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Clover Root Weevil: A major problem for NZ - How to minimise its costs for farmers [PDF 258KB]

Updated: 28 May 2009

Project description

The project seeks to provide management solutions for pastoral farmers struggling to maintain clover in their pastures and profitability in the presence CRW. It will develop and trial nitrogen fertiliser strategies to enhance clover in the presence of CRW, and assess the contribution of nitrogen by clover fixation in the presence of CRW.

The issue/opportunity

Clover root weevil (CRW) is now present throughout most of the North Island, and is likely to also establish in the South Island. CRW only attacks clover and with CRW populations in NZ ten times higher than those experienced overseas management issues here are unique. On-farm evaluation of clover varieties seeks to identify cultivars that cope better with the additional stress applied by CRW. The introduction of a biological control agent, currently funded by industry sources, is likely to result in the release of a parasitic wasp later in 2005, pending approval from ERMA. However it is not anticipated that either of these will provide a single solution to CRW. Development of tools for on farm management of the economic and environmental impacts of clover root weevil will remain a critical component of any strategy.

Context/background

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 have found that applying N-fertiliser in small doses after grazing keeps the clover growing – but this has not been scientifically trialled to any extent.

Methods

The project will comprise 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 farmer education underpinning the entire project.

Latest update

The goal of SFF project 05/085 is to compare and cost a range of pasture establishment and management regimes in order to develop scientifically-based recommendations of how to best manage pasture in the presence of the weevil. The key component that underpins all the objectives is farmer education, and to this end, the project culminates in the production of a ‘toolbox’ that can be distributed to farmers to assist them in their decisions.

Small plot trials were established in the Waikato to compare four N fertiliser rates (0, 100, 200 & 400 units N) and two grazing regimes (optimal & conventional) on clover growth in CRW infested pastures. Interim results were described in the previous progress report. Prior to the last governance meeting, the management group was informed that a breakdown in communication between the farm owner and farm manager on Holmes’ property (Tauhei) had resulted in over-application of nitrogen at this trial site. Since spring 2005, contractors have applied 300 units N to all plots in addition to the trial treatments. Consequently, it is now not possible to compare the results from this site with those from Wilson’s property (Hoe O Tainui). It was proposed to investigate the feasibility of re-focusing the research effort at Holme’s property to monitor N depletion rates from the high levels now present to more realistic levels. AgResearch are following this up with agronomists and a decision is pending analysis of soil samples. Routine sampling has continued at Wilson’s property and the annual application of 15N has been completed.

Paddock evaluations are continuing as part of the N fertiliser trial research. The paddock evaluations complement the small plot trial work in the Waikato. Five regional demonstration sites are located in the North Island. At each site, plots are managed either “conventionally” or “optimally” (i.e. in a manner expected to optimise clover growth and persistence). Evaluations commenced in spring 2006 and the first annual samples were taken by teams from AgResearch during June 2007. Invertebrate counts from assessment of soil cores are almost complete and data will be analysed shortly.

A replicated clover re-establishment trial in the Waikato has been undertaken with the aim of assessing the cost of different pasture renewal options in CRW-infested areas against the longer term benefits. . It was established in April 2004 on the property of R Henderson, Horsham Downs. Three paddocks had been selected as sites, each with contrasting pre-sowing conditions namely: turnips, maize, or pasture. The trial was assessed in two stages, firstly seedling establishment and secondly, pasture production and quality two years after establishment. The following analyses are based on three seasonal pasture assessments in 2006 and 2007.

Whilst the site that had previously been in turnips produced more clover than the grass site in spring, this was not sustained to the same extent as with maize. Possibly this was because of the competition from the grasses, which performed best in the turnip site in summer and autumn. Interestingly, while grass production was highest in the grass to grass site during spring, by autumn, there was significantly less grass in this paddock than in the brassica paddock. Pooling data for the diploid grass (Bronsyn 16) versus the tetraploid (Quartet 20) showed that there was significantly less clover in the diploid plots than the tetraploid plots. There was correspondingly more grass in the diploid plots. This is likely to be due to the lower tilling of the tetraploid grass allowing more light to reach the clover at ground level. In summary, the introduction of a break crop and choice of grass type (diploid or tetraploid) can significantly alter the composition and productivity of re-established pasture and could be used to increase clover cover.

A general cost-analysis of the clover re-establishment trial has recently started by AgResearch and is in the early stages. This economic analysis ties together the different trials comprising the project with the aim of costing different CRW management scenarios.

March 2007

The goal of this project is to compare a range of pasture establishment and management regimes in order to develop scientifically-based recommendations of how to best manage pasture in the presence of the weevil. It includes nitrogen fertiliser strategies that will give affected farmers a breathing space until longer term controls, such as biological controls and tolerant clover cultivars, become widely available.

