Southland clover crisis eased by fast response

One million tiny insects will make a huge economic difference to the Southland region, thanks to the joint efforts of AgResearch, Beef + Lamb New Zealand, DairyNZ and Environment Southland.

Last year’s mild winter has meant that clover root weevil has taken its small foothold on the farms of Southland to a widespread infestation that has had a huge impact on the production ability of the region’s pastures.

The industry partners considerably accelerated a project, which had been releasing parasitised clover root weevils on Southland farms for some time.

“AgResearch teams collected 400,000 parasitised clover root weevil from farms in Canterbury during autumn and facilitated the collection by farmers of an estimated 250,000 from the Invermay farm,” says AgResearch pest specialist and scientist Colin Ferguson.

“These were released on 1,000 Otago and Southland farms prior to winter. AgResearch’s ability to rapidly redirect some of its Core Funding was critical in enabling this fast response.”

Based at AgResearch’s Invermay campus, Mr Ferguson has seen the damage wrought by the weevil on Southland farms first-hand.

“The clover root weevil has been present in Otago and Southland since 2010, but large numbers were present in only a few locations.” he says.

“That was until last year – what we didn’t need was the 2013 very mild winter. The mild conditions allowed a greater number of clover root weevil eggs to hatch and more of the larvae survived right through the winter. As a result the population of the weevil just exploded.

“Tremendous pressure was placed on pasture from the increased numbers of larvae that fed on the clover roots and their nodules over winter. That damage was followed by the large population of adult clover root weevil emerging in early summer and feeding on the cloverleaf. Normal spring and summer grazing of clover added to the stress on already struggling plants.

“Affected farmers were either seeing clover that disappeared very quickly once grazed or a complete absence of clover plants in their pasture. Without clover farmers can’t fatten lambs and those that are looking to overwinter dairy grazers can’t do that. It is having a huge impact on farm returns right now.”

The solution to this difficult situation came in the form of a tiny parasitic wasp from Ireland.

The Irish wasp is a highly effective bio-control of clover root weevil. AgResearch scientists have seen reductions of greater than 90% of the clover root weevil population in monitored North Island farms where the wasp has been released.

AgResearch scientist Dr Scott Hardwick led the Lincoln-based clover root weevil collection team.

“We literally vacuumed up weevils from Canterbury farmland where the bio-control wasp was already hard at work and placed them in packs of 100 for Southland farm release,” he says.

“The result is a significantly accelerated spread of the bio-control and the process of clover recovery has begun.

“Southland farmers can expect clover content to return to stable levels two to four years after the wasps’ arrival on their farms.”

Beef + Lamb New Zealand, DairyNZ, Environment Southland and AgResearch worked together to ensure that the farms selected as release sites had the maximum impact for the region and that farmers were provided the information on how to manage through CRW infestations.

Mr Ferguson advises farmers to be patient.

“Although things are going to be tough for the next few years farmers will get through this with the help of the bio-control,” he says.

“North Island farmers have already gone through this process and clover root weevil is not much of an issue now for any of them.

“If we had let things run their natural course the Irish wasp would have continued to spread down the South Island, following the clover root weevil, and eventually arrived everywhere in Southland. These actions by the industry this autumn will considerably speed up this process and make a huge economic difference to Southland.”

AgResearch teams are continuing the collection and distribution of parasitized weevils, aiming for a total of 1,000,000 over two years, funded through AgResearch Core Funding.