The group wants the council to stop spraying around parks and road edges because children play there.
"My son was horrified when I told him, he said 'if they know it causes cancer why are they spraying it?', it's so easy when you're that little to ask," she said.
Similar campaigns were going on throughout New Zealand, but she thought the council was reluctant to use alternatives because of cost.
The trio said it was still early days and they collected 200 signatures in the first two weeks.
Mr Foster said the council used glyphosate-based agrichemicals for weed control but it was always open to discussing alternatives.
"We take guidance from the regional council and the Environmental Protection Authority, which regulates use of these types of substances in New Zealand.
"Products we use are currently considered the most efficient and cost-effective for weed management," Mr Foster said.
"We would be happy to talk about more environmental alternatives if that were wanted and if what we are using were proven to have severe detrimental impacts, we would look for other options."
Mr Foster said several factors needed to be balanced - council responsibility for providing a service, in this case weed control - efficiency and cost-effectiveness, and public health and environmental impact.
Options previously explored included using steam, although the practicality and cost had to date proven prohibitive.
"There are no formal complaints on record about council's use of glyphosate but we have had inquiries about our use of these products."
- For more information or to sign the petition go to www.tinyurl.com/j4qrcf6 or contact info@brownowl.nz
Where is it used?
* The council uses it along roadsides, spraying a 2m strip in rural areas to control vegetation for road safety purposes, kerbing and channelling and small areas around the likes of road signs. Roadsides in the lakes areas are not sprayed.
* Rotorua Contracting (formerly Castlecorp) uses glyphosate-based agrichemicals along and around fence-lines, retaining walls, bollards, hard surface edges and structures in parks and reserves. Spray cycles are carried out three to four times a year.