Auckland Council are looking for infestations of yellow flag iris to support research by Manaaki Whenua
Auckland Council is looking for infestations of the pest plant yellow flag iris to support research by Manaaki Whenua (Landcare Research).
Yellow flag (Iris pseudacorus) is increasingly becoming a problem in riparian and wetland areas in the Northland and Waikato regions. Large sections of the Waikato River are dominated by this plant. Plants have started to establish in Rodney and Waitakere. In response to this there is research underway to investigate whether there are insects or pathogens currently hosted by the plant in New Zealand. This contributes towards a larger project to potentially bring a biocontrol solution to this pest plant in New Zealand.
Although yellow flag is not as common in Auckland as it is in the neighbouring regions, having more infestation sites to study ensures more robust data for this research.
If you observe yellow flag iris on private land within the Auckland region, and the landowner is amenable to Environmental Services staff to checking the site, the infestation size and potentially facilitating a conversation between the landowner and manaaki whenua, then please get in touch with Rebecca Kemp (Rebecca.kemp@aucklandcouncil.govt.nz) or Callum Templeton (callum.templeton@aucklandcouncil.govt.nz) with the address and contact details of the landowner.
Yellow flag iris is native to Europe, Asia and North Africa. Introduced to New Zealand as an ornamental garden plant, it has since spread to sites throughout New Zealand. Yellow flag iris is a leafy wetland-terrestrial iris that grows up to 2m. It forms dense floating mats in shallow water and has thick creeping rhizomes (fleshy roots) with many rootlets. It grows in the margins of still, fresh or slightly salty water such as rivers, swamps, salt marshes and pond edges. It typically inhabits the margins of lakes, rivers or drains. Yellow flag tolerates frost, flooding, drought, nutrient-rich and nutrient-poor waters and many soil types. Much of the spread is by prolific seeding or by fragmentation of root rhizomes.
Yellow flag iris is native to Europe, Asia and North Africa. Introduced to New Zealand as an ornamental garden plant, it has since spread to sites throughout New Zealand. Yellow flag iris is a leafy wetland-terrestrial iris that grows up to 2m. It forms dense floating mats in shallow water and has thick creeping rhizomes (fleshy roots) with many rootlets. It grows in the margins of still, fresh or slightly salty water such as rivers, swamps, salt marshes and pond edges. It typically inhabits the margins of lakes, rivers or drains. Yellow flag tolerates frost, flooding, drought, nutrient-rich and nutrient-poor waters and many soil types. Much of the spread is by prolific seeding or by fragmentation of root rhizomes.
Current control methods include digging out, injecting individual rhizomes with herbicide or foliar spraying with herbicide. These methods are particularly labour intensive with the risk of impacting other plants and the environment in which they grow. Investigating biocontrol as a management tool for this plant offers the potential of wider scale gradual control that allows wetland and riparian areas to recover slowly.
Yellow flag iris is one of six national pest plants that are receiving funding from MPI to investigate biocontrol options.
More information about the biocontrol programme for yellow flag iris can be found here:
Weed Biocontrol Vol. 90Weedbusters – Using Citizen Science with yellow flag iris