We treated one batch of large P. radiata with 25% Grazon/75% Kwickin, and the other batch with 25% Grazon/75% Syntol.

Just completed the one-year monitoring visit. As expected from DOC’s basal bark work, the treatment is effective. The following chart shows the % dieback for single-stem Pinus radiata using the two different crop oils. All trees with a d.b.h of 700mm or less show at least 80% dieback, and it is anticipated that these should all show progressively more dieback over the coming 12 months. For larger trees, the result appears more variable, particularly using Kwickin, at this stage.

Mutliple stem trees also dying off, but most still have some green stems, particularly heavy lower branches. The prospect of achieving full dieback appears limited by the difficulty of getting full herbicide coverage on all stems – particularly those heavy lower branches that would not have been visible to the pilot. In fact, this appears the key limitation of the method – getting all heavy lower branches and stems treated and getting even coverage on stems, plus the pilot can’t detect small or subsidary trees.

On the native vegetation front, there has been a similar impact on the native vegetation from both products. Obviously any canopy plant that received direct contact with the chemical during the spray operation (either from drift or overspray) suffered dieback and usually died. Other more susceptible species below the canopy and in some cases a reasonable distance (up to 10m) from the target tree often showed signs of spray damage.

Susceptible species include Kanono Coprosma grandifolia, Twiggy coprosma Coprosma rhamnoides, Kamahi Weinmannia racemosa and Rewarewa Knightia excelsa . One year following the application of herbicides there was a notable lack of these species occurring as seedlings under trees that had been treated whereas they were still common beneath non treated species. We assume this is more likely to be a short term effect that will diminish over time. In the Kenepuru Head study site these species are, with the exception of rewarewa, amongst the most common species present.