Department of Conservation (Doc) Twizel ranger Peter Willemse said wilding conifers were a serious and dramatically expanding problem in New Zealand - sucking up water, crowding out native species, increasing fire risk and destroying landscapes.
''Sadly, the spectacular open grasslands of the Mackenzie are especially vulnerable to invasion from conifers,'' Mr Willemse said.
He and Dunedin-based Doc technical adviser Pete Raal have been working together for six years to develop an effective method of dealing with the overwhelming issue of dense wilding pine infestations in the region.
The pair are carrying out helicopter boom-spraying using a herbicide blend dubbed ''Armageddon''. Trials using the blend on Pinus contorta last year proved fatal to 98% of the trees.
Mr Willemse said Doc had high hopes it would have the same impact on Pinus mugo, which also threatens the Mackenzie District's ecology.
Mr Raal said using this control method, pines would not re-establish beneath the canopy, but native plants would.
''We've discovered that as well as removing the pine tree threat to this area another positive consequence of using this technique has been that there is low pine regeneration because they are shade intolerant, but our native plants do really well in the filtered shade environment under the sprayed trees,'' he said.
The Doc team planned to spray areas of pines in Diadem Creek, where they were a threat to Ahuriri Conservation Park, and larch in Jollie Valley, at Aoraki/Mt Cook National Park.
Both are areas where pest trees have established a stronghold.
They are also carrying out trial spraying on pines near Lake Pukaki.
''Time is not on our side as the cost of controlling wilding conifers escalates over the years,'' Mr Willemse said.
''However, they are a pest problem that New Zealand is able to overcome. We have developed good control methods which, combined with strong community support, should ultimately allow us to win the war against them.''
