An expert on pesticides said more research is needed to determine the impacts they are having on mental health.
Last year, after a two-year investigation the Environmental Protection Authority (EPA) banned a number of commonly used pesticides and introduced stronger controls for many others.
It said that while the group of pesticides, mostly organophosphates, play a crucial role in protecting plants from insects, they also pose a major threat to human health.
The EPA also banned them from residential use - saying it was likely many home gardeners do not appreciate the acute health risks organophosphates pose - particularly to pregnant women and children.
Massey University professor Jeroen Doues has just received more than $1 million of government funding to investigate the impacts of pesticides on children.
He believes more research needs to be done on what impact long-term low-level exposure to organophosphate and carbamate pesticides have on mental health.
In New Zealand, in common with the rest of the developed world, depression and suicide rates in rural areas far outstrip those in urban areas.
Male suicide rates in rural New Zealand are 67 per cent higher than in urban areas.
Professor Doues said pesticides are designed to interrupt neurological processes.
"Pesticides are designed as neuro-toxins so they're very effective in killing bugs.
"But unfortunately, because they're designed to affect the neurological networks in insects they also have an effect on neurological networks in humans," he said.
Professor Doues said while it's known that exposure to high levels of organophosphates and carbamates can lead to suicidal thoughts and depression - what's not so well known is the impact of chronic low-level exposure - such as what happens on farms.
He said its crucial farmers are very careful when they use pesticides.
"Guidelines need to be followed, pesticides need to be locked up so that kids don't have access to them. Then I think when pesticide spraying takes place people will have to make sure to use appropriate protective equipment and ensure that the other family members are protected."
It was important farmers followed the spraying instructions on the label of pesticides, Prof Doues said.
Other factors could also contribute to the higher suicide rate among farmers, such as access to poisons, firearms and the inherent financial uncertainties of farming, he said.
"There is, in fact, quite a bit of evidence these days that pesticide exposures are associated with anxiety and depression, suicide, suicide attempts, thoughts about suicide but we also know that pesticides may have an affect on cognitive function, dementia," Prof Doues said.
"In children we know it's associated with developmental disorders, delays in cognitive development, attention deficits, behavioural problems.