Final report

Project objectives

Clover Root Weevil has been around since the mid-1990s. Feeding exclusively on clover, adult CRW eats clover leaves, and the larvae feed on stolons, roots and nodules. It has a major impact on clover production and survival, and reduces the ability of clover to fix nitrogen. Clover can be totally removed from the pasture - and the valuable contribution to feed quality clover makes in its own right. Clover requires nitrogen to maintain growth and survive. Farmers had found that applying N-fertiliser in small doses after grazing keeps the clover growing - but this had not been scientifically trialed to any extent.

The project sought to provide management solutions for pastoral farmers struggling to maintain clover in their pastures and profitability in the presence CRW, to develop and trial nitrogen fertiliser strategies to enhance clover in the presence of CRW, to assess the contribution of nitrogen by clover fixation in the presence of CRW, and to ensure that relevant information was shared with farmers as soon as possible. Six objectives were detailed in the original application:

Objective 1:

Collate available information on CRW and identify technology transfer champions in the regions.

Objective 2:

Identify fertiliser and pasture agronomy strategies that alleviate the impact of CRW and target maintaining farm profitability.

Objective 3:

Clover re-establishment in CRW infested areas.

Objective 4:

Develop scenarios for a series of management options for farming in the presence of CRW.

Objective 5:

Develop and disseminate a ‘tool box' of pasture management options for farming with CRW.

Objective 6:

Project management - getting the skill set to get things done right.

During the course of the project there have been a number of staff changes with AgResearch, the science provider. This has inevitably altered the emphasis placed on certain components of the project. In addition to staff changes, the (largely) successful release of a biocontrol option for CRW (the biocontrol has not established in Northland) led to less emphasis placed on Objective 4 - development of scenarios for management options.

Challenges with management of 2 of the 3 N fertiliser field trial sites saw the quality of data seriously compromised, with one site abandoned in May 06 after only 6 months of data collection, and the second one abandoned in June 07. The 06/07/08 droughts also severely affected the demonstration sites, limiting the reliability of recommendations made on the basis of this project.

The proposed "toolbox" for dissemination of information about management options has translated into a water proof pamphlet looking briefly at issues around CRW and also aiding the identification of other pasture pests that may be around, and a revamping of the Clover Root Weevil website. These are discussed in more detail in section 4a.

Approach

The project proposed collation and dissemination of information already available on CRW, field trials to identify fertiliser and pasture agronomy strategies that alleviate the impact of CRW and target maintaining farm profitability, economic analysis of a range of responses to CRW, ongoing assessment of options for re-establishment of clover into affected pasture and considerable dissemination of the results of the project.

The initial collation of information was carried out, and is contained in the report "Managing Clover in the presence of Clover Root Weevil - A summary of current knowledge prepared for New Zealand farmers (2006). B. Willoughby and H. Eerens." In addition to providing the basis of information for project Governance Group members and other key regional contacts, this report provided the basis for much of the content of the website developed by the project.

A field trial was undertaken at three dairy farm sites in the Waikato to compare pasture responses to four experimental rates of urea under two contrasting grazing management regimes. The trial layout was four rates of nitrogen (0, 100, 200, and 400 kg/ha/year) replicated four times in a randomised block design. Each plot was split in two and randomly allocated one of two ‘pasture management' treatments (Optimal and Conventional) giving a total of 32 10 x 15 m subplots.

Additional demonstration trials were established in the Northland, Waikato, Bay of Plenty, Taranaki, Manawatu, and Hawke's Bay regions commencing spring 2006. They were laid out in a randomised block design with two blocks (Optimal and Conventional clover management treatments) and four N input treatments. Trial size varied to encompass whole paddock (excluding any atypical areas) and plots were as equal sized as practical. All trial sites were part of the normal grazing round and used for conservation or set stocking.

