TORONTO - Premier Dalton McGuinty is dismissing calls to change Ontario's proposed pesticide ban to allow municipalities to keep tougher laws, despite concerns that the new standard will weaken local bylaws that are protecting people's health.

McGuinty, who admitted he "screwed up'' when he said municipalities could enact stronger anti-pesticide bylaws, said Tuesday he's determined to bring in a "single, solid, safe and effective'' provincial standard.

"We're banning both the sale and use (of pesticides),'' he said.

"I think that takes us considerably further than any municipal pesticide bylaw. But we'll sit down and we'll talk to the cities and make sure we're getting it right.''

Ontario's proposed ban on the sale and cosmetic use of pesticides, which is expected to take effect next spring, was heralded as the toughest such legislation in North America when McGuinty announced it on Earth Day last month.

But supporters are now concerned the bill will water down stronger protections that municipalities already have in place.

Dr. David McKeown, Toronto's medical officer of health, is urging the province to change the bill to allow the city's restrictions to stand if they differ from Ontario's proposed ban.

He warns that if the wording isn't changed, some residents may end up receiving less protection from pesticides under the provincial ban than under city bylaws.

"This does take away the opportunity for local jurisdictions to enact restrictions on pesticide use that make sense,'' McKeown said.

The weed-killer glyphosate, which is sold under the brand name Roundup, has been banned by Toronto, Markham and Peterborough, said Gideon Forman, executive director of the Canadian Association of Physicians for the Environment.

But the herbicide isn't included in the province's draft list of more than 300 banned products, he said.

"If a municipality wants to go beyond the provincial ban and do something extra to protect its citizens, we think that they should be allowed to do that,'' Forman said.

Some municipalities would also like to restrict the use of pesticides on golf courses, which are excluded from the province's ban under certain conditions, Forman said.

Another exception in the bill allows pesticides for "other prescribed uses,'' which could permit the use of pesticides to control weeds, he said.

"Overall, the thrust of the legislation is great,'' Forman said. "There are some loopholes, the municipal powers one being the biggest.''

McGuinty, who initially said municipalities could impose tougher standards than the province, has since admitted he was wrong. But he spread the blame to Environment Minister John Gerretsen for being "unduly deferential'' and not correcting the mistake immediately, instead of days later when the error came to light.

Opposition parties say McGuinty should make his gaffe part of the legislation and give municipalities the power to decide what's best for them.

"He's made a huge deal about this pesticide act,'' said NDP critic Peter Tabuns.

"His representatives and ministers present it as the best thing since sliced bread _ almost a millennial achievement. And yet, he's actually going to be rolling back standards in cities like Toronto. It makes no sense to me.''

Under the legislation, 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.

Quebec, the only other province to have banned pesticides, was considered to have the toughest standards on the continent. The final phase of its Pesticide Management Code, first introduced in March 2003, went into effect in 2006.