Around the globe, glyphosate is the most widely used herbicide. That is also true for New Zealand, where the weedkiller is used in about 90 products. The most recognised brand is Roundup.
It is an effective herbicide, killing hundreds of different weeds and grasses, roots and all.
Where windblown glyphosate spray reaches other plants it can cause fasciation, a mutation of the plant, New Zealand entomologist Anthony Harris says.
"The cause of fasciation can be genetic, bacterial, fungal, viral, physical or environmental," Harris, Otago Museum’s honorary curator, says.
"Fasciation is the name given to the abnormal growth in plants when a usually cylindrical part of the plant ... becomes flattened to become a ribbon-like structure."
When it comes to the effect of glyphosate on humans, the jury is still out but the argument is in full swing.
In 2015, the United Nation’s International Agency for Research on Cancer said glyphosate was a probable carcinogen for humans.
Four years later, a United States court found that Roundup probably causes cancer. It also found that pharmaceutical and chemical giant Bayer — one of the biggest producers of glyphosate-based products — had acted maliciously in hiding this fact.
The next year, however, the United States’ Environmental Protection Agency said glyphosate did not pose a risk to humans as long as it was used according to directions.
Bayer continues to "stand strongly" behind its product. It has also announced it will no longer sell glyphosate-based products in the US residential lawn and garden market from some time next year.
In New Zealand, the Ministry of Primary Industries says since 2014 it has run several tests for glyphosate residue in food. It detected no residues in milk or cream or in pea crops. Its conclusion about wheat crops and honey was "no health or food safety concern detected with present glyphosate levels".
Europe is now the main glyphosate battleground.
The European Union’s authorisation of glyphosate runs out in December. But based on recommendations by Bayer the EU decided to renew it.
However, cancer researchers are challenging that, saying 33 of 35 studies the Bayer analysis was based on were incomplete.
A final decision by EU countries on glyphosate will be taken this year.
