In the Wilding Control Manual (for download click here), there are 15 techniques listed for controlling wilding conifers.  Five of those involve using herbicides:
•    stem poisoning
•    root uptake
and application via
•    foliage
•    cut stump surface
•    basal bark treatment

All five methods are described in the Manual, to which those wanting to undertake control should refer.  An excellent review on the use of chemicals was written by Pete Raal of DOC in 2005 (available from Pete Raal at DOC, Dunedin).  However, the herbicide mixes for some, particularly for foliage and basal bark application are still being evaluated.  Below is a summary of the current situation (as at May, 2010), with chemical recommendations where available.

The Department of Conservation has released two papers on herbicide application and more details on the TDPA mix and its application for distribution through the Wilding Conifer Management website. Click here

Stem poisoning

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.

Root uptake

This is a technique promoted by Bill Chisholm of Wilding Pine Control Ltd for small/medium sized trees in places which may be difficult to access.  For chemical details go to and refer to the Manual (download click here) for further comments, safety and audit recommendations.

Cut stump

This method can be useful on scattered, medium-sized trees on stony ground or with multiple stems.  Vigilant Gel is proven and safe – but expensive.  Metsulfuron, applied at 20g/litre is much cheaper, but its guaranteed effectiveness has yet to be confirmed.  Recently, a 20% Grazon in oil/diesel, has given good results on contorta pine (P. Raal, pers comm.), but once again, more time is needed for confirmation. Refer to the Manual (for download click here) for further comments, safety and audit recommendations.

Basal bark application

This is a new and simple technique with potential for killing wildings still in the ‘soft-bark’ phase of growth and up to medium-size (up to 15cm in diameter at their base).  Trials have been installed over the last 2 years (mostly by DOC), so no guaranteed recommendations can be made yet – although the mix of 20% Grazon in oil/diesel looks promising (P. Raal, pers comm.). Refer to the Manual (download click here) for further detail and also see this (Link) for the most recent news on this work.


Copied from email sent around by Pete Raal (DOC, Dunedin), 2/11/2010

Attached are my latest specifications for the basal bark spraying of willows (and most other woody species including pines, alders, elders, sycamores, hawthorns, cotoneasters, rowans, barberries etc) using a knapsack. All of the treated willows in the experiment (and some by-catch hawthorns and sycamores) have completely died.

A clearer description of the technique is given below.


As discussed at NETS last week, pines, sycamores and willows (and most other woody species) can be poisoned using low volume basal bark applications of Grazon (600g/l triclopyrbutoxy ethyl ester) herbicide. The technique is only really effective on trees with a stem diameter of less than 15cm and which have not yet developed a thick bark. As the trees become bigger, the bark becomes rougher and thicker and the technique becomes less effective (although I would try it on bigger diameter trees to see what happens - just spray higher up the stem for about 2m rather than just 40 - 50 cm). I killed a 20m high sycamore with a very thick trunk by spraying all the way around the trunk from ground level to as high as I could reach.


Basal bark applications of 200 millilitres Grazon in 800 millilitres petroleum-based oil or diesel should be used to poison the trees. For difficult to control species such as hawthorns, use 300 ml Grazon in 700 ml oil.


No water or water-based products such as dye, for example, must be added to the mix. This is because an invert emulsion will be formed which will clog up your knapsack. If you want/need to mark the trees you have treated, spray them with spray paint or mark them in some other way, just don’t use dye in the mix.


The technique is effective year-round for the selective control of unwanted pine trees and other woody species (i.e. it can be applied at any time of the year, including winter months, except when water or snow prevent spraying at the desired height above ground level - see below). Treatment should, however, ideally occur 6 weeks prior to leaf expansion until 2 months after to ensure the control of the root systems of targeted plants.

For best and reliable results, spray to saturate the entire circumference of the bottom 30 - 50 cm (up to 2 m for bigger trees) of trunk, including the root collar area, until just before the point of runoff using a knapsack (one dedicated for oil use only) and a solid cone or flat fan nozzle. Care must be taken to minimise the amount of spray drift and chemical/oil that runs into the soil which could potentially damage adjacent non-target trees. This is only because there is the possibility of injury to plants whose roots may extend into areas treated with the herbicide. Particular care must be taken to ensure that the oil does not get into water in a wetland situation (you may want to apply the solution using a paint brush in these instances).

The spray should not be used if there is "free water" on the trunks which would cause the oil/diesel to emulsify and run down the trunk without penetrating the bark. If this happens, a chemical girdle will not form and the control is unlikely to be complete. For this reason, spraying should not be done during or after recent rain or when there is frost on the trunks.

Triclopyr does not remain active in the soil for long where it is dissipated by microbial action into triclopyr acid.

Although much quicker and efficient than cutting and pasting, frilling or drilling and filling, basal bark treatments are labour-intensive because each and every stem needs to be treated. For this reason it can reasonably be expected that some trees and saplings will be missed during a poisoning operation. Follow-up operations should therefore be planned for missed stems, new saplings and root suckers. Usually one or two follow up spot treatments at 6-month intervals will provide a complete kill if the trees are susceptible. Re-treatment should include any living parts of treated stem(s) and re-sprouted stems.

Spray entire saplings with the brew to kill them.

If you use this method, please let me know how it all goes (practicality of application in your situation, effectiveness of the brews on your woody species etc) so that I can collate all the results/outcomes into a database that I am maintaining (This email address is being protected from spambots. You need JavaScript enabled to view it.). Please also bear in mind that the trees may take up to 1 year to die so don't draw conclusions too soon.

Foliar application

This is the most popular chemical wilding control technique, with the main determinant of success being the degree of foliar coverage/penetration achieved.  Hence, kills are not difficult to achieve on scattered smaller trees readily accessed by ‘nozzle’ pressure sprayers ( ground machine or helicopter mounted).  Mixes of metsulfuron (1g/10 l) and glyphosate (1%), plus a surfactant such as Pulse (1%), have been consistently successful.  However, this mix can cause considerable collateral damage to non-target species.  In this context, Reglone (10%) plus a surfactant (1%) can be used with far less collateral damage, but results on wildings have been more variable.

Boom spraying of conifers from the air has proven much more of a problem, with results characterised by considerable variability.  One exception is larch, which has not been hard to kill, but it is a different story for other conifers.  Hence, a series of new trials have recently been installed by DOC, Scion and ECan – employing a range of chemical mixes on contorta pine, dwarf mountain pine (P. mugo), Corsican pine and Douglas-fir.  The results of some of these look promising with the prospects of good conifer kills (particularly on Douglas-fir), but it is too early to be able to give recommendations confidently.  The most likely chemicals are also being tested for helicopter ‘nozzle’ spraying of lone trees.  Impacts on non-conifer species, especially native plants, have yet to be quantified.

In summary, it will probably be a year to 18 months before more reliable recommendations are available for the cost-effective spraying of conifers from the air.  Refer to the Manual (for download click here) for extra present-day detail.

Finally, a mention must be made of the growing international concern about the use of herbicides, particularly when applied extensively from the air - to the extent that aerial application is banned in places.  It is absolutely inevitable that this concern will increase in NZ, particularly as we depend on exports for our wealth – and they rely considerably on our maintenance of a ‘clean, green’ image.