Farm Forestry New ZealandAugust, 2015
Minimising the environmental impact of weed management in New Zealand’s planted forests
Field trials of herbicides in forest weed management were undertaken in this Sustainable Farming Fund programme. To retain Forest Stewardship Council (FSC) and other certification status, certified forests will need to continue to meet the criteria set by certification bodies. The work conducted has provided a comprehensive database reflecting the impact, efficacy and cost of available active ingredients for weed control.
Final report on field trials (pdf)
Weed Management book (pdf)
The designation of terbuthylazine and hexazinone as highly hazardous herbicides by the Forest Stewardship Council (FSC) in 2007 was the major driver for a programme of research initiated by forest owners in 2009. The aim of this programme was to identify alternative herbicides that could be used in planted radiata pine forests for weed control, particularly in the year of planting. New and already shortlisted alternatives to terbuthylazine and hexazinone were trialled in the field across a range of weed and environmental gradients with the objective of establishing successful operational prescriptions for use by all industry that were acceptable to forest certification bodies such as the Forest Stewardship Council.
Weed control in planted forests underpins highly productive, uniform forests and is one of the most important silvicultural tools when establishing trees in New Zealand. Weed control is normally provided by herbicides.
Environmental certification schemes place an onus on the planted forest industry to reduce or stop using some pesticides in plantation forests. Between 2007 and 2015, the herbicides terbuthylazine and hexazinone were classified as highly hazardous for use in plantation forests certified by the Forest Stewardship Council (FSC).
The New Zealand planted forest industry can minimise effects on the environment and meet environmental certification criteria by optimising herbicide application methods and using alternative, more benign, herbicides.
Weed management research at Scion over the last six years has largely focussed on finding alternative, less hazardous herbicides, as well as also investigating any negative environmental impacts associate with herbicide use. Methods to reduce the impacts of forest management on natural resources have been investigated, including targeted application of herbicides, dose optimisation and non-chemical weed control methods.
The research has shown that the most effective herbicide treatment to manage weeds in planted forests is the current industry standard that uses a combination of terbuthylazine and hexazinone. Both of these were recently re-assessed by FSC and removed from the highly hazardous list. The work has also shown that risks to the soil and water receiving environments from these two herbicides are low. Terbuthylazine mixed with mesotrione was the most promising alternative tested for first year weed control. Using the active ingredient aminopyralid as a replacement for picloram during the second year of weed control also shows potential.
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