Ontario farmer Sean McGivern grows corn and soybeans with the help of the typical menu of pesticides, herbicides and fertilizers.

The one thing he does not use is neonicotinoids, the class of pesticide linked to widespread declines in populations of pollinators.

Instead, Mr. McGivern relies on the age-old practice of rotating crops, so hungry worms and beetles can’t thrive and spread season after season. But he says too many farmers are trying to use neonics to repeatedly grow the same crop in the same field.

It’s a practice that has grown in popularity in step with the rise of neonics, which have been linked to deaths of bees and other pollinators. The pesticides have also been found in water and tied to the reduced numbers of birds and the insects they eat.

The Ontario government plans to put in place rules to reduce the use of neonics on corn and soybeans 80 per cent by 2017, in a bid to cut overwintering bee deaths to 15 per cent, from the current 58 per cent, by 2020. The federal government, meanwhile, is reassessing its approval of the pesticides, which are under a moratorium in Europe.

The Grain Farmers of Ontario, which is the largest farmers’ lobby group, says the “near ban” will handcuff farmers. The group funded a study with the chemical lobbyists CropLife Canada that said restricting neonics will slash crop revenues by $630-million.

The makers of neonics, which include Germany’s Bayer AG and Switzerland’s Syngenta AG, say the seed treatment is safe if used as directed, and pollinator populations are increasing. They say the treatment, which is applied to the seed and makes the plant toxic to insects, protects the environment by helping farmers grow more on existing farmland. “Neonicotinoid seed treatments have contributed to the adoption of conservation tillage practices and the use of cover crops by farmers,” said Erin O’Hara, a CropLife spokeswoman.

“As the economics of growing corn improve, growing consecutive corn crops in the same field is a very tempting prospect,” Bayer CropScience says of its neonic corn-seed treatment, Poncho.

Scientists say neonics impair bees’ abilities to forage, and worsen the effects of viruses and blood-sucking mites. A study from the U.S. Environmental Protection Agency found the chemicals did not boost crop yields. A recent study from Pennsylvania State University said use of neonics actually reduced crops yields by killing the insects that eat plant-destroying slugs.

The seed treatments, which became popular in the past decade, have become an insurance policy for farmers trying to protect their yields. In Ontario, they are used on almost all corn and canola and most soybean seeds, in addition to greenhouse vegetables and flowers.

For Mr. McGivern, whose family has grown grains and raised cattle near Owen Sound, Ont., for 27 years, relying on neonics is akin to treating a person’s high blood pressure without tackling their weight problem.

“Rather than changing up the model to alleviate these pressures, they’re treating the side-effects of a broken system. There are a lot of farmers out there who get it, but there are a lot of farmers who get all their advice from the multinationals that are selling them all the products,” said Mr. McGivern, who heads a group called Practical Farmers of Ontario, which bills itself as a voice for family farms.