What is a weed?
A weed is a plant growing where it is not wanted. A plant that is considered a weed in one situation may not be considered a weed in other contexts.
Weeds are generally unwanted in a particular situation because they threaten agricultural productivity, have detrimental effects on the natural environment or impact on human health.
Weeds are often classed into broad groups depending on their characteristics, impact and the situation in which they grow.
- noxious weeds
- weeds of national significance
- waters weeds
- other weeds
Many weeds can be classed in more than one of these groups. For example, blackberry can be classed as a noxious weed, an environmental weed and an agricultural weed, depending on the situation where is it occurring. It is also listed as one of Australia's Weeds of National Significance. Some cultivars are also grown for commercial blackberry production or in domestic gardens for berry harvest.
Where do weeds come from?
Most of our weed problems originate from parks and gardens and were inadvertently introduced. Other weeds come from the introduction of plants for agricultural production, for aquaria, as contaminate of goods or from other sources.
About 20 new foreign species are discovered growing in the wild in Australia each year.
Increasingly, scientific weed risk assessment processes are being used to lessen the likelihood that the introduction of new plants will result in weed problems. Within the nursery industry the invasiveness of 1000 plants grown and sold in Australia has been assessed. The nursery industry has also produced information to assist gardeners with appropriate plant choices for their area.
Some serious weeds are required by law to be controlled by land owners and occupiers. These weeds are noxious weeds. A weed is declared noxious because controlling it provides benefit to the community over and above the cost of implementing that control.
In order to determine which plants are noxious weeds a scientific process of weed risk assessment is undertaken at a local, state and national levels.
In New South Wales the administration of noxious weed control is the responsibility of the Minister for Primary Industries under the Noxious Weeds Act 1993.
The Act is implemented and enforced by the Local Control Authority (LCA) for the area, usually local government. The local government invests significant resources and time in order to protect NSW from the spread of noxious weeds.
Weeds of national significance
Thirty-two weeds of national significance have been identified by the Australian Government under the National Weeds Strategy. They are identified based on their invasiveness, potential for spread and environmental, social and economic impacts.
Twenty-eight environmental weeds are listed as national environment alert list weeds. These are non-native plant species that are in the early stages of establishment and have the potential to become a significant threat to biodiversity if they are not managed.
Freshwater ecosystems are highly vulnerable to invasion by water weeds. Since European settlement many exotic weed species have been accidentally or deliberately introduced into NSW waterways, and have become widespread.
There are many others weeds that impact on horticulture, agricultural production, the environment, gardens or on amenity.