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New Zealand Journal of Forestry (1976) 21(1): 68–94
©New Zealand Institute of Forestry

Research article
The use of herbicides in forestry in New Zealand

C.G.R. Chavasse

This article summarises the papers presented and the discussion which took place at a symposium held at Rotorua in 1975. New Zealand Forest Research Institute Symposium No. 18, as with previous symposia, was concerned with defining the state of our knowledge as a basis for further advance. Summarised replies to questionnaires gave detailed information on current practice, and papers dealt with current research and recent developments; they also evaluated various aspects of herbicide use, including environmental aspects.
In nursery practice herbicides are used effectively with few problems remaining, although local refinements may in some instances be necessary.
In site preparation practice herbicides have become of major importance only over the last 6 or so years, and appear to have had a marked effect on the successful achievement of the goals of rapidly expanding planting programmes. Expertise varies, but adequate methods are available for the control of grass (whether or not grazing is to be undertaken in the developing stand) and for the desiccation of scrubweeds as an aid to burning. Where more difficult weeds are present, and the terrain allows, site preparation by machines is preferred, often supplemented by herbicides. So far, no entirely satisfactory operational herbicide techniques have been developed to control gorse, bracken, broom, and blackberry, although research results show promise. A great deal more elucidation of technical, physiological, and environmental aspects is considered necessary in this field.
Operations can be made more efficient by improved control and timing in relation to weather, time of day, and condition of plants. There is some dissatisfaction with equipment available for distributing liquids, and there is a need for development of precison gear for applying granules. Increasing interest is being shown in new methods of operating helicopters, in the use of vehicles for ground spraying, and in the use of manual tools — especially for ultra-low-volume sprays. New
* Scientist, Forest Research Institute, Rotorua



developments in the use of additives, such as thickeners and foaming agents, and in the possible use of granules, mini-granules, and micro granules, are also of considerable promise.
In the short term, at least, herbicides are considered, to be well-nigh indispensable tools for site preparation, although their replacement by specially-developed machines may be possible in the future.
There appears to be a need for expanded research into the use of herbicides in forestry in the following areas:
1.   Development of optimum regimes for individual weed types.
2.   Determination of environmental acceptability.
3.   Improvement of techniques and equipment for applying herbicides.
4.   Development of techniques for evaluation and interpretation of results in relation to the tree crop.
These broad objectives should be applied in conjunction with an economic evaluation of problem weeds to determine priorities.

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