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Spray options open up for farmers

Words by Richard Rennie


In a social media ‘news’ environment where fiction can quickly be taken up as fact, consumers wanting to understand where their food comes from and how safe it is, can struggle to know if what they are hearing is real, or indeed true.

Opposition to pesticides and herbicides is also bringing pressure to bear on farmers charged with growing high quality food in a way that is sustainable for the planet, and economic for them.

The most virulent debate lately around the use of sprays on crops has been the use of glyphosate. The low residue spray is one of most frequently used herbicides whose development 40 years ago helped revolutionise agriculture and redefine sustainability in both cropping methods, and spray practices.

The debate around glyphosate was ignited back in 2015 thanks largely to a classification of it as a “carcinogen” or cancer causing agent by the International Cancer Research agency.

What was often not reported was the same announcement also included some common everyday products and foods including talcum powder, coffee and bacon as “possibly carcinogenic”.

At its simplest level, almost anything will cause cancer if ingested in sufficient volumes.

Agcarm is the group representing chemical companies supplying New Zealand with crop and animal treatments.

Chief executive of Agcarm Mark Ross said this classification has caused a huge degree of unnecessary concern among the public, given this was the only World Health Organisation agency to find a link between glyphosate and cancer.

“The IARC review was not a risk assessment. The actual risk is determined by the type and extent of human exposure,” he said.

“This was reinforced by the United Nations’ Food and Agriculture Organisation (FAO) group stating glyphosate was unlikely to pose a carcinogenic risk to humans from exposure through the diet.”

New Zealand’s own environmental watchdog, the Environmental Protection Agency has also concluded the product was unlikely to be carcinogenic.

The swirl of debate around glyphosate highlights how vulnerable consumer perceptions are to interpretation of data. Mark Ross points to the 800-plus studies which have all validated the product’s safety.

Meantime debate has also been constantly lapping at the use of another family of sprays used in insecticide control – neonicotinoids.

Used to protect crops often in seed treatment form, there has long been debate the residual impact from the seed treatment has been to have a systemic effect on plants, lasting the plant’s lifetime and therefore having an impact upon bees pollinating that mature plant. 

The collapse of bee populations in Europe has been blamed upon “neo-nics” and similar claims in localised districts have also been made here in New Zealand in the past decade.

But both Australia and New Zealand have had 25 years of neonicotinoid use and bee populations in both countries are at all-time highs.

The depletion of bee populations in some areas in the past decade at different times has been instead attributed to the varroa mite establishing here in the early 2000s, to the extent bees now rely upon human intervention to keep them healthy.

An Agcarm report on the economic value of seed treatments using neonicotinoids to the New Zealand economy indicated if they were removed it would cost the economy between $800 million and $1.2 billion in the short to medium term.

In an effort to try and fill the control gap left in their absence, farmers would be forced to blanket spray emerging crops, at significantly greater cost and higher levels of pesticide use per hectare.

A small survey of registered dietitians in the United States late last year found over 90% of them were concerned fear based messaging about pesticides on produce was causing unnecessary concern over whether conventionally grown fruits and vegetables were safe to eat, in turn having a significant effect upon healthy dietary intakes.

New Zealanders’ fruit and vegetables are constantly monitored through the New Zealand Total Diet Study, giving consumers the highest level of assurance their food is safe.

The latest study issued in May 2018 confirmed pesticide chemical residues found in New Zealand foods are at levels far below tolerances established by national and international food safety standards, and do not pose a safety concern.

In fact, the amount of pesticides found were actually lower today than in the past and consumers should not feel compelled to “go organic” simply to avoid residues in conventional crops.

But with perception often forming 90% of reality, more farmers are recognising the value in seeking options to chemical treatments if possible. This is as much to avoid resistance developing in weeds and pests than for any perceived residue risk.

Regenerative agriculture is proving to play a part here as more farmers look to ways to minimise tilling their soil, build organic matter up and increase their farm’s biodiversity.

With that comes the added benefit of lower fertiliser and crop treatment costs.

