Plant Pests (weeds)
Weeds are pest plants (usually introduced) that compete with productive plants (eg clover, grass, horticultural crops) or with indigenous plants. They compete by slowing their growth, shading them out or preventing regeneration of seedlings. Weeds can be controlled by physical removal (grubbing or cutting) or by herbicides (applied internally or externally).
In Nelson, gorse and broom are widespread, having been introduced and spread by early landowners and by animals and birds. The widespread use of fire to control pasture that was reverting to bracken and woody vegetation eliminated much of the competition for these weeds. The long-term viability of gorse and broom seed (more than 20 years in the ground) make it an extremely difficult plant to eradicate.
Controlling Weeds
Some weeds pose a much greater threat than others. Responsibility for controlling weeds that pose the greatest threat lies with Biosecurity NZ, a department of the Ministry of Agriculture and Forestry. Weeds that post a significant threat to economic or ecological values are usually included in regional pest management plans.
The Tasman-Nelson Regional Pest Management Plan lists 37 species of weeds under four different categories. These are weeds where the Council is satisfied that the costs of controlling them is justified by the benefits that this will bring. High-risk weeds with a very limited distribution are usually targeted for eradication. Weeds with a wider distribution may be progressively controlled to reduce their density and/or distribution. Widely-distributed weeds may be subject to boundary control to protect landowners with clean properties from being re-invaded from neighbouring properties.
The below brochures provide information on how to identify and control various pests, some of which are included in the Nelson-Tasman Regional Pest Plan
