Researchers put $1.4bn price tag on insect damage to NZ dairy economy

This lack of awareness has spurred scientists at AgResearch to investigate the harm caused by invertebrate pests such as the grass grub, black beetle and various weevil, in terms of lost productivity for pastoral farming.

“That was the main prompt, although as entomologists we are aware that pasture pests have been causing our farmers a lot of trouble. But it has been very difficult convincing funding providers and even the farmers themselves that doing something about this damage is worthwhile​,” said Colin Ferguson, a researcher national agriculture research institute.

To get farmers in particular to understand that these pests are worth trying to combat, Ferguson and his colleagues sought a means to convince them.

The researchers decided the best way to do so was to put a dollar value on the scale of damage that the insects have been causing, or the cost in terms of lost production that they are responsible for. 

Using this approach, they secured funding from organizations such as DairyNZ, Dairy Companies Association of New Zealand and Fonterra, as well as various beef and governmental bodies.

Their study, “Quantifying the economic cost of invertebrate pests to New Zealand’s pastoral industry,​” was published last month in the New Zealand Journal of Agricultural Research. ​

Financial cost

In it, the team place a nationwide cost of up to NZ$2.3bn (US$1.5bn) to pastoral-based production from the pests in an average year, from which they estimate NZ$1.4bn is lost to dairy farms.

“We mined a lot of research that the authors and others had done over the last 20 or 30 years to come up with some what we hope are reasonably robust figures,​” said Ferguson.

“Our research shows that the impact of the grass grub alone costs dairy farms up to NZ$380m each year​. It’s certainly [more accurate] than the other estimates that we have got so far.​”

Range of pests

Farmers generally agree the grass grub is the most serious insect pest. It causes damage when its larvae feed on plant roots, which create yellowing patches in the paddock. These develop into areas of dead plants as the larvae numbers build up.

Another pest, the clover root weevil, can reduce the amount of nitrogen provided by clover, which is also a high-quality food for livestock, as part of the food chain.

North Island dairy farmers have reported substantial loss of productivity due to the weevil, with reductions in nitrogen fixation by clover of 50-100%. To compensate for this damage, farmers must then buy quantities of nitrogen fertilizer.

Losses attributable to pasture pests have traditionally been determined either on the basis of the amount of foliage they consume, or reduced pasture production.

AgResearch’s study, though, has used reductions in pasture production to estimate the impact on milk production revenue for dairy farms, as well as on meat production revenue for sheep and beef farms.

This approach, the report says, provides a good picture of the financial challenges farmers face with pasture pests, and reinforces the need to invest in new and cost-effective ways to better control them.

Pest control

To do so, AgResearch has been looking at pest control on a number of fronts, including the development of new bio-pesticides—naturally occurring organisms that can be used to target specific pest species, rather than chemical treatments that can be expensive and have unwanted impacts on the environment.

Scientists say this research has been progressing quite well and giving good results, though New Zealand’s remote location means it faces trouble from at least two major pests that are endemic to its islands—meaning they do not occur elsewhere in the world.

This makes bio-pesticide development to control these insects particularly expensive due to a lack of scale when the time comes to take these bio-pesticides into commercial production.

“There is a real need for bio-pesticides at the moment​,” said Ferguson, who has spent years researching the compounds. ​

“A lot of our farmers rely on organophosphate insecticides, and there’s a lot of pressure from regulators, consumers and farmers themselves to decrease if not eliminate their use, leaving quite a void in the market. ​

“Biopesticides will fill that void—it’s just a matter of getting them to the stage where they can be used easily at an affordable price​.”

Hard to quantify

So why have farmers been slow on the uptake to address pasture pests, as Ferguson suggests, when they are paying for the destruction they cause?

David Burger, strategy and investment leader at DairyNZ, which represents dairy farmers, says it has been difficult to assess the scale of the harm caused by pasture pests at farm level, though measures have been taken to address their damage.

“Dairy farmers know invertebrate pests mean less grass for animals, and pastures require renewal more often, costing them time and money. Pasture pests also make pastures less resilient and open to other impacts​,” he said.

“Most dairy farmers are aware of the specific pasture pests which affect their region and will buy treated seeds to manage them. Unfortunately the overall impact from pasture pests is difficult to quantify at farm level​.”

DairyNZ has been investing on the behalf of dairy farmers in biological control agents, and research to identify more resistant varieties of plantain and clovers.

For instance, it has sponsored work by AgResearch into introducing a biocontrol agent for clover root weevil in the form of a small parasitic wasp. This injects an egg into adult weevils to render them unproductive, and has shown success.

Now the wasp is present in most areas of North and South Island, and has reduced weevil populations by around 90% in some areas, further research into the population dynamics of biocontrol agents for the clover root and Argentine stem weevils will ultimately maintain or improve their effectiveness.

“Trials are also underway into black beetle and whether naturally occurring fungi could be used as a biocide, along with identifying the right soil pH for farmers to produce clovers, while balancing suppression of black beetle​,” Burger added.

Financial gain

Back at AgResearch, Ferguson believes farmers have enough to contend with before looking for new problems to fix, such as the control of pasture pests, though any time and investment they make to this end is bound to be worthwhile.

“Generally farmers have 101 things on their plate every day, and they don’t tend to think ahead about insect damage and try to predict when it’s going to happen​,” he said.

"It’s not until it actually happens that they respond to it. By then, of course, the damage is done, the money has been lost and they can’t get that back, so what we are trying to get them to do is to think about it before it happens and make an informed decision​.”

It may cost NZ$30-40 per hectare to do something about this, he said, but doing so might provide a return of several hundred dollars or even more.

“It should prompt farmers to think a lot more about that and give them an indication of the sizes of the losses they are experiencing, and hopefully increase awareness​,” he added.