Six alternative methods for combating weeds in the city will be put to council at a meeting tomorrow.
The council is responsible for weed and vegetation control within road corridors, parks, reserves, cemeteries, landfills and around infrastructure.
It could consult with residents whether to adopt a mix of manual and mechanical methods, thermal control and organic sprays or to maintain the status quo.
A report to be tabled at tomorrow’s meeting listed manual pulling, mechanical removal, mulching, thermal control, organic sprays and chemical herbicides were all on the table as options.
The current method used by DCC contractors is a herbicide spray, glyphosate, which is the most widely used herbicide in the world and in New Zealand.
Staff cited a 2015 report by the World Health Organisation that classified the chemical as "probably carcinogenic to humans", based on limited evidence of cancer in humans and sufficient evidence in animals, and a 2016 NZ Environmental Protection Authority review that concluded glyphosate was unlikely to be carcinogenic to humans and did not need to be classified as a carcinogenic or mutagen.
The report stated that all conversations with experts supported the conclusion "organic sprays are significantly less effective and significantly more costly than glyphosate products".
A trial conducted by staff found an organic herbicide would need to be sprayed three times more at a cost 14.6 times that of glyphosate.
The increased cost to maintain a level of weed control comparable to that of the current herbicide was estimated at between $4.1 million and $5.3m for all options, accounting for increased usage.
Additional funding would be required for all other options, while the current method was "considered by some to have adverse environmental and health effects", the report said.
Council would continue its discussions on its preferred option at its 10 year plan consultation next year.
tim.scott@odt.co.nz , PIJF cadet reporter
