Clover is still disappearing from Otago and Southland paddocks as the clover root weevil continues to spread throughout the South Island.
About 30 farmers attended a Beef and Lamb New Zealand workshop in Riverton last week to receive the parasitoid wasp (Microctonus aethiopoides) that is being used throughout New Zealand to combat the clover root weevil.
This weevil was introduced to New Zealand in the early 1990s and was found by accident in 1996 in Waikato and in Auckland.
AgResearch scientist Colin Ferguson said it was first believed the clover root weevil was a weevil that attacked lucerne.
The adult clover root weevil prefers white clover but feeds on other types of clover as well. The larval stages feed on clover roots. Young larvae tend to feed in clover root nodules (which capture atmospheric nitrogen), while bigger larvae will feed anywhere on the root system.
Mr Ferguson said the adult weevils would become very common in pastures during the next few weeks as the larvae began to hatch.
''They will start to appear in the pasture in huge numbers.''
In severe cases, the clover root weevil could destroy clover, but was more known for targeting the plant's root nodules, reducing its ability to fix nitrogen.
The parasitoid wasp Microctonus aethiopoides, which is also known as the Irish wasp, was introduced to New Zealand in 2006 as a biocontrol agent for the weevil.
The wasp lays one egg into one weevil. It releases venom which makes the weevil infertile so it can not lay eggs or produce sperm.
When the wasps hatch the host weevils dies and the cycle continues.
Mr Ferguson and the team at AgResearch had been working with Beef and Lamb New Zealand and PGG Wrightsons seeds division staff since March last year introducing the wasp throughout the South Island.
He had found most farmers wanted to work to control the clover root weevil but some still believed the pest was not on their property.
''They tend to come on board very, very quickly.''
The workshops were being held throughout Southland and wasps were being distributed to farmers from throughout the region.
Mr Ferguson said the next step was for AgResearch and Beef and Lamb New Zealand to identify places were the wasp was not present and then release it into those areas.
''If the wasp wasn't everywhere in the next two years I would be surprised.''
If farmers were interested in obtaining the wasp, they could contact AgResearch.