Yellow flag iris
Latin Name: Iris pseudacorus
Origin: Europe, Asia, North Africa
Physical Description: It is a perennial herb from a thick rhizome. It has one to several smooth stems that grow up to 1.5m tall. It has dark green sword-shaped leaves with a raised mid-rib. Leaves are typically 90cm long and 3 cm wide. The showy flowers are yellow and have 3 sepals that curve backward and 3 petals pointing upward. It has a tuberous root that can be up to 20cm long, as well as pink, freely branching rhizomes that are 2-3cm in diameter.
Habitat: It prefers full sun to partial shade and areas that are moist/wet. It is often found in garden ponds, ditches, irrigation canals, marshes, streambanks, lakeshores, floodplains and shallow ponds.
Impacts: It can create dense stands that outcompete desirable riparian vegetation such as cattails, sedges and rushes. This impacts the available food and habitat for wildlife such as birds, fish and amphibians. It can also clog ditches and irrigation canals and reduce the water storage capacity in temperate wetlands, causing them to dry out. This plant is toxic to livestock if ingested and can cause skin irritations/blisters on people who come in contact with the plants resin.
Reproduction: It reproduces by seed and vegetatively by rhizomes. Plants take 3 years before reaching maturity and flowering. The flowers produced an average of 5.6 capsules/plant with an average of 120 seeds/capsule. The seeds have a hard seed coat with a gas space, allowing them to float in water. Research has show that seeds can stay viable in water for up to a year. Plants also have an aggressive root system that spreads rapidly. Root fragments can form new plants when they break off and drift downstream.
Mechanical: Pulling small infestations repeatedly over several years can eventually kill plants. Digging is effective but can fragment rhizomes which can produce new plants; ensure the entire root system is removed. Dead heading flowers prevents seed production but does not affect the plants. Cutting aboveground plants, then covering with durable PVC matting for up to 1 year is effective on land and in water. It is recommended that gloves are worn when handling this plant.
Chemical: No aquatic herbicide has been approved in Canada for treatment of Yellow Flag Iris in aquatic habitats. For plants that are present in dry upland areas, several herbicides with the following active ingredients can control Yellow flag iris: 2,-4-D, Glyphosate, and Imazapyr. For available products, contact your local agri-supply store. Prior to any herbicide application, read and follow the label instructions.
Biological: None available.
Invasive Species Council of BC’s Yellow Flag Iris Factsheet
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