Ontario's proposed ban on the sale and cosmetic use of pesticides will be the toughest in North America once it becomes law, supporters said Tuesday.

The legislation promises to take effect faster and go further than Quebec's ban.

Experts warn pesticides could have devastating health effects on vulnerable groups like pregnant women and children, said Gideon Forman of the Canadian Association of Physicians for the Environment.

"The number of products that are going to be banned for use is far bigger than the Quebec list," Forman said.

"Quebec was phased in over three years. This is coming in much, much faster. So it's a huge improvement over Quebec, actually."

More than 300 pesticide products will be banned for use in Ontario once the ban is fully implemented in 2009, Forman said.

His group and several others, including the Canadian Cancer Society and the David Suzuki Foundation, banded together to lobby for a ban, which Premier Dalton McGuinty pledged to enact during last fall's election campaign.

Ontario's ban will likely take effect next spring, but there will be a few exceptions, McGuinty said. Pesticides will still be allowed for use in farming, forestry or health and safety, such as controlling mosquitoes that can carry diseases like the West Nile virus.

Golf courses will also be able to use pesticides, but must meet certain conditions to minimize the effects on the environment.

"What we want to do today is recognize a right that you and I enjoyed when we were growing up, which of late has not been formally recognized," McGuinty said from the backyard of a private Toronto home, as young children wearing "Say No to Pesticides" T-shirts played nearby.

"It's the right of kids to play in the grass, to roll around in the grass and to learn how to do somersaults on the grass without compromising their health."

'Very serious situation'

One of the major concerns with pesticides and young children is leukemia, Forman said.

"There's a lot of research that shows children who are exposed to pesticides are at greater risk for leukemia, which is a very serious situation, to put it mildly," he said.

The provincewide ban is aimed at replacing a patchwork of local pesticide bylaws, but McGuinty said municipalities will be able to introduce tougher rules if they choose.

Many of the details of the ban, such as the penalties for using pesticides, have yet to be worked out, which has become a source of frustration for the opposition parties.

It's "somewhat disconcerting" that so much is being left to regulations, said NDP critic Peter Tabuns.

"At this point, it's still hard to say concretely what's going to be there."

The proposed ban also sets a "very bad precedent" for government policy because it puts a danger label on products that Health Canada has already deemed safe, said Peter MacLeod, a spokesman for CropLife Canada, a pesticide industry association.

"We think this will impact people's perception about food safety," he said. "We think this will impact people's perception about the safety of our medical supply.

"I mean, you're questioning Health Canada."

Some pesticide products are "packaged" in Ontario from active ingredients that are made in the United States, Europe and Asia, MacLeod said.

But lawns and gardens represent only about four per cent of the pesticide business across Canada, he said, with the majority used in agriculture.