Good trials have been carried out by DOC and Scion - plus the Marlborough Sounds Restoration Trust is using this technique to control thousands of mature wilding trees. Either Glyphosate (see P. Raal’s chemical review) or Metsulfuron-methyl can be used.
The current chemical of choice is Metsulfuron-methyl, and the ‘one-mix-for-trees-of-all-sizes’ recommendation is 10gms Metsulfuron-methyl, either as pure ‘Meturon’, or in a 600g/kg concentration (for example, Escort, Matrix or Zeal) per litre of water. It is important that the pH of the mixed solution is 7 or greater, and this will vary with the product used and the source of water (creek water often less acidic than rain water). Remember, the more acid the solution the poorer the results. This must be fresh (mixed daily) as the chemical loses its effectiveness quickly. Apply (squeeze bottle / pump pot / drench gun) 25mls of the mix into 20mm diameter x 50mm deep holes, spaced at 50cm intervals around tree trunks at 30-50 cm above ground level. This technique works well on radiata pine, although holes may have to be placed closer on the biggest trees (1m+ diameter) with huge green crowns and a number of large branches. The Metsulfuron brew has yet to be fully proven on other conifer species. Refer to the Manual (for download click here) for further comments, safety and audit recommendations.