One of this country’s most serious pasture pests has now been discovered in southern Wairarapa.

Sitona lepidus, or clover root weevil, feeds on white clover destroying its ability to fix nitrogen to maintain soil fertility.

Adult weevils were found ‘by chance’ during routine sampling of local pasture by AgResearch staff as part of a Sustainable Farming Project investigating the benefits of biological control of another introduced pest, Argentine stem weevil (ASW). 

The project looks at the benefits of biological control of the ryegrass pest in association with new endophyte-ryegrass cultivars.

AgResearch Entomologist Mark McNeill says at this stage the clover root weevil appears to be restricted to an area south of Featherston.

A brief survey on farms near Masterton, Martinborough and Greytown did not find the weevil.

He says the limited distribution suggests the weevil, which is very mobile, may have come down from either Hawkes Bay or Manawatu in transport trucks, cars or agricultural equipment.

Clover root weevil is an accidentally introduced pest in this country.

First discovered in the Waikato in 1996, it has been moving its way though the North Island.

It is already a significant problem in the North Island where clover content typically has declined from an average 20% to 10% because of the weevil.

Conservative estimates suggest it could cost around $300 million a year in lost productivity and profitability across the whole country. Clover root weevil is eventually expected to reach the South Island.

That does not take into account environmental damage from increased run-off into waterways of higher levels of Nitrogen fertiliser farmers in infested areas now have to apply, to counter the loss of ‘natural’ nitrogen the clover would normally put into the soil.