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5.13 Herbicides
Authors: S GousPublication: , Volume Section 5 – Plantation silviculture, pp 13, Dec 2023
Abstract: There are many weed species in New Zealand plantations that can cause decreased tree growth and survival through competition for water, light and nutrients. Important weed species include: Buddleja davidii (buddleia), Cortaderia selloana and C. jubata (pampas), Cytisus scoparius (broom), Leycesteria formosa (Himalayan honeysuckle), Pinus radiata regeneration, a number of grass species, Pteridium aquilinum var. esculentum (bracken), Rubus fructicosus (blackberry) and Ulex europaeus (gorse). Forest vegetation management to reduce competition is often the single most important factor influencing survival and initial growth of crop trees. Controlling competing vegetation also improves stand access and reduces fire risk. Vegetation management should be well planned and integrated with establishment and silvicultural practices. Effective chemical weeding is superior to manual weeding and cover cropping (over-sowing with a benign cover species) when the costs and benefits of control are considered. Compared with alternative weed control methods, such as crushing, slashing and burning, the environmental impact from using herbicides is arguably minimal. Weed control methods should be compared in terms of efficacy, cost, and environmental impact. Potential longterm impacts must be assessed because under the Resource Management Act 1991 it is important that the forest resource is managed in a sustainable fashion.