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  Environment » Natural Resources » Biodiversity » Forest fragments » Managing forest fragments » Pest and weed control

Pest and weed control

Waikato’s forest fragments have a large boundary for their size, and are exposed to regular invasions from weeds and animal pests. Weeds can smother native plants, while animal pests browse native plants, and attack native animals or compete for their food supplies. Animal pests and weeds need to be removed from forest fragments so native plants and animals can thrive within them.Photo of two children clearing weeds from a forest fragment.

 On this page: Animal pests, Wily weeds

Animal pests

The impact of animal pests on forest fragments can be huge.

  • Possums mostly feed on leaves, but also eat young native birds and eggs, fungi and invertebrates such as insects.
  • Rabbits and hares are most common on open pasture, but will graze seedlings in small fragments and forest margins if the vegetation is not too dense.
  • In larger fragments, especially near large areas of forest, goats and deer can cause considerable damage. These animals eat seedlings, saplings, and the bark of trees within the ‘browsing zone’ (0.25 to 2 m above the forest floor).
  • Rats and mice feed on seeds falling to the forest floor. Rats can eat surprisingly large amounts of seedling and shrub foliage as well as bird eggs and invertebrates.
  • Stoats, ferrets, weasels, ship rats, possums, and wild (and domestic) cats kill many native animals in forest fragments.

For effective animal pest control:

  • Carry out pest control at regular intervals.
  • Extend control to surrounding farmland to create a buffer zone of low pest numbers and reduce the chance of them coming back into the fragment.
  • You can control animal pests with traps and poisons. However, make sure these methods don’t harm native animals in the fragment.
  • Talk to the Department of Conservation(external link) and Waikato Regional Council for advice on appropriate control methods. Always get permission from the Department of Conservation before using traps or poison on conservation land. 

Wily weeds

Early and repeated weed control may be necessary where they are common, and in forest fragments which have just been retired from stock grazing. Once you’ve got livestock out of the fragment, seedlings quickly begin to grow again. In heavily grazed fragments these may be invasive weed seedlings. If troublesome weeds are left to establish, more effort will be needed to remove or control them later.

Unless they are controlled:

  • Weeds like blackberry, pampas, gorse, broom and woolly nightshade can occupy ungrazed forest margins more quickly than native plants.
  • Weeds tolerant of low light levels will quickly cover the forest floor. This will smother native seedling growth. Such weeds include wandering dew, wild ginger, ivy and periwinkle.
  • Introduced climbers like old man’s beard, Japanese honeysuckle, and climbing asparagus will smother and kill trees in fragments damaged by grazing.

For effective weed control:

  • When working with spades and machinery in weedy areas, wash them down before using them elsewhere on the farm so you don’t spread weeds. Fencing out stock will also reduce the spread of weeds.
  • In small areas, control weeds by hand pulling, digging and cutting. However, in larger areas, and where weed invasion is substantial, herbicides may be the only practical means of control.
  • Ask your local plant pest officers, the QEII National Trust(external link), qualified contractors or Department of Conservation(external link) office, about herbicides before you buy.
  • Use chemicals that are proven against the weed you are targeting, and always apply them at the recommended rates.
  • Native plants are sensitive to most herbicides. Avoid spray drift by spraying only when there is little or no wind. Place a spray cone over the nozzle. Don’t use chemicals that remain active in the soil for long periods near native plants, or where natives are in the path of water running off nearby land. Follow the label's stand down period between spraying and planting.
  • If natural regeneration does not readily occur, plant native trees and shrubs in the understorey, especially at the edges, to increase shade and deter weeds. See the planting guide for suitable species.
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