Re-establishment trials were set up by a previous Northland Clover Pest Interest Group project to investigate the benefits of removing clover root pests and diseases through the use of a break crop on subsequent pasture establishment. The trial was established in April 2004 on the property of Richard Henderson, a dairy farmer at Horsham Downs, near Hamilton. Three paddocks had been selected as sites, each with the same volcanic soil (Hamilton clay loam) but with contrasting pre-sowing conditions namely Turnips, Maize and Pasture. Five grass treatments were sown and each site was marked out in 12 × 15 m plots in a 5 × 6 grid giving a total of 30 plots.

The resultant pastures were assessed for composition and production and the data were used in the Farmax® and Udder™ farm decision programmes to determine the long term economic benefits. While CRW can reinvade within a year, nematodes and root diseases reinvade more slowly, and therefore the clovers are more robust and can tolerate CRW damage when a crop is included in a pasture renewal programme. Cost benefit analysis showed economic benefits from inclusion of a maize or turnip crop compared to grass to grass establishment.

What were the main findings from this project?

Economic Cost of CRW

A review of the studies on the impact of CRW on white clover dry matter production has shown that losses over the medium term were generally in the range from 18-35%. If a "do nothing" approach is adopted, the weevil could potentially cost the pastoral economy around $400 million a year.

Economic assessments at farm system level using decision support models showed that farm gross margins would fall by 10-15% with that do nothing approach.

The advice that the action group has received is that a combined approach is required to maintain healthy and productive clover in the presence of CRW.

Fertiliser and pasture agronomy strategies

Firstly, applying small amounts of nitrogen fertiliser after grazing in spring and autumn can help clover withstand CRW larval attack (on roots and nodules). The appropriate quantities of N will vary with the individual farm nutrient management plan.

A field trial was undertaken at three sites to compare pasture responses to four experimental rates of urea (0, 100, 200 and 400kg N/ha/year) under two contrasting grazing management regimes. The main recommendations that can be drawn from this research are:

  • Be aware that using high rates of N fertiliser may increase pasture vulnerability to drought.
  • Even when using N fertiliser, clover content can be lifted by aiming for low post-grazing residues in spring, autumn and winter. This prevents shading of white clover by grass to maximise clover growth.
  • Higher post-grazing residues should be maintained in summer, to provide protection for the clover growing points from the summer elements.
  • Although there was insufficient data to make a firm recommendation on the preferred N application rate in the presence of CRW, the 200kg/ha/year performed well at one site in terms of pasture production, N fixation and weed content.

The researchers also suggested a lower overall annual rate (e.g. 150kg/ha/year) applied in split dressings after grazing from mid-autumn to late spring. This might be economically and environmentally more sustainable since it may also increase overall clover content by shifting the competitive balance between grass and clover pasture components in clover's favour during the summer. Based on 2007 figures, provided pasture N response is in excess of 15kg DM/kg N, the 150kg/ha will be enough to restore farm gross margins (estimated to fall 10-15% after severe CRW attack).

Pasture re-establishment

Pasture renovation using a non-host plant break crop such as brassicas or maize, removes pests such as CRW and nematodes so clover can be re-established into a "clean" site.

A paddock-scale field trial has shown that two-year-old pasture following a maize or turnip crop had more clover, fewer weeds and higher autumn production compared to pasture following grass-to-grass establishment.

On farm scale, using 2007 costings this equated to gains of $106-$108/ha for a central North Island sheep and beef farm where pasture was renewed after a crop, and the crop area was optimised to fully utilise pasture. In comparison, grass-to-grass re-establishment resulted in more modest benefits ($53/ha).

Similar outcomes were shown for a typical Waikato dairy farm with gains of $490-$541/ha for pasture for pasture established after crops compared to $336/ha for grass-to-grass renewal. Overall, two year old diploid perennial ryegrass pastures (eg Bronsyn) had more grass and less clover than tetraploid perennial ryegrass pastures (eg Quartet). There were no differences in total pasture production in spring, but the diploid pastures had higher production than tetraploid in summer and autumn.

