Few realise it but Northland is a battleground for a 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.
Biocontrol is not designed to totally eradicate an individual species, but to keep pest populations at low levels. NRC invests $50,000 a year in biocontrol and is part of a wider collective of 13 other regional councils and the DOC. Collectively, group members fund a national biocontrol programme of about $670,000 annually. This is managed on behalf of the collective by Landcare Research, who provide for research, quarantine facilities, management, and releases of the agents within New Zealand. In 2007-08, the collective supported research into agents for 15 pest plants, 12 of which are significant pest plants in Northland.
Before bio agents can be released into New Zealand, there is a rigorous process of trial and experimentation overseen by the Environmental Protection Authority (EPA). Imports are strictly controlled via a process that includes public debate and scientists can often take several years to satisfy the risk assessment criteria and complete 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.
Several agents have been trialed in Northland for the control of gorse. The English gorse thrip was released in the nineties however did not survive in the region. Trials of the hardier Portuguese gorse thrip are ongoing.
There are now five bio agents that attack ragwort and one of these, the ragwort flea beetle, has proven very effective in Northland. This tiny beetle is a root and crown feeder and is now commonly found in most areas.
In October and November 2007, releases of the boneseed leaf roller were undertaken in Northland. Monitoring of release sites has shown that small populations are surviving and it is hoped that this agent will work well.
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 was once common throughout Northland, occupying the margins of most Northland waterways and many wetlands. Since the introduction of the bio agents, the presence of mistflower has declined markedly.