Pest Plants


Traditionally the Council has played a strong role in assisting and advising landowners with primary production pest plants, such as gorse and ragwort. More recently landowners are taking a greater interest in protecting and enhancing native biodiversity on their own land and that in the public domain. Council staff are increasingly being called upon to provide advice on the control of environmental plant pests such as moth plant (Araujia sericifera) and tradescantia (Tradescantia fluminensis)

Generally good progress has been made to meet performance targets but there are some areas of concern:

  • Data inconsistencies or gaps in the monitoring records.
  • Data deficiencies means that it is difficult to assess the success/failure of strategies and status of emerging pest plants

As part of the Biosecurity department's quality system work is being carried out to improve the gaps in data identified above.

New Zealand Pest Plant Accord (NZPPA)

As part of a national collaboration between the Nursery Association and local and central Government, biosecurity staff annually visit nurseries and other outlets which sell plants to look for plants banned from sale and distribution under the Biosecurity Act 1993. No unwanted organisms were found in any establishments this year.

Council staff also monitor for Notifiable Organisms under the Biosecurity Act. There are five pest plant species that fit into this category; water hyacinth (Eichhornia crassipes), cape tulip (Homeria collina), water lettuce (Pistia stratiotes), salvinia (Salvinia molesta) and Johnson grass (Sorghum halepense). Two infestations of salvina (Salvina molesta) have been found in the Whangarei area.

Biological Control Monitoring


Strains of the English gorse thrip (Sericothrips staphylinus), that were released in the mid nineties in the Uretiti and Poretu areas, did not survive in Northland or thrive anywhere else in New Zealand. So four populations of the more robust Portuguese strain were released in the Far North in January 2006. Thrips are most likely to affect the growth and survival of gorse seedlings and regrowth, because they prefer the new young shoot growth.

Monitoring of the other gorse agents for example, soft shoot moth (Agonopterix ulicetella) and pod moth (Cydia ulicetana), found insects at low infestation levels at release sites. Re-release of the soft shoot moth may be considered as populations are doing very well in the South Island. The hard shoot moth (Pempelia grandipennis) has been deemed a failure and no further work to try to establish populations in Northland will be attempted.


Monitoring of the ragwort flea beetle (Longitarsus jacobaae) found that reasonable populations exist throughout the region, therefore no collecting and relocating was required in 2005-2006.

Bridle creeper

A survey of Asparagus asparagoides (smilax or bridle creeper) by Landcare Research staff has found a pathogen (rust) attacking the plant, causing considerable damage. It is thought the rust may have blown over from Australia. Council Biosecurity officers have been monitoring for instances of the rust in the Northland region, with one infestation confirmed in Whatitiri. Landcare Research scientists are currently investigating the best methodology to move it around and Council Biosecurity Officers will then be charged with that responsibility.

Pest Plant Operational Monitoring

  • 63 African feathergrass sites were inspected with density at all sites substantially reduced to three to ten plants. No plants were found at 12 sites and therefore these sites no longer require control work but remain under surveillance.
  • Inspection and control of 200 lantana sites was undertaken in the Whangarei District between October 2005 and June 2006. Dargaville & Te Kopuru urban areas were also targeted and a large number of plants controlled in private gardens.
  • 74 scattered infestations of Manchurian ricegrass that are outside of the main infestation area of the Northern Wairoa River are annually inspected and controlled. Two new sites have been found recently on the Kaipara harbour at Hukatere and one in Whangarei. Manchurain ricegrass is notoriously difficult to control and thus only five of the 74 sites recorded severe dieback in 2005-2006.
  • 39 properties were inspected for nassella tussock and 33 plants were found on only six properties and controlled. 24 properties, which have had nassella controlled, have remained clear of the pest plant for the last three years.
  • Monitoring reveals that 70 hectares of spartina exists in the Mid and Far North with 45 hectares now included in the control program. Monitoring of 32 controlled sites in the Kaipara Harbour was undertaken, 12 sites were clear with no regrowth found. The remaining infestations underwent further control works. Aerial monitoring of spartina in the Hokianga Harbour found 40 new locations totaling approximately 30 hectares; one third of this is now included in a control programme.
  • No new infestations of the 12 surveillance plant species (‘the dirty dozen'), listed below, were found during the monitoring in 2005-06. The Rhammus alaternus, evergreen buckthorn, site has been progressively reduced in size over the last 10 years. The remaining area, about one hectare, was controlled during 2005-2006.

The Dirty Dozen

  1. eelgrass (Vallisneria gigantea)
  2. senegal tea (Gymnocoronis spilanthoides)
  3. hydrilla (Hydrilla verticillata)
  4. nardoo (Marsilea mutica)
  5. water poppy (Hydrocleys nymphoides)
  6. needlegrass (Stipa tenuissima)
  7. skeleton weed (Chondrilla juncea)
  8. evergreen buckthorn (Rhamnus alaternus)
  9. old man's beard (Clematis vitalba)
  10. houttuynia (Houttuynia cordata)
  11. entire marshwort (Nymphoides geminata)
  12. fringed water lily (Nymphoides peltata)

Pest Plant Compliance Monitoring

  • 123 sites of Bathurst bur and 120 sites of nodding thistle were all monitored at least once during the year to ensure that property owners achieved complete control of all plants. 24 sites of Californian thistle were identified during 2005-2006.
  • All operating quarries were inspected and most sites were found to be to complying with the rules of the Regional Pest Management Strategies. Several quarries were requested to do work and are working towards compliance. No formal instructions to clear, under the Biosecurity act 1993, were issued during 2005-2006.