Hundreds of new sites possibly infected with tree-killing kauri dieback disease have been found by a sprawling, three-year aerial survey.

The joint-agency Kauri Dieback Programme has been running low-level flights across northern regions - taking nearly a million pictures and covering the equivalent distance of one circuit of the Earth - as part of its programme to monitor the soil-borne scourge.

After flying over around three million hectares, around 450 sites across Northland, Auckland and the Waikato were picked out as being possibly infected, of which three quarters consisted of single trees.

These sites - most of which were in Whangarei and southern Northland, southern Kaipara and Rodney - would be checked by teams on the ground.

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The only remaining areas to check from the air were Aupouri and Kaitaia in the north, but few, if any, potentially infected sites were likely to be found there.

So far, kauri dieback has spread throughout the Auckland region, the Coromandel, and to Waipoua Forest in Northland, the home of our most iconic kauri - Tane Mahuta.

Ministry for Primary Industries recovery and pest management manager John Sanson said infected kauri could be picked out by yellowing and thinning canopies.

"This may also be caused by other things such as drought, poor soil conditions, high winds, cattle and other animal movement under the tree," he said.

"In cases where kauri dieback disease is suspected, sites may be ground-truthed and soil samples potentially collected for laboratory testing."

Sanson said work was under way to speed up surveying and remote sensing techniques using high resolution satellite imagery, Lidar and hyper-spectral imagery were being trialled.

"By the end of this year we hope to know how feasible this might be and, if it is, how we can put this into operation."

Up to $180,000 was currently being spent each year by the programme on surveillance, which included everything from flying time, GIS mapping and data input, and lab analysis of samples, but not work by other groups and agencies.

Auckland Council's monitoring work included checking photographs and soil samples near potentially infected trees.

Its biosecurity manager, Phil Brown, said the council had prioritised extensive monitoring of kauri across the region.

"That means we can focus our resources on tackling the spread in affected areas and in keeping kauri healthy in those areas that are still disease free."

This month, the council also confirmed plans to close much of the Waitakere Ranges and high risk tracks in the Hunua Ranges to contain the disease.

Northland Regional Council was looking at its own ways to fast-track monitoring, and was assisting landowners who had found the disease on their properties, as was Waikato Regional Council.

The Department of Conservation (DoC) had meanwhile surveyed its entire 735km network of tracks through kauri forest it managed, and was three years through a plan it had developed.

That involved upgrading and re-routing tracks, closing some of them, and installing footwear cleaning stations at track entrances.

Two years ago, it piloted world-first prototype cleaning stations at four sites in Northland and the Coromandel, and extensive testing, monitoring and evaluation led to further improvements.

Forest & Bird wanted to see all public DoC tracks going through kauri forests, including Te Araroa, closed immediately until track upgrades and pig control lowered the risk of potential spread to an absolute minimum.

It also wanted an urgent focus on finding a cleaning solution that completely killed the spores - and of course, a cure for the disease itself.

Kauri dieback disease

• Kauri dieback disease is found in the upper North Island and can kill kauri of all ages. It is caused by a microscopic fungus-like organism called Phytophthora agathidicida.

• It lives in the soil and infects kauri roots, damaging the tissues that carry nutrients and water within the tree, effectively starving it to death.

• Soil disturbance from human activity like people using unofficial tracks or not cleaning footwear is one of the main ways spores can be spread.