The Canadian government plans to phase out most uses of two pesticides linked to the deaths of bees and other insects, a move environmental groups say is welcome but should be implemented immediately.

Health Canada said on Wednesday it will ban most outdoor uses of clothianidin and thiamethoxam over three to five years because “harmful levels” of the chemicals in rivers and streams are also affecting mayflies, midges and other aquatic insects, an important food source for fish and birds.

Scott Kirby, director-general of Health Canada’s Pest Management Regulatory Agency (PMRA), said the phase-out will begin after a consultation period next year. He said most uses of the chemicals will end within the three-year period but added that the longer time frame is needed so growers can find replacements.

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Environmental groups and critics of the PMRA called it a significant step in the effort to protect bees and other pollinators, but said the ban should be in place sooner.

Ottawa previously announced a phase-out of a related product, imidacloprid, and all three pesticides facing a ban are in a class known as neonicotinoids, widely used to grow canola, soybeans and other field crops as well as sod, ornamental flowers and vegetables.

The insecticides are systemic, which means they become part of the plant and render it toxic to bees and other insects. Studies have shown the neurotoxins affect bees’ ability to find food and maintain healthy, productive colonies. The products are slow to break down in the soil and can wash into water bodies.

Tibor Szabo, who raises and sells queen bees in Guelph, Ont., and sits on the board of the Ontario Beekeepers’ Association, said the proposed ban comes too late for beekeepers who have lost hives and struggled to stay in business.

“These things should never have been conditionally registered without any risk assessments done on bees,” he said. “That was a complete rip-off of the taxpayer. It killed so many pollinators in the past 10 years that there is no way they will ever be replaced – the genetic diversity that has been lost is permanent.”

He said chemical companies are constantly developing and marketing new systemic pesticides that are just as lethal to insects as the ones being banned, touching off years of testing processes in which bees and other pollinators are threatened.

“If they pull these ones, what the hell are they doing about all the other ones that have popped out on the market in the past few years?” he said.

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Health Canada’s Mr. Kirby dismissed concerns the pesticides would be replaced by equally harmful substitutes. “Any registered pesticide is considered acceptable for use until we undertake … a re-evaluation every 15 years or until we have information that would lead us to initiate a special review for reasons of risk,” he said.

His agency faced criticism on Wednesday for its past practice of allowing pesticides to be used before fully examining the risks. The policy, known as conditional registration, was ended in 2016 but permitted the widespread use of thiamethoxam and clothianidin.

“Canada’s ‘approve now, study later’ approach has used our environment as a guinea pig. It is now clear by scientific consensus that [neonicotinoids] pose significant harm to ecosystems,” said Karen Ross of Montreal-based environmental group Equiterre. “By not acting quickly, the PMRA continues to fail in its mandate to protect Canadians and the environment.”

Health Canada said it will ban the use of clothianidin for outdoor farming and turf uses and the use of thiamethoxam for outdoor farming and ornamental plants. Greenhouse growers will be excluded. The proposals will be subject to a 90-day consultation period before a final decision is made at the end of 2019.

Spokespeople for Syngenta Canada, Bayer Canada and Sumitomo Chemical, makers of thiamethoxam and clothianidin, were not available to comment. But Syngenta said in an e-mail that it is “disappointed” and believes Ottawa did not consider additional information.

“Given the challenges of farming, taking tools away is a serious matter,” pesticide lobby group CropLife Canada said in a statement. ”This is especially disappointing and confusing to many given that earlier this year the PMRA released a seemingly contradictory proposed decision validating the safety of both of these products to pollinators as seed treatments, which is one of their primary uses.”

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In a statement, the Grain Growers of Canada said it is reviewing Ottawa’s decision and worries the government is acting too quickly to take farmers' concerns into account.

The three most popular neonicotinoids are banned in Europe and used under tight regulation on soybeans and corn in Ontario.

Beatrice Olivastri, the chief executive officer of Friends of the Earth Canada, one of the groups that have led the fight against the use of the pesticides, noted that Ottawa’s move comes shortly after the United States lifted a ban on neonicotinoids and genetically modified crops in wildlife refuges where agriculture is allowed. “Here’s Canada taking a positive step in the face of the U.S. going backward,” she said by phone.