There is good progress being made to determine the most cost-effective herbicides for controlling wildings. DOC is the main participant, led by Pete Raal (Dunedin) and Pedro Willemse (Twizel), and assisted by Stefan Gous (Scion, Rotorua). This summer they have installed well replicated trials testing what they hope will be the final herbicide mixtures to give >95% kill of contorta, Scots, Corsican and possibly mugo pine. The Grazon mix that has been giving >95% kill of contorta is the basis of all their brews. At the same time, Andy McCord of Technical Forest Services Ltd is applying his herbicide mixes (Pinox 5) using the same helicopter boom spray set-up and pilot. Hence, results of both approaches can be directly compared. Final results should be available in 18 months.
The basal bark herbicide method (Grazon and oil – for more info click here) has been working very well – to the extent that it is now being used operationally by many DOC staff. This method is also being tried for application from the air (includes large trees), but Pete says it is too early to be confident about giving a reliable recommendation. In the near future, DOC plans to hold a workshop for their staff, and to produce a best-practice manual. All information will be made available on this website once it is ready for such release.