The identity of the person who poisoned hundreds of roses in Dunedin's Northern Cemetery last year looks set to remain a mystery. More were poisoned recently.
The Dunedin City Council says tests of the poison, Picloram, showed it was not used by contractor Delta, and the recent poisoning happened after Delta stopped its weed work at the cemetery.
Picloram is used in brush-killer products like Tordon and Metsulfuron, and "those particular products aren't in use by the contractor on that site'', the council said.
But Heritage Roses Otago convener Fran Rawling has questioned how the council could conclude it was not Delta.
Roses at the Northern Cemetery were sprayed with herbicide late last year.
About 500 roses, more than 40 per cent of about 1200 at the cemetery, showed signs of damage, including memorial roses planted by families of those buried at the cemetery in the 1800s.
Council soil and foliage tests were "inconclusive" said acting group parks and recreation manager Tom Dyer'.
However, he said it was unlikely the contractor poisoned the roses.
"A number of other things point away from contractor error, including the nature of spray damage, the location of spraying and the contractor's long-time experience managing the cemetery.''
Delta had not sprayed at the cemetery since the damaged roses were discovered.
More damage happened recently, and the areas affected and pattern of damage indicated someone "may have caused damage unintentionally when spraying a loved one's grave''.
Dyer agreed it was unlikely last year's damage was done the same way, as it was widespread and affected roses across the cemetery.
Delta did edging around graves and pathways and ornamental gardens, and the spray damage had been "a long way away from those areas''.
Heritage Roses Otago and Delta had told the council about the recent spray damage, which had happened some time over the past couple of weeks.
That herbicide damage to rose plants had "clearly'' been done by someone with a sprayer in the cemetery who had walked along with spray dripping from a nozzle.
"That's not what I'd expect from our contractor; all their gear is well maintained, and we don't see that on other sites,'' Dyer said.
He said it was possible the two lots of damage were not linked, and was confident a Delta employee was not involved last year.
Dyer said the council was doing everything it could to find who was responsible and make sure the problem was not repeated, but it still had "a way to go''.
A growing trial of peas in affected soil was under way to ensure any new rose plantings would not be affected.
Rawling said she was not sure how the council concluded Delta was not at fault.
"I would certainly query where that came from; how did they come to that conclusion it's not likely to be a contractor?''
Delta's contract said employees were not to spray near roses, and had to weed by hand, but "there is a lot of evidence of a nozzle going under a rose and round a trunk, and we've got photographic evidence of that, and so have they.''
Rawling said some of the roses had made a comeback, but "a lot'' had not and some had died.