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Clover Root Weevil Discovery in Gore

Wednesday, 10 March 2010 03:16 p.m.

Clover Root Weevils have been found at several sites around Gore, confirming fears that the tiny pest would migrate to Southland and attack the region’s pastures.

Environment Southland discussed the implications of the discovery at today’s Regional Services Committee meeting, with Councillors dismayed to learn that even a moderate infestation is likely to reduce annual clover production by 1000kg of dry matter per hectare. Scientist Colin Ferguson from AgResearch at Invermay said the annual cost to the national economy was estimated at $1 billion.

The weevils have the capacity to remove clover from pasture altogether, which would require farmers to use synthetic nitrates to maintain production. “Looking at the numbers we have found around Gore, this time next year farmers are going to notice significant damage to their clover,” Mr Ferguson predicted. Each weevil lays up to 3000 eggs, so the population would skyrocket.

The only hope of controlling the invasive pest rests with its natural predator, a parasitic wasp imported from Ireland and bred by AgResearch.
The Council will seek to partner with Landcare Research, and farming stakeholders such as Meat and Wool NZ and Dairy NZ to initiate a biological control programme that could start as early as next spring.

Mr Ferguson said that if the parasitic wasps could be introduced into Southland at the same time that the weevil was becoming established, there was a good chance of limiting the impact on the region’s clover.

Environment Southland Biosecurity Manager Richard Bowman said that the Landcare Trust was keen to coordinate an initial release in Southland with a farmers’ group likely to be established as a means of applying for government funding and holding field days to spread the word in the region.
The first field day is planned to be held at the Gore Showgrounds on 7 April.

There was no chance of stopping the weevil’s natural spread. Aside from their natural ability to disperse, they were “very good hitchhikers” with their movement linked to human activities. Clusters of infestation had been spread from A&P Showgrounds, with weevils found on stock, hay, farm machinery and vehicles.

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