Editor's note: This is the first in a series of articles by Kristina Swerhun, co-ordinator of the Sea to Sky Invasive Species Council, about invasive plants that are common in the Sea to Sky Corridor.
Invasive yellow flag iris (iris pseudacorus) is an eye-catching plant - the only yellow iris that occurs in Squamish wetland environments - and poses a significant threat to surrounding ecosystems. Currently only small populations have established in Squamish, making for the ideal scenario for a successful eradication.
Native to Europe and the Mediterranean region, yellow flag iris has showy yellow flowers from May to July, with sword-shaped leaves. Its leaves are usually longer in the centre and fan out in a single plane toward the edges of the plant. The leaves are dark green to blue/green, and may remain green during mild winters. Stout rhizomes, one to four centimetres thick, form dense mats up to 30 cm deep. When not flowering, it could be confused with cattail (typha latifolia), which is round at the base and taller than yellow flag iris.
Yellow flag iris is a problem for many reasons. It colonizes quickly and spreads in dense stands and rhizome mats, displacing native plants and decreasing biodiversity. It also reduces habitat and resources available for wildlife, since very few native wildlife species can use this plant for food or habitat. Habitat and the width of water courses is also altered since the plant can compact soils, trapping sediments and restricting water flow. Plants also clog small streams and irrigation systems, and seeds can block pipes.
Yellow flag iris is difficult to eradicate once established, since it is dispersed by broken rhizomes and by seeds. A small sliver of rhizome can grow into a new plant and seed pods are buoyant and can remain afloat for up to seven months, allowing it to spread over long distances down watercourses.
How should the plant be effectively removed? First, take caution: all plant parts are poisonous, so wear gloves if you're planning to handle this plant. It can cause vomiting and diarrhoea and will sicken livestock if ingested. Contact with the resins in the leaves and rhizomes can cause skin irritation.
The first priority is to deplete future seed sources by removing all flowers and seed heads. Where possible, dig up and remove manually as much of the above- and below-ground plant material. If it is not possible to remove rhizome material, clip or break the plant as close to its base as possible. In both cases, removal sites should be monitored regularly over a few years and new growth should be removed or cut back. Never compost invasive plants, since buds and flowers can still form viable seeds after being dug up. All invasive material should be treated like garbage and end up in the Squamish landfill.
Help your community protect local resources by managing invasive plants. There are hundreds of native aquatic plants that are critically important to parts of a lake or river ecosystem, and alternatives are available to replace this attractive invasive.
For more information on identifying and getting rid of yellow flag iris, please contact your local municipality or the Sea to Sky Invasive Species Council at [email protected] or (604) 935-7665. For more information, visit www.ssisc.info
