Plant Pest Control

With over 300 pest plant species in our region, controlling these pests is a huge job. Our region’s biodiversity is threatened by pest plants which can choke lakes, degrade wetlands, collapse forest canopies, smother regeneration in natural areas, and invade alpine and tussockland. 

Horizons employs biosecurity staff across the region. They have primary responsibility for inspection, enforcement, advisory and monitoring activities. They're responsible for organising contractors to carry out control work on zero-density plants and enforcement work.

Under the Biosecurity Act Horizons produces and implements a Regional Pest Management Plan. The Plan is to prevent new incursions of pest plants and manage the impacts of those pest plants already established.

View the Regional Pest Management Plan 2017-37.


Biological Control

Biological control or biocontrol has resulted in substantial pest plant management gains through the use of one living organism to control another. It has proven particularly useful for controlling widespread weeds that are well established, that are heavy seeders, or have large seed banks. Once the agents are well established there is generally no need to make further releases as the population disperses and becomes self-sustaining. However, it can take many years (decades even) for the population to build up to a point where it impacts substantially on the host plant.

It is worth noting that successful biocontrol does not usually eradicate its host. Success may mean a reduction of infestation size, vigour, or abundance into the foreseeable future. It should be viewed as a tool that complements other weed management options. Biocontrol may reduce population levels to a point where control using physical or chemical methods is minimised, or even unnecessary.

The biocontrol programme exists to carry-out releases of new and existing agents against entrenched pests, raise awareness of the programme and support research into new agents. For more information check out the Landcare Research website.

Yellow Bristle Grass

Yellow bristle grass is an annual summer grass which is invading pastures from roadside infestations, via stock movement and in infested hay, balage and silage. Like many weeds, yellow bristle grass will readily colonise bare ground areas that have recently been sprayed.

Yellow bristle grass is likely to have been present in the Horizons Region for decades. It is not a declared pest in this region but in response to increasing concern, Horizons is promoting awareness and encouraging management practices to minimise its spread.

Wilding Conifer Project

The Wilding Conifer Management Group includes; Horizons, the Department of Conservation, Forest companies, Bay of Plenty, Waikato and Hawkes Bay Regional Councils, Tasman, Marlborough and Queenstown Lakes District Councils, Environment Canterbury, Environment Southland, Land Information NZ, High Country Federated Farmers, Landcorp Farming, Royal Forest and Bird Society, and Scion.

The present idea to form a Wilding Conifer Management Group and to seek funds from the SFF originated in late 2005. The project aims to promote and improve the understanding of wilding conifer spread ecology and basic control strategies. It has three core objectives:

  1. Improving the assessment of Wilding Conifer spread risk, and the prioritisation of control operations. The major output will be via GIS maps.
  2. Determining the most appropriate and cost-effective techniques for removing wildings and killing standing conifers - a major output will be a handbook of the most user-friendly, safe and cost-effective operational control methods, plus how to audit and monitor them efficiently.
  3. Determining vegetation successions after wilding invasion and control, so that they can be manipulated towards the most desired vegetation cover (often native species). 

Preventing Freshwater Weed Invasions

Our region has been forged by rivers, and along with our lakes they are sources of food and enjoyment for many of us. By checking for pest weeds and pest animals, and cleaning your gear or drying it thoroughly, you will be protecting our waterways. Unfortunately we have several freshwater pests already causing problems in our region. By following the simple steps of 'Check, Clean, Dry' we can stop the spread of these pests such as didymo establishing in the North Island.

The Check, Clean, Dry crew are available to come and talk to groups, set up displays at your event or to support cleaning stations for sporting events in and around freshwater spots in our region. If you would like to arrange a visit from the crew or some professional development for your staff to deliver effective freshwater and Check, Clean, Dry advocacy, then contact us.

You too can become an advocate for protecting our freshwater resources by joining team Check, Clean, Dry. Ask one of the crew members to sign up to the Check, Clean, Dry pledge.

For the best cleaning methods for your gear and the latest information to prevent freshwater pests spreading click here.

Report a pest / get advice

Not sure if you’ve identified a weed? Need to know how to deal with a pest? Our pest management team wants to hear from you. Our pest management role includes providing advice to the public. If you are having problems with pest animals or plants we can offer advice on control options.


Contact the team