biosecurity pest plant contractors in the Waikato region – 0800 BIOSECURITY (0800 246 732). Yellow flag iris infestation. For information phone the Waikato Regional Responsiblity for control Council’s freephone 0800 800 401 or check In all parts of the Waikato region, land occupiers are responsible for the total out www.waikatoregion.govt.nz/pests. control of yellow flag iris on their property. If the land is less than 20 m from a waterway, control may be undertaken subject to an approved Waikato Regional For more information on Council programme. pest plants, check out www.weedbusters.org.nz. Yellow flag iris is banned from sale, propagation, distribution and commercial display. More information Regional Pest Management Strategy (RPMS). How to control yellow flag Herbicide control What makes a pest a pest? – A guide to the ‘Weed wipe’ or spray with glyphosate (such as roundup) or metsulfuron (such as Waikato Regional Pest Management Strategy escort) plus a penetrant (such as Pulse). (free). Smaller infestations may be controlled by ‘injecting’ herbicide into the rhizome. Plant Me Instead – Plants to Use in Place of Common Pest Plants (free). Follow-up control work is likely to be required. The New Zealand Pest Plant Manual (National Note: If applying herbicide over water, a resource consent may be required. Please Pest Plant Accord Identification Guide) – check with the Waikato Regional Council before proceeding. $10.00 incl. GST. When using herbicides: Poisonous Plants and Fungi in New Zealand – • read the instructions on the manufacturer’s label closely A Guide for Parents, Schools and Child Minders • always wear protective clothing ($15.00 incl. GST). • always minimise the risk to desirable plants • contact the supplier for further advice. Waikato Regional Council, 401 Grey Street, PO Box 4010, Hamilton East 3247. For more information call the Waikato Regional Council’s freephone 0800 800 401 or visit www.waikatoregion.govt.nz. Waikato Regional Council biosecurity factsheet series no. 23. Updated September 2011 (S2775-0811).
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