Most of the expensive nikau palms in Queen St are malnourished, full of bugs and will die without urgent care, says a tree expert.

Graeme Platt, an authority on New Zealand native plants, said that without proper feeding and insecticide to kill the bugs, Queen St will become a "tatty mess" of dead trees within three or four years.

All up, 47 nikau palms were planted in 2007 at a cost of $454,000. To give them the best chance of survival, they were placed in specially designed pits with 8cu m of soil, drainage holes in the bottom, grills at ground level for irrigation and coils to feed water to the tree roots.

Twenty-five palms came from a farm near Karamea, on the West Coast. Farmer Selwyn Lowe sold the palms for $562.50 each but by the time they were removed, transported and maintained by the Specimen Tree Company, they were sold to the council for $8800 each. The company provided another 18 nikau from Taranaki and four from other sources.

In June last year, a palm near the bottom of Wyndham St died from a fungal disease and was replaced.

Mr Platt said thinning of the trunk where it met the bulb of the palms was a bad sign of stress and led to mite, scale and mealy bugs attacking the fronds.

"If something is not done quickly, the council are going to have dead ones on their hands," he said.

Mr Platt said the solution was to give the palms regular liquid feed and liquid insecticide to kill the bugs. Spraying the palms with "environmentally unfriendly" insecticide in Queen St was not an option.

Oratia Native Plant Nursery owner Geoff Davidson agreed with Mr Platt that thinning of the nikau trunks was a sign of stress, probably caused by shifting mature plants from their natural habitat to an urban environment.

Auckland City CBD project manager David Jones said council arborists acknowledged there was a problem with bugs and were evaluating insecticide products to address the issue.

Other than that, he said, the council was looking after the palms in accordance with the tree maintenance plan for Queen St and they were fine. This included watering each palm pit weekly with 80 litres of water and more in dry periods.

Former president of the Palm and Cycad Society of New Zealand Terry Behersing said in his opinion the palms along Queen St were doing well.

"If you look at the top of them they are sending new fronds out. The leaves on the side are getting tacky and falling off but that's normal. The palms are adapting well to their new environment."

Stuart Barton, of the Specimen Tree Company, said his company had a 12-month maintenance contract for the palms and was no longer responsible for them.

The palms were planted amid fierce debate. Some Aucklanders believed the removal of the existing exotic plants would amount to downgrading Queen St. In the end the council removed 17 exotic plants.