Biological control
Biological control in Northland
Few realise it but Northland is a battleground for a little-known and largely unseen war between a host of tiny insects and fungi and some of the region’s worst weeds.
In the last five years alone, 49 releases of different ‘biocontrol’ agents have occurred in Northland to help control weeds such as Californian, nodding and scotch thistles, alligator weed, broom, gorse, mistflower, and ragwort.
How do they work?
Don McKenzie, our Biosecurity Team Leader explains what biological control is all about and how it is used in Northland.
Biological control is the control or regulation of pest populations by their natural enemies, which are usually – but not always - insects.
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Don McKenzie, Biosecurity Team Leader for the Northland Regional Council.
The ranks of the environmental ‘good guys’ currently doing battle against a variety of plant nasties in Northland include not only sap-sucking mites and some beetles with a taste for plant roots, but also a fungus.
Biocontrol is not designed to totally eradicate an individual species, but aims at keeping pest populations at low levels.
This tactic has already proven its worth when controlling some of the worst weeds and the future of biocontrol definitely looks promising for Northland.
How much do we spend in Northland on biological controls?
The NRC invests $50,000 a year in biocontrol and is part of a wider collective of 13 New Zealand Regional Councils and the Department of Conservation. Collectively, group members fund a national biocontrol programme to the tune of about $670,000 annually.
This is managed on behalf of the collective by Landcare Research and provides for research, quarantine facilities, management, and releases of the agents within New Zealand.
How do we know biological controls are safe?
Before bio agents can be released into New Zealand there is a rigorous process of trial and experimentation overseen by the Environmental Risk Management Agency (ERMA).
Imports are strictly controlled via a process which includes public debate and scientists can often take several years to satisfy the risk assessment and trial work.
When biocontrol is decided upon as an option, one of the first steps in the process is to see if the weed has any natural predators in New Zealand and/or overseas. Potential agents are then studied further either here or overseas to evaluate impacts on non-target species before they are introduced.
The situation in Northland
We work closely with the Department of Conservation and the public to assist with the introduction, and on site monitoring, of the biocontrol agents and nationally there are now biocontrol agents available for 20 weeds, with research currently underway into many more.
In the last five years alone, there have been 49 releases of different biocontrol agents in Northland to control a myriad of weeds. This year the collective will support the research into agents for 15 pest plants, 12 of which are significant pest plants in Northland.
Included are moth plant, woolly nightshade, tradescantia (wandering jew), broom, banana passionfruit, Japanese honey suckle, boneseed and alligator weed.
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Adult Boneseed Leaf Roller.
Additionally, releases of new agents to target boneseed (the boneseed leaf roller) and gorse (the gorse soft shoot moth) are to be carried out in Northland in October and November of 2007.
Biocontrol has definitely boosted the control of both agricultural and environmental weeds within Northland.
There are now five bio agents which attack ragwort and one of these, the ragwort flea beetle, has proven very effective. This tiny beetle is a root and crown feeder, is now commonly found in most areas and provides excellent control providing overgrazing is avoided.
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A Northland paddock boasts a healthy – and very much unwanted – crop of ragwort in this file photograph. Scenes like this are far less common than they once were due to ragwort biocontrol agents, particularly the ragwort flea beetle.
One of the region’s most successful biocontrol releases over the past five years has been the release of a gall fly and a smut fungus to control mistflower.
Mistflower (not to be confused with the similar looking but larger leafed Mexican devil weed) was once common throughout Northland, occupying the margins of most Northland waterways and many wetlands.
This weed can dominate open damp sites and prevent regeneration of any other species.
Since the introduction of the bio agents, the presence of mist flower has declined markedly. Although the small white flower can still be seen at this time of the year signalling the weed hasn’t been fully eradicated, population levels have been drastically reduced. Another well-known weed, gorse, now has eight bio control agents.
Many of us will have seen the gorse spider mite which forms a conspicuous white web about the size of an adult’s fist on green gorse foliage.
The mites suck the sap of the gorse bush and cause obvious damage when their numbers build up. Persistent damage can be limited by predation of the mite by other insects.
Meanwhile, other gorse biocontrol agents like the gorse pod moth are becoming more common and are spreading well; this particular agent is showing good potential to destroy gorse seeds in springtime.
Future developments
Overseas studies by Chinese scientists have found a fungus which is effective against alligator weed and New Zealand researchers have short-listed a range of species in Brazil to control tradescantia.
A host-specific beetle has caused impressive damage to tradescantia both in the laboratory and in the field.
Research is also under way to track down potential agents to control moth plant and Japanese honeysuckle.
Moth plant is a rampant and difficult to control weed in Northland and when herbicide and non chemical means of control are clearly not a long-term solution, investment in biocontrol research makes strategic sense. Early feedback is that Landcare staff are confident of finding suitable bio control agents for both moth plant and Japanese honeysuckle.
Given the current research prospects and recent discoveries overseas we believe biocontrol has a growing part to play in the effective control of weeds into Northlands future.