He aha te mana koiora?

What is biocontrol?

Pest plant biocontrol is the act of introducing a natural enemy to control a pest plant. These natural enemies are either insects or pathogens. Once released in a new region, they are referred to as ‘biocontrol agents’.

Biocontrol agents controlling pest plants in Tāmaki Makaurau / Auckland

Many biocontrol agents have been successful at controlling their host plants in Tāmaki Makaurau / Auckland. For example, ragwort used to be widespread across the region. The introduction of the ragwort flea beetle led to a huge reduction in ragwort across the region. A result manual control alone could not achieve at that scale. 

Other biocontrol agents also active in the region, include; 

  • mistflower rust fungus
  • tradescantia yellow leaf spot fungus
  • tradescantia leaf beetle

Biocontrol is a long-term method, not a quick fix. Here's what to expect:

  • Years 1–2: Insect or pathogen establishes at the release site 
  • Years 3–5: Populations grow, damage to pest plant becomes visible 
  • Years 5+: Pest plant becomes easier to manage alongside other method 

 

Biocontrol benefits

  • Long-term sustained control of the pest plant to low densities.
  • Native flora regeneration and improved biodiversity at site.
  • Cost-effectiveness.
  • Reduced reliance on herbicides.
  • Overall reduction in the dominance and impacts of widespread pest plants in the region. 

 

Biocontrol safety

Each potential biocontrol agent is subject to years of testing to ensure it is safe to release. This includes examining whether it will feed on desirable plants or have any negative interactions with other native insects or birds. The Environmental Protection Authority (EPA) must approve every release, through a process that includes public consultation, iwi engagement and consideration of mātauranga Māori.
 

See the EPA website for information about the process of safely bringing a biocontrol agent into Aotearoa.

 

If you find a biocontrol site don't disturb it

Always look for biocontrol signage before starting any pest control work (herbicide or manual). If biocontrol is in place at a site, it’s essential to leave that site uncontrolled with other methods (herbicide or manual). This is the most important thing the public can do.  

If biocontrol is happening at a site: 

  • don't spray
  • don’t pull weeds or remove any parts of the pest plant 

Removing the pest plant removes the food source for the beetles or other biocontrol agents causing them to die off. Other types of disturbance can reduce the biocontrol agent’s ability to control the pest plant. If you're a community group working on public land and you're not sure, contact us first: pestfree@aucklandcouncil.govt.nz