Weevil research in race against time

By Philippa Stevenson

It is little consolation to farmers, but a tiny pest threatening their low-cost grazing system - New Zealand agriculture's major competitive advantage - has had a year as difficult as their own.

The clover root weevil gnawing its way through valuable clover pastures from Te Kuiti to Whangarei has suffered as much as grass and stock in the summer's dry conditions.

However, AgResearch scientist Dr Pip Gerard said the pest would also respond quickly to the recent rain.

"If conditions are good for farms to grow clover it's good for the weevil," she said.

Fellow AgResearch scientist Dr Jim Crush said the weevil raised farmers' overheads by devastating the nitrogen-fixing clover that underpinned New Zealand's low-cost-grazing system.

Estimations of farm costs from weevil-damaged pasture have included around $90,000 a year in lower milk yields and $13,000 a year for replacement nitrogen.

In the past two years, a major research effort with industry and Government backing has targeted the spreading invader first discovered in the Waikato and Bay of Plenty in 1996.

Four producer organisations - dairy, meat, wool and deer - have provided funding of $1.4 million over four years.

"Progress [in research] has not been limited by funding. What we need is time," Dr Crush said.

Scientists were starting from a "zero base" of information because although the weevil was a native of Europe, and also widespread in North America, it was not a serious pest there.

He said farmers anxious for answers were making a major contribution to the research effort.

In trials to find clover species which tolerated the weevil, 40,000 clover plants were being grown on Waikato and Bay of Plenty farms with the owners' cooperation.

Dr Crush said a series of six field days beginning on Wednesday would be as much about telling farmers what researchers knew as obtaining on-farm experience of the pest.

"Farmers' ideas and observations are very important. If we can get a partnership going with good robust, sensible farmer input it will be very valuable," he said.

"There is no magic-bullet solution. It will be a package and it has to be acceptable farm management. We need to know whether we are following the right track."

Dr Crush said a three-pronged control strategy could include clover which the weevil found less palatable, and which grew better after attack.

Managing pasture so that it was not over-grazed, or lacked moisture or fertiliser, was also likely to help the clover to resist or recover.

Dr Gerard said bio-controls such as parasites or fungi had potential but were unlikely to be available within five years.

AgResearch has contracted researchers in Europe and America to search for weevil predators but the most promising find has been a native New Zealand fungus which has had high weevil kill rates in laboratory studies.

* The field days are being held on farms in Warkworth, Te Aroha, Huntly, Morrinsville, Te Puke and at the Ruakura Research Centre, Hamilton.