Field trials investigating pasture establishment, use of N fertilizer and different pasture management options are in progress on North Island clover root weevil-infested farms. These N fertiliser trials (Milestone 2.3) are aimed at identifying best practice for the application of N fertiliser for clover growth in weevil-infested pastures. Two trial sites (Holmes vs. Wilson sites) have had fertiliser treatments and measurements of production/composition taken at each grazing since November 2005. Prior to July 2006, no significant differences were evident between treatments in the fertiliser plot trials for either fertiliser rate (0, 100, 200 and 400 units N) or grazing regime (conventional vs. optimal). As reported in October 2006, this may have arisen from the combination of good growing conditions and the possibility that soil fertility was moderately high at commencement of the trials.

Throughout spring and summer, clover cover at Wilson’s tended to be highest in plots under the optimal pasture grazing regime, although statistically significant differences between optimal or conventional pasture heights was only observed in October. No such trend was found at Holmes’. No interaction was found between cutting height and N application on pasture cover. It was seen that at Wilson’s from winter, through spring and into early summer, application of 400kg/ha/yr nitrogen fertiliser gave a significant increase in productivity compared with no fertiliser treatment. Application rates of 100 and 200 kg/ha/yr offered no significant increase in productivity over applying zero nitrogen. Furthermore, during winter and spring only, but not summer, 400 kg/ha/yr nitrogen fertiliser gave significantly increased pasture productivity compared to 100 kg/ha/yr. Neither cutting height nor nitrogen application rate had any influence on pasture productivity at Holmes’.

These results may reflect differences in farm management at the two sample sites; Wilson’s farm uses a low-input, high output regime whereas Holmes’ farm is more intensive and practices a high input, high output approach. It may be that modifications relating to nitrogen application and grazing height had no effect on the land at Holmes’ because it was already so intensively treated that it was unable to respond to further interventions.

The single replicated clover re-establishment trial (Milestone 3.1) in the Waikato is aimed at comparing the role of cropping on subsequent clover establishment and production. It was commenced in April 2004 on the property of R. Henderson, Horsham Downs. While considerable data has been collected, the timing of the collection of pasture production data relative to grazing has changed during the course of the trials. However, data collected since the timing was changed suggest that there are differences in clover re-establishment in the presence of diploid (Bronsyn) and tetraploid (Quartet) grasses depending both on pasture renewal options and also sowing rate in Spring 06. It appears that following a forage crop results in significantly higher levels of clover in pastures, and that the use of a lower tilling grass (Quartet) can promote higher levels of clover than diploid ryegrass at similar total pasture production levels.

Quarterly Update: October 2006

The key focus of the project in this quarter has been on-going trial site data collection for Milestones 2.3 and 3.1. These trials are comparing a range of nitrogen fertiliser application rates on pasture and clover production/vigour/sustainability (Milestone 2.3) and examining Clover Root Weevil (CRW) re-establishment in CRW infested areas under a range of pasture renewal options (Milestone 3/1).

Nitrogen Fertiliser Trials

Two plot trial sites (Keith Holmes, Tauhei - peat soil; David Wilson, Hoe O Tainui, mineral soil), have had fertiliser treatments and measurements of production/composition taken at each grazing since November 2005. With regard to field days, CRW impact is most visually evident in late spring-early summer. However, given the lack of differences between treatments in the first six months, an autumn field day may provide data of more interest to farmers

Two paddock evaluations are underway, in Northland and the Bay of Plenty. Taranaki, Hawke’s Bay and Manuwatu site assessments and paddock evaluations are progressing.

Clover Re-establishment in CRW Infested Areas

These trials commenced in April 2004 on the Horsham Downs property. While considerable data has been collected, the timing of the collection of pasture production data relative to grazing has changed during the course of the trials. The team needs to ensure the data from the old and new data sets relate correctly to each other, and thus wish to obtain a few months more comparative data before trial results are released to public scrutiny.

The recent project Governance Group meeting (6 October 2006) provided an opportunity to discuss related AgResearch initiatives on CRW biocontrol agents. The spread of CRW into South Island locations and responses to this were considered. The Clover Root Weevil Action Group identified the need for improved national coordination and integration of CRW research and management initiatives.

June 2006

Current knowledge (published and unpublished) on clover root weevil (CRW), both in the science and farming community, has being compiled. Farmer observation was important and anecdotal information from farmers was collected by researchers and consultants from diverse CRW affected areas in the North Island through interview and questionnaire. The focus was on measures taken by farmers to combat white clover decline in their pastures. An initial draft report that collated information on the impact and life cycle of CRW has now been peer reviewed by farmers in the project’s Governance Group and published by AgResearch. The report is entitled “Managing clover in the presence of Clover Root Weevil: A summary of current knowledge prepared for New Zealand farmers”.

