Several severe infestations of the invasive weed yellow flag iris were caught just in time thanks to responses from Whangarei District residents to a Department of Conservation postcard campaign on weeds.
DOC’s Northland Weed Surveillance Officer Liz Sherwood said “I visited most callers to identify the suspected plant and determine the distribution of the weed. On one property, I discovered yellow flag iris smothering a river bank. If the seeds had gotten into the stream, the weed would have spread very rapidly downstream.”
Ms Sherwood said DOC received approximately 35 calls from the public in response to the publicity postcards distributed to households in November and that she was very happy with the positive response.
Ms Sherwood said those people visited were keen to help the campaign by agreeing to remove the flower and seed heads now to help reduce its spread, while DOC would return to properties in autumn to spray or dig out the small patches. “In return for people’s effort we give them a native plant of their choice.”
“People have mostly been given cuttings of the iris from friends or family, and some of the cuttings have come from Auckland. Many of the gardeners have noticed the iris spreading through their garden.
“It is a concern to DOC that plants, such as yellow flag iris, that are banned from sale, propagation and distribution continue to be traded unknowingly by gardeners. There are a further 91 weed species on the National Plant Accord List which are banned from sale because they have proved to be invasive weeds. The list is produced by the Ministry of Agriculture and Forestry and is available at DOC and Northland Regional Council offices and at the Protect New Zealand website (www.protectnz.org.nz).”
Ms Sherwood said “We’ve sprayed the bulk of the yellow flag iris infestation at Waipu this month, although the changeable, wet and windy weather conditions have drawn out the programme. This first spray round is to knock back the bulk of the infestation and prevent the seeds from maturing then sprouting next spring.” She said the programme was a real team effort between DOC and the community.
Flower production is not impressive when compared with other irises, however, many viable seeds are produced from each flower. The large rhizomes (like tubers) allow the plant to bulk up quickly in damp environments where it can grow to a height of two metres and exclude other plants.
“It is not too late to report the whereabouts of yellow flag iris or any of the other ten ‘postcard weeds’ which DOC will remove free of charge. People can collect postcards from any DOC office.”
Ms Sherwood said “We will control these weeds because they are a huge threat to our natural areas, but they are uncommon enough that we can get on top of them if our community reports them.”