Canterbury farmer and Ruralco member Simon Osborne has become a face for the practice in the South Island after he continued the radical “no till” approach adopted by his father in the 1970s.

Years of tillage had left the farm’s soil tired and depleted when his Dad decided to go that way, quite a shift in mindset for farmers at the time.

Over time and now under Simon’s guidance, the farm has had a gradual improvement in soil quality with organic matter doubling from what it was in the 1970s. 

Practices include re-incorporating stubble into the soil, and growing cover crops with up to 20 different species of plants all mixed together.

He is also experimenting with inter-crop plantings combining the likes of crimson clover with cereals – these have helped suppress weed growth, and with that comes a need to use less herbicides.

Further work in combining crop types may lead to even greater reduction in chemical control use, with some crops forming natural pyrethrums to repel pests from the main crops being grown.

For Simon, the practice is very much a series of experiments which has also included re-thinking what constitutes a “tidy” farm.

Instead, fence lines as living strips to grow plants along that may play a role in building soil carbon and providing a place for organisms and insects to overwinter in.

Biological controls for pests and diseases on farms is often associated with bringing in a predator pest to deal to a problem pest.

Often seen as a living “ambulance at the bottom of the cliff”, New Zealand has enjoyed some good successes with this non-chemical approach in the past.

The most recent has been AgResearch’s introduction of the parasitic wasp M.aethiopoides to control the clover root weevil that devastated New Zealand’s invaluable clover reserves on farms from Northland to Canterbury in the early 2000s.

Losses of 50-100% of pasture clover were recorded on farms, pushing farmers to have to reach for synthetic nitrogen to make up the shortfall, with the inevitable environmental impacts that brings.

New Zealand also now has the Samurai wasp on standby and already approved as a biological control agent should this country be overrun by the dreaded Brown Marmorated Stink Bug.

Already rife throughout fruit growing areas of northern Italy, the stink bug has a voracious appetite and has written off that country’s pear industry and is costing the sector almost NZ$400 million a year in lost earnings.

Should it get into New Zealand, the losses would mount quickly as it ate its way through most of the country’s significant horticultural crops before establishing in seed and cereal areas.

The work by New Zealand researchers with their Italian colleagues on stink bug control is also developing some non-chemical techniques that may yet provide solutions to controlling other bugs. 

Professor Max Suckling, New Zealand’s leading authority on biological control, is excited by a range of methods rapidly being developed in conjunction with the Italians.

One of these is biotremology technology which involves using synthesised insect mating calls to draw pests from across an orchard area into a trap.

It is a type of “pied piper” technology in its infancy that may prove effective in fighting stink bugs in Italy, and being a monitoring tool in the early stages of an outbreak here in New Zealand.

Professor Suckling and his team in New Zealand also earned international recognition for their work with sterile moths to control a codling moth outbreak in Hawke’s Bay orchards in 2018.

A million sterile moths were imported in 2018 and dropped by drone over orchards to breed with the local population, dramatically reducing the moth population without any use of additional insecticide.

Pheromone traps were used to draw in and monitor the results, with just one adult codling moth captured in a 100ha orchard after the drone ‘attack’.

It is a technique Suckling believes could be applied to the stink bugs, should they advance into New Zealand orchards and farms.

Reducing insects and disease using fungal endophytes is another novel non-chemical approach to dealing with pests and diseases in crops that New Zealand researchers are leading the world in.

Living naturally on plants, endophytes have already been used with great success as the AR1 and AR37 endophytes. AR37 is the only endophyte to offer protection against porina caterpillar and Argentine Stem weevil larvae, while AR1 offers protection from Argentine Stem weevil adult and the mealy bug.

Funding to AgResearch is helping scientists look harder at endophytes in cereal crops, isolating those that may have a positive benefit for crops, and inoculate them into other cereal crops.

Trial crops at Lincoln are studying potential gains in crop productivity or pest control.

Early indications are the main role will be in being “bio-controls” for pests, similar to what AR37 does.

The researchers are also revisiting ancient maize varieties from Mexico to see if they can identify any endophytes that may have been lost due to commercial varieties coming to dominate the seed market.

About the Author


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