The farm decision programmes (Farmax and UDDER) indicated it was most economically beneficial to use diploid ryegrass in the North Island sheep and beef farm and tetraploid in the Waikato dairy farm.

How were the results of the project disseminated?

Sharing information on the impacts of Clover Root Weevil and strategies for maximising production in the presence of this pest has been a key component of the project. Assisting newly affected farmers to come to grips with the potential impacts of the pest and assisting them to maintain production has been a long term aim of the Action Group.

The main outputs for dissemination of the results of the project are the recently produced pamphlet and the revamped website. The pamphlet was printed on water proof paper, and is intended to double as a field guide to pasture pest larvae. The website continues to be hosted on the NZ Landcare Trust website, which brings advantages when content updating is required. It covers background information, aids for identification of CRW damage in pasture, its impact on nitrogen fixation, strategies for farming with CRW and basic information about the biocontrol. AgResearch is ensuring that the pamphlet and associated information is given to farmers as they receive samples of the biocontrol wasp. Indications are that the biocontrol works best on healthy clover - as covered in this pamphlet.

A number of dissemination opportunities have been undertaken throughout the term of the project, including:

  • Northland Agricultural Field Days at Dargaville
  • National Field Days at Mystery Creek in Hamilton
  • Presentation to Landcare Trust conference, Wellington
  • Media articles in various rural media
  • Targeted field day in the Waikato.

Final dissemination of the outputs of the project:

  • NZIPIM onLINE email newsletter, 9 December
  • Paper submitted for presentation at NZ Grasslands Conference, Northland Nov 09
  • Media articles - Country-Wide, Dairy Exporter, Straight Furrow, local papers
  • Input into Rural Delivery programme - under way (March 09).

Landcare Trust staff in Whangarei, Nelson and Southland are utilising opportunities to ensure that the outputs of this project continue to be available to farmers well into the future.

What difference has this project made?

It is anticipated that the project results will significantly support farmers exposed to CRW impact for the first time. Information such as this, prepared with input from farmers for farmers will help farmers maintain production as high as possible despite the presence of CRW. This is particularly relevant as CRW appears to be spreading further throughout the South Island.

Due to the limitations of the trial site results (a function of a number of factors as previously detailed, including the drought conditions which were obviously beyond the control of the project team), the recommendations for nitrogen requirements of pasture in the presence of Clover Root Weevil that were originally intended to be developed do not have the confidence anticipated. None-the-less the results that were obtained support the observations that well managed pasture is better able to remain productive in the presence of CRW.

Major outputs from the project

  • Publications (booklets, posters, links to websites) All of these are available on the Clover Root Weevil website: http://www.landcare.org.nz/publications/websites/clover-root-weevil/more-information/
  • Managing Clover in the presence of Clover Root Weevil - A summary of current knowledge prepared for New Zealand farmers (2006). B. Willoughby and H. Eerens.
  • Investigation into fertiliser and pasture agronomy strategies that alleviate the impact of clover root weevil. PJ Gerard, TE Eden, DJ Wilson, SA Howlett, and JPJ Eerens. August 2008
  • Economic and Production Impacts of Clover Root Weevil on New Zealand Farming. Pip Gerard, Duncan Smeaton, Han Eerens and Sally Howlett. May 2007
  • Cost benefit analysis of clover re-establishment options in the presence of clover root weevil. Pip Gerard, Rex Webby, Duncan Smeaton, Tina Eden, Sally Howlett and Han Eerens. October 2007
  • On Farm Management of the Economic and Environmental Impacts of Clover Root Weevil. PJ Gerard, TE Eden, DJ Wilson, SA Howlett, JPJ Eerens and MWA Slay. August 2008
  • Press release - Prepared by Hugh Stringleman for dissemination to Country-Wide and other local papers as appropriate. Printed in April edition of Country-Wide.
  • Popular article - "Clover root weevil and biocontrol: What's happening at the research front?" prepared by Pip Gerard. Article included SFF project outcomes and was published in Dairy Exporter, Straight Furrow and newspapers.