Bioagent does its job against clover root weevil but black beetles still a problem

Clover is the base plant of New Zealands pastoral plant mix, providing  nitrogen to fuel the accompanying grasses, and quality high energy feed from its foliage.

The outbreak of clover root weevil in 2006 in the north and south, was a major blow to maintaining a low cost system which has been basis of  pastoral farming here for many years. However the team at AgResearch identified a biological control agent in a parasitic wasp that attacks the weevil and limits its spread, and it appears from this article it has already been very successful.

Black beetle damage is increasing again, and a new campaign aimed at gaining a greater understanding of the pest, and developing an early warning system has been launched. The early failure of newly established pasture is a major concern and research into black beetles damaging role into these new pastures should yield a good return for the research dollars invested.

The introduction of a biocontrol agent for clover root weevil in 2006 has done much to suppress the pest’s impacts, but vigilance is still critical to detect new infestations and ensure that the biocontrol agent quickly reaches the areas where it is needed. When clover root weevil (CRW) was first found in 1996 in Waikato, almost nothing was known about its impact on pasture or about how to manage it.

In 2006, AgResearch scientists, supported by DairyNZ, Beef + Lamb NZ and AGMARDT, made a breakthrough in CRW control by releasing a potential biocontrol agent, a tiny parasitic wasp from Ireland. The first trial releases were made in Waikato, Hawke’s Bay and Manawatu, and within just 18 months the wasps’ performance had exceeded the expectations of even the most optimistic scientists. Although the biocontrol agent can never entirely eliminate CRW, it can strongly suppress the pest within just a year or two of arriving in a new area, alleviating some of the pressure both on pastures and on farmers’ pockets.

AgResearch distributed the biocontrol agent throughout the North Island as quickly and comprehensively as possible, in part by giving it away through industry networks and at field days so farmers could make releases on their own properties.  CRW is now in decline at all sites AgResearch has monitored and only in the Far North are there concerns that the weevil could still retain the upper hand.

Meanwhile, on the South Island CRW made its first unwelcome appearance near Christchurch and Nelson in 2006. Fortunately for South Island farmers, the biocontrol agent for CRW, which had just been liberated in the North Island, was available for immediate release in southern pastures. AgResearch quickly introduced the biocontrol agent to large populations of the weevil at Richmond and the Rai Valley in 2006, and then again in Golden Bay in 2009 in the hope that the wasps would spread along with CRW and thereby minimise the pest’s damage in the South Island.

Again, the biocontrol agent exceeded expectations by catching up with the outer limits of CRW populations in Golden Bay, Nelson and Marlborough, and then staying hot on CRW’s heels as it expanded southwards. Sampling in 2011 showed that the wasp has been carried by the weevil south as far as Springs Junction and Kaikoura. It has also reached Lincoln, probably from North Canterbury or Rakaia Island where it had previously been released.

Experience shows CRW is very difficult to detect during the first few years of its arrival at a new location, partly because it is initially present in very low numbers and also because it spends much of its time hidden underground as a larva or pupa. The build up of CRW in a new location is insidious, and sometimes farmers only realise the pest is present once their clover has all but disappeared. Notching of white clover leaves and feeding damage on root nodules are symptoms of CRW, but careful observation is required to detect these symptoms before the pest has reached high numbers.

This means AgResearch’s CRW monitoring is imperfect and some infestations could remain undetected for years unless farmers assist by being vigilant and reporting their observations. Advising AgResearch that CRW is suspected in a new location will help scientists to ensure the biocontrol agent quickly reaches the areas where it is needed.

And the other pasture pest, black beetle is being attacked with substantial research funding to try and beat its damage to young pastures in the central north island.

A Waikato research group has been awarded almost $500,000 in funding to "beat the black beetle" and going a long way to developing pest-resistant dairy pastures in the region reports The Waikato Times.The Waikato Black Beetle Action Group, in conjunction with AgResearch, has been awarded the three-year MAF Sustainable Farming Fund grant, that will be matched by a similar level of cash and in-kind contributions from DairyNZ, seed companies, industry and farmers.

AgResearch farm systems team leader Warren King said the impact of black beetle on pasture production in the Waikato and throughout the northern North Island was significant."Farmers in these regions are experiencing widespread failure of perennial pastures, many of them within 12-24 months of successful establishment," he said.A recent survey of more than 700 Waikato and Bay of Plenty dairy farmers highlighted that pasture failure was the single biggest problem on-farm and black beetle was widely identified as one of the major culprits.

"This project will contribute to the development of a communication programme to inform Waikato farmers and the wider industry of the factors that result in damaging black beetle populations and how to minimise future pasture losses," Dr King said.Research will include on-farm trials where pasture production and composition would be monitored, along with persistence through time, pest insect populations and endophyte infection rates.

Dr King said the team would also work towards developing a warning system to initiate farmer decision-making. He said predictive models for black beetle outbreaks were developed in the 1980s, but changes in both pasture composition and climate meant they were no longer valid.