Dr Jacqueline Rowarth: In defence of glyphosate

In roadsides across the country, glyphosate is a cost-effective method for controlling weeds. File photo / Stuart Munro

Opinion: Glyphosate herbicide is approved in New Zealand because the positive aspects are indisputable and, when guidelines on use are followed, no link to cancer has been shown, Dr Jacqueline Rowarth writes.

It's difficult to avoid the glyphosate/Roundup controversy.

We have advertisements promoting glyphosate-free and organic weed control. Media cover stories of councils avoiding it and the Environmental Protection Authority (EPA) reviewing it.

In addition, we have articles on the number of people who submitted to the EPA on whether New Zealand should be using it, whether they know anything about it or not.

Note that knowledge requires more than reading social media.

Social media's coverage of glyphosate has been on a par with that for the Covid vaccine – misunderstandings, mistruths and alarmist activist statements purporting to explain the reality.

And the language used is hyperbolic with anti-chemical lobbyists stating, for instance, that New Zealand is "drenched" in the chemical.

It isn't.

International comparisons indicate that New Zealand is a low user of glyphosate.

Part of this is because it is mostly used on cropping land and the area in New Zealand suitable for crops is small. In cropping it is applied between crops to help with the establishment of the next crop by removing weeds.

It enables minimum tillage practices which reduces the use of fossil fuel and maintains organic matter in the topsoil.

In urban environments or roadsides across the country, glyphosate is a cost-effective method for controlling weeds. Because its action is systemic, that is it disrupts a biochemical pathway found in plants (but not in other types of organisms), it kills the plants and further control in an area is not required until more unwanted plants appear.

Mechanical weeding can be effective, but involves more tractor time and hence fuel consumption (and greenhouse gas production), than the use of glyphosate.

Research in Australia comparing thermal weed control (flaming and hot water application), with glyphosate showed that flaming was not successful except on very young weeds.

Two applications 3-4 weeks apart of hot water were equally effective as a single dose of glyphosate.

However, hot water requires special equipment (and water), creates its own health and safety problems, and the repeated control measures increases the time and fuel consumption involved in weed control.

Pelargonic acid (or citric, oxalic or acetic) must be very concentrated to be able to burn vegetation, and concentrated acids require special equipment and full personal protective clothing.

Any of the acids can be effective on young seedlings which have few reserves for regrowth. On older plants, the above-ground parts might be set back for a while, but the lack of systemic activity (no movement to the roots) means that the plants are likely to regrow.

In the UK, glyphosate use reduced council weed control to a quarterly event, whereas alternatives required a monthly programme. Again, fossil fuel use increased, and costs quadrupled.

For anybody concerned about climate change, glyphosate would appear to offer advantages. But in California, there have been high profile court cases over glyphosate users and incidence of non-Hodgkin Lymphoma.

In its controversial report in 2015, the International Agency for Research on Cancer alerted the world to potential carcinogen issues related to glyphosate but stated that evidence of a link to non-Hodgkin Lymphoma was limited.

Dr Andrew Kniss, Professor of Weed Science at the University of Wyoming, has calculated that 97 per cent of people with non-Hodgkin lymphoma have had no exposure to glyphosate.

And although there was a 70-fold increase in glyphosate use from its registration in 1974 to the year 2000, the incidence of non-Hodgkin Lymphoma in America peaked and then declined.

Despite the evidence, the statements of the health dangers continue. In New Zealand, the new focus in the media is the people applying the chemical.

Listen to Jamie Mackay interview Dr Jacqueline Rowarth on The Country below:

Again, research exists, and the results are reassuring.

An American study of 55,000 workers, over 80 per cent of whom had used glyphosate, did not find any significant association with cancer at any site.

This was despite not being able to check whether the 55,000 people followed guidelines for use – there was no effect on human health, whatever the way the glyphosate had been used.

Guidelines cover concentration and conditions such as wind to avoid spray drift and impact on non-target species.

The guidelines, therefore, protect the health of the user as well as the environment.

Glyphosate eliminates plants and therefore removes the food source for soil organisms, insects and birds. This means changes to the food chain in the area where glyphosate is used. But not using it means more area under cropping and bigger effects on the environment.

Glyphosate herbicide is approved in New Zealand because the positive aspects are indisputable and, when guidelines on use are followed, no link to cancer has been shown.

Despite this, there are some ratepayers who would rather have their rates increased than allow the council to use glyphosate.

Dr Jacqueline Rowarth. Photo / Supplied

Similar decisions have been made overseas, but statements about countries banning its use need examination – the ban is usually limited to an urban area or, where it appears to be generic, has exceptions for agriculture.

The exceptions recognise that without glyphosate, yields will decrease significantly and the cost of the product to the consumer will increase.

The big question in New Zealand should be why we are spending time and money on research that has already been done.

- Dr Jacqueline Rowarth, Adjunct Professor Lincoln University, is a farmer-elected director of DairyNZ and Ravensdown. The analysis and conclusions above are her own. jsrowarth@gmail.com