What to do about Gazanias

By Susanne Govella, Greater Wellington Regional Council

The pest plant biosecurity team in Wellington are quite excited about a control trial of Gazania spp. we will be carrying out on Wellington’s west coast during this coming season.

Gazania linearis and G. rigens are two species of garden plants commonly sold in New Zealand and Australia. The bright colours of their flower heads along with their ability to tolerate dry conditions and poor soils have made them popular among gardeners.

Gazanias are native to South Africa where they can be found from low altitude sandy soils to alpine meadows. Species of Gazania hybridise freely when possible, making identification of any Gazania challenging.

Outside their natural range, Gazanias are known to invade agricultural areas and roadsides and can rapidly out-compete native plants, leading to a decline in biodiversity. Their tolerance of dry conditions and poor soils means that Gazanias pose a significant risk to coastal plant communities in New Zealand. It is for this reason that Gazanias have been classified as a “red alert” species in several coastal management plants both in New Zealand and Australia.

The recommended control option for control of Gazanias has typically involved using the herbicide glyphosate, however the efficiency of this control option has now been questioned following a failed control operation in 2011 on Wellington’s south coast.

GWRC Biosecurity Department has been approached by Wellington City Council and Take Care community groups for advice regarding control of Gazanias in coastal ecosystems, following failed control operations and an increase of Gazania plants found in areas previously occupied by other pest plant species that had been successfully controlled.

Although herbicide trials for control of Gazania are currently being carried out by the Riverland Winegrape Growers Association in Loxton, Australia, the herbicides of choice, Amitrole and Diquat, are not recommended for use in fragile ecosystems such as coastal dunes in New Zealand. Therefore the Biosecurity Department plans to undertake control trials aimed at providing a reliable control method for use in fragile coastal ecosystems in the Wellington region.

The aim of this project is to carry-out a spray trial comparing the performance of four agrichemicals (Glyphosate, Grazon, Tordon XT and Versatill,) as a means of controlling Gazania spp.in coastal dune ecosystems. By the end of this trial we hope to be able to recommend either a proven control method for Gazanias in coastal dune ecosystems, or further research into developing reliable control methods for Gazanias.

The trial is an interdepartmental collaboration to assure it meets the scientific standards required by our new work procedures. It has been prepared by Nikki McArthur, Environmental science department, Darryl Kee and Susanne Govella Biosecurity pest plants at Greater Wellington Regional Council.

We are looking forward to report back our results after the completion of the trial in September 2014.