Hadlock Field, Riverside Golf Course and 5 athletic field will be the only exempt properties when the ordinance takes effect July 1.

Beginning July 1, residents and city workers will no longer be able to freely use synthetic pesticides in Maine’s largest city, except in a few limited cases.

The City Council on Wednesday unanimously passed an ordinance regulating pesticide use in Portland. Advocates say it’s one of strongest anti-pesticide ordinances in the country, with scofflaws facing potential fines ranging from $100 to $500.

City staff estimates that the ordinance could cost up to $700,000 to implement. Those costs would cover new employees, equipment and up to a $250,000 set-aside to replace the turf on athletic fields.

The ordinance calls for a robust campaign to educate the public about ways to improve their lawns without using toxic chemicals.

Avery Yale Kamila, co-founder of Portland Protectors, a grassroots group that has lobbied for a strict pesticide ordinance for about two years, applauded the new rules Thursday.

“I’m so proud of the Portland City Council for passing one of the strongest organic land care ordinances in the country,” Kamila said. “The council listened to the residents, organic experts and the independent science and decided to prioritize public health and environmental stewardship. I expect our new status as a leading organic city will make Portland even more attractive to young people and visitors.”

Councilors voted 9-0 to approve the ordinance after a one-hour workshop that was followed by lengthy debate on 10 proposed amendments to the pesticide law.

Only two amendments passed, one of which set the ordinance’s start date for July 1. The other added an exemption for invasive insects.

“It was a lot of work that took place over a lot of months, but I think the people of Portland should be very proud,” Mayor Ethan Strimling said Wednesday night.

Councilor Spencer Thibodeau supported the ordinance, which is modeled after one in South Portland. It means that Portland will start using organic pesticides on all city-owned properties beginning this summer. The only exempt properties will be Hadlock Field, Riverside Golf Course and five high-use athletic fields that remain exempt until 2021.

“This is a really solid first step for the city of Portland,” Thibodeau said Wednesday.