The project involves upskilling farmers to better manage clover in their pasture to mitigate the effects of CRW. The farmers (regional champions) to be upskilled have been identified and the regions they represent are Northland, Waikato, Taranaki, Manawatu and Hawkes Bay. These farmers are also members of the New Zealand Clover Root Weevil Action Group and Governance Group members of this SFF project. Upskilling this national group of farmers has involved introducing them to Waikato farmers who have long experience with clover root weevil and who have been experimenting with mitigation strategies on their own account. There have been three meetings of the project’s Governance Group in Year 1 of the project, including farm site visits in the Waikato.

Another key focus of the project in this quarter has been on-going trial site data collection for Milestones 2/3 and 3/1. These trials are (1) comparing a range of N fertiliser application rates on pasture and clover production/vigour/sustainability (Milestone 2/3) and (2) examining CRW re-establishment in CRW infested areas under a range of pasture renewal options (Milestone 3/1).

March 2006

Current knowledge (published and unpublished) on clover root weevil (CRW) both in the science and farming community, has being compiled (Milestone 1/1). Farmer observation was important, and anecdotal information from farmers was collected by researchers and consultants from diverse CRW affected areas in the North Island through interview and questionnaire. The focus was on measures taken by farmers to combat white clover decline in their pastures. An initial report has now been drafted that collates information on the impact and life cycle of Clover Root Weevil (CRW). This report is now been peer reviewed by farmers in the project’s Governance Group prior to being finalized.

A key component of the project involves upskilling farmers to better manage clover in their pasture to mitigate the effects of CRW. The farmers (regional champions) to be upskilled have been identified and the regions they represent are Northland, Waikato, Taranaki, Manawatu and Hawkes Bay. The upskilling process has been started by introducing them to Waikato farmers who have long experience with clover root weevil and who have been experimenting with mitigation strategies on their own account. The upskilling process (Milestone 1/2 will be completed when Milestone 1/1 (the CRW information review) is achieved and the report can be discussed with the regional champions. This Milestone is likely to be completed by the end of the fourth quarter of the project (30 June 2006).

The identification of trial sites and collaborating farmers and establishing background information on sites (Milestone 2/1) has been completed. The focus this quarter has been on trial site data collection (Milestones 2/2 and 3/1). Base line data has been collected. This forms an essential platform from which to measure the composition and production changes induced by the treatments. No changes are as yet measurable, or expected.

December 2005

Current knowledge (published and unpublished) on clover root weevil (CRW) both in the science and farming community, is being compiled. Farmer observation is also important, and anecdotal information from farmers will be collected by researchers and consultants from diverse CRW affected areas in the North Island through interview and questionnaire. The focus will be on measures taken by farmers to combat white clover decline in their pastures. An initial report has now been partially drafted that collates information on the impact and life cycle of Clover Root Weevil (CRW).

A key component of the project involves upskilling farmers to better manage clover in their pasture to mitigate the effects of CRW. The farmers (regional champions) to be upskilled have been identified and the regions they represent are Northland, Waikato, Taranaki, Manawatu and Hawkes Bay. The upskilling process has been started by introducing them to Waikato farmers who have long experience with clover root weevil and who have been experimenting with mitigation strategies on their own account. These regional champions are also members of the project’s Governance Group. The primary role of this group is to monitor implementation and delivery of the project.

A significant gap in the CRW management information set is knowledge on strategic use of nitrogen fertiliser to maintain clover growth and persistence in the presence of CRW. Small plot trials will be established in the Waikato to compare a range (minimum 4) of low rates of N fertiliser on pasture and clover production/vigour/sustainability. These will provide data to modify fertiliser models currently used by fertiliser companies to provide fertiliser advice. The background data required for the trials planned under this objective have been collected. Three sites were selected based on initial clover and clover root weevil population densities and differences in soil type. All three trials are located in the Waikato and represent an organic soil, a mineral soil and a heavy clay soil. The treatment regimes at each trial site have now been established and data collection has commenced.

The presence of CRW adult populations in autumn renovated pastures poses a major problem for clover re-establishment. Adult CRW preferentially feed on clover seedlings reducing clover re-establishment to nil in many cases. An option to improve clover establishment is to grow a summer crop that is not a CRW host to eliminate the CRW population. In 2004 six trials (3 Waikato 3 Northland) were established to enable three pasture renewal options to be compared. Ryegrass/white clover pasture was sown following either 1.maize 2. turnips or 3. pasture to pasture. We propose to continue these measurements for a further 3 years at the Waikato site to assess the costs of establishment against the longer term benefits and track CRW/nematode re-infestation. Data collection at the Waikato trial is continuing under this project objective.