Premier Dalton McGuinty says he won't change Ontario's proposed pesticide ban to allow municipalities to keep tougher laws.

He says the province will have a single standard that bans both the sale and use of pesticides, which goes further than any municipal bylaw.

But there are concerns that some residents could be less protected from pesticides under the province's ban than under existing bylaws.

Toronto's medical officer of health says the provincial ban doesn't include a common weed killer that's prohibited in Toronto, for example.

Dr. David McKeown is urging the province to change the legislation to allow the city's restrictions to stand if they differ from Ontario's proposed ban.

McGuinty was forced to admit last week that he "screwed up" when he said municipalities could enact tougher bylaws than the province when he announced the pesticide ban on Earth Day.