Introduction
Why worry?
New Zealand's hill country pastures are important to the nation because they yield sheepmeat, beef and wool for export, and steep hillsides covered in grazed pasture characterise the New Zealand landscape. Hills covered in scrub weeds produce less and appear ugly and alien. Weeds even worse than gorse have not yet reached our shores. Accurate prediction of future weed problems allows us to prevent their entry into the country or, for those already here, to eradicate them or restrict their spread in hill country pastures.
Costs of weeds
Hackwell & Bertram1 recently put the economic losses in New Zealand from pests, weeds and pathogens at $440 million, and private and public sector pest control at $400 million annually. Weeds are particularly important in the pastures that form the basis of New Zealand's export markets in milk, meat and associated products. Gorse alone occurs on over 1214 km2 of land that could otherwise be in pasture.
New weeds
New species of plants constantly become naturalised in New Zealand from the 17,000 introduced plant species present in gardens or under cultivation, and from propagules brought into the country either accidentally or deliberately. Predicting which plants will become the pastoral weeds of the future is difficult at any time, but especially so when farming practices are changing rapidly, and climate change is altering weather patterns.
Prediction
Predicting future weeds is an imprecise science. A plant species may be present in the country for many years before its numbers and distribution, or changes in the environment, allow it to become an important weed. Such changes in the environment may be due to natural causes, such as warmer, wetter conditions, or may be caused by the introduction of different agricultural practices.
Scope of this report
This report deals with future weeds of hill country pastures, and covers some aspects of external and internal biosecurity. In pasture, plants are weeds if they are poisonous, unpalatable to livestock, or directly affect the quality of animal products. To invade pasture they must be able to germinate among and compete with pasture species. The report ignores 'weedy' grass species, like browntop or Kikuyu grass, that can be productive if well managed. Native species like manuka and matagouri are considered weeds because they interfere with pastoral production and controlling them can be expensive for farmers. 'Hill country' is here defined as 'uncultivable' land, with a slope in excess of about 20o.
Our report also explores New Zealand's legislation aimed at restricting the spread of weeds thought to be harmful, and reviews past and present weed research. Recommendations are made that could lead to improvements in the identification, tracking and early control of potential problem weeds, especially of hill country pastures.
Contact for Enquiries
MAF Information Services
Pastoral House
25 The Terrace
PO Box 2526
Wellington, NEW ZEALAND
Fax: +64 4 894 0721
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