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Clover Pest a $500m Problem

Clover Pest a $500m Problem

A major pest that is costing pastoral farming an estimated $150 million per year may become a $500m per year burden within a decade, according to an economic analysis carried out for MAF Biosecurity last year.

Clover root weevil (CRW), a small bug that feeds on white clover, is dramatically reducing clover growth and nitrogen fixing ability. The plant that is nutritious for livestock is also a vital source of nitrogen for other pasture species. Farmers rely on it for their main competitive advantage – low-cost feed.

However, the past decade has seen some radical changes in pasture composition. Many paddocks that once were 30% clover are now down to 5%. In others, the clover has a sickly yellow hue instead of its normal bright green.

Dry matter production has fallen by a third on some farms, and farmers have had to increase the use of feed supplements and fertiliser nitrogen to plug the widening gap between stock feed requirements and pasture supply.

CRW is not the only cause of white clover’s decline, but it is certainly a major one. It
was discovered on Waikato farms ten years ago and since then has spread to most areas of the North Island and to parts of the South Island. Within a few years it is likely to be found from North Cape to Bluff.

There is no known way of eradicating it nor any sure way of controlling it, and although promising work is now being done on parasites and the development of more tolerant strains of clover, these projects will take some time to complete and are unlikely to be a complete solution.

Some Waikato farmers have spent years trying to find ways to manage their situation and maintain profitability. Several years ago, with the assistance of the NZ Landcare Trust, they set up an action group to share information and identify the problems that needed answers.

Dairy farmer Lorraine Bilby, head of the group at the time, says that when production on her property had dropped by a third she tried various fertilisers without success before finding a solution.

"Several farmers had identified that if you used strategic applications of urea to replace the nitrogen that clover was no longer fixing, you could get both a clover and a grass response,” she says.

"I had vowed that we would never used nitrogen on our property but with CRW infestation we couldn’t grow enough grass to stay in business, so we started putting nitrogen on often and in very small quantities, and made up the production we had lost."

Frequent light applications of nitrogen have been criticised as potentially increasing water pollution, but farmers believe that the small amounts are fully used by plants and do not constitute a hazard. The total amount of nitrogen per hectare is no different, just the source.

Finding environmentally sustainable ways of using fertiliser nitrogen was one of the areas the group identified as needing research. Last year they formed a national farmer body – the NZ Clover Root Weevil Action Group – to try to make it happen and to pass their experience with CRW on to other farmers.

Through the NZ Landcare Trust, the national Group applied successfully to the MAF Sustainable Farming Fund for research grants, and regionally based projects are now under way. Dr Nick Edgar of Landcare, manager of the research programme, says that the aim is to develop a “toolbox”of pasture management options for farmers having to deal with CRW infestation.

“We are establishing plot trials on representative farms in regions of the North Island to fine tune the recommendations for each area, and demonstrate sustainable farming practices,” says Edgar.

“We need these data to adjust nutrient management plans to take account of nitrogen used on weevil infested pastures, and to determine the best ways of re-establishing clover where necessary.”

Getting information out to farmers is vital, and the Group is identifying individuals in each region to champion the cause. One is Ian Armstrong, a Taranaki dairy farmer, who discovered last year that CRW was devastating his clover.

“It really hasn’t hit home yet just how much clover we have lost in this region. Farmers are complaining the cows are simply not producing and blaming it on all sorts of things,” he says.

“Learning from the Waikato experience has certainly helped me maintain pasture growth this year, but we need an overall strategy to find more sustainable methods in the longer term.”

In the meantime, farmers who still have clover in their swards can improve the situation by managing pastures in ways that favour clover. Research in the Waikato has shown that vigorously growing clover is more tolerant to CRW.

This approach has certainly worked for Waikato dairy farmer David Wilson who uses careful grazing management to ensure the long life of his pastures, and has fared better than many others affected by CRW:

- Keeping the pasture leafy in spring but avoiding the shading out of clover

- Avoiding overgrazing in summer as this devastates clover

- Adequate subdivision to allow good grazing control

- A stocking rate that suits the property and the pastures ie. avoids overgrazing in summer and excessive pugging in winter.

Bruce Willoughby, an AgResearch entomologist who has been studying CRW on the Wilson farm, says the measures have resulted in an excellent environment for clover growth.

“The pasture plants are highly tillered and well anchored to the soil, there is a dense root mass that resists pugging, and the soil is in very good condition,” he says.

“Farmers will benefit greatly from using good clover management practices, and there is plenty of information available on them.”

Nick Edgar says that results from the farmer-driven research programme will be tailored to each region and made available through field days and the local media as well as from the NZ Landcare Trust and the MAF Sustainable Farming Fund.


For a copy of the CRW Action Group’s leaflet “Managing Clover in the Presence of CRW”, phone 07-838-5031


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