Yellow flag iris

Yellow flag iris thrives in wet areas, such as ditches, irrigation canals, marshes, streambanks, lakeshores, floodplains and shallow ponds. It requires high water content in the soil but does not need to be submerged. It can grow in water up to 25 cm deep, and will thrive in full sun to partial shade. Yellow flag iris is currently widely distributed in British Columbia’s southern interior, and is particularly abundant in the Okanagan Valley and Central Kootenays.  

• Yellow flag iris creates dense stands that outcompete native wetland species such as cattails, sedges and rushes, reducing habitat for birds, fish and amphibians.   
• Dense patches traps sediments and slow water flow, causing waterbodies to dry out.  
• Can be toxic to livestock when ingested.  
• Contact with the resins can cause skin irritation and blisters in people.  

The most effective way to ensure that your lands do not become infested with yellow flag iris is by prevention. Here are some recommendations to prevent invasion:  

• Do not plant yellow flag iris; suitable replacement species include native cattail, a semi-aquatic perennial plant, or Siberian iris.  
• Maintain natural habitats in a healthy, vigorous condition to ensure a competitive plant community. 
• Regularly patrol your property for yellow flag iris plants and immediately control or remove infestations before seed set.  
• Take special care when controlling yellow flag iris near streams or ditch lines, to prevent the movement of plant parts and seeds downstream. 
• If you live alongside an infested shoreline, cooperate with neighbours and encourage them to prevent yellow flag iris spread. 
• Immediately re-vegetate or replant disturbed riparian areas or wetlands to prevent invasion.  
• Do not move contaminated soils to a new area.  

• Careful digging of the entire plant can be effective for small outbreaks. Manual removal must be repeated annually. Be sure to wear long sleeves and gloves as the sap can cause skin irritation. All plant parts, including the roots, must be removed and disposed of at a landfill. 
• Cutting aboveground plants, then covering with pond liner or heavy PVC matting can work on land or in the water if there are few obstacles. This technique is expensive and the cover needs to stay in place 4 – 12 months.  
• Monitoring of control techniques is required for several years, and re-planting of native species may be required. 
• No aquatic herbicides for yellow flag iris have been approved for use in Canada.  
• Backyard composting is not recommended as the temperature will not become hot enough to destroy the seeds and roots.  
• There are currently no biocontrol agents (natural insect enemies) available for use in BC.