A weed is any plant that colonises and persists in an ecosystem in which it did not previously exist. They may affect the economy, the environment, human health and amenity. Many plants introduced into Australia in the last 200 years are now weeds.

Plants that are weeds have a number of common characteristics. They usually produce large numbers of seeds. They are often excellent at surviving and reproducing in disturbed environments. They can usually thrive in a variety of conditions.

A weed can be an exotic species or a native species. Weeds can inhabit all environments; our cities, deserts, waterways, alpine areas and oceans.

Weeds invade bushland, particularly where there has been some disturbance to the natural processes in that environment, and can out compete native plants.

Throughout Australia, weeds are spreading faster than they can be controlled and management of them is consuming an enormous amount of resources. Some weeds are of particular concern and have been listed for priority management in legislation.

Not all of Australia’s weeds have come from other countries. Australian native plants can also become weeds. This usually occurs when species move into new areas where they have a competitive advantage over indigenous plants. An example of a native plant establishing itself outside its natural range is the Cootamundra Wattle Acacia baileyana.

Useful links for weed identification

Weeds in Australia, home page
https://www.environment.gov.au/biodiversity/invasive/weeds/

Weeds Australia, Weed ID page
https://www.environment.gov.au/biodiversity/invasive/weeds/identification/

Weeds of National Significance
https://weeds.ala.org.au/WoNS.html

New South Wales

NSW WeedWise
https://weeds.dpi.nsw.gov.au/

Sydney Weeds Committees
https://sydneyweeds.org.au/

Victoria

Agriculture Victoria
http://agriculture.vic.gov.au/agriculture/pests-diseases-and-weeds/weeds/a-z-of-weeds

Declared Noxious Weeds
http://agriculture.vic.gov.au/agriculture/pests-diseases-and-weeds/protecting-victoria/legislation-policy-and-permits/declared-noxious-weeds-and-pest-animals-in-victoria

Queensland

Weeds of Australia identification tool
https://www.business.qld.gov.au/industries/farms-fishing-forestry/agriculture/land-management/health-pests-weeds-diseases/weeds-diseases/identification

Weed Management

Weed Management Guides
http://www.aabr.org.au/learn/professional-practice/management-guides/

NSW DPI Weed Management Guides
https://www.dpi.nsw.gov.au/biosecurity/weeds/weed-control/general-management/weeds-crc-pubs/wmg 

NSW Weed Control Handbook
https://www.dpi.nsw.gov.au/biosecurity/weeds/weed-control/management-guides/noxious-enviro-weed-control 

Invasive Species Council: A whitelist approach
https://invasives.org.au/publications/stopping-weed-invasions-white-list-approach/

Regulatory Requirements for Chemical Use

Pesticide Use in NSW  : legislation, training, re-training, record keeping and minor-use permits
https://www.epa.nsw.gov.au/your-environment/pesticides

Pesticide Use in Victoria : A guide to using agricultural chemical in Victoria :  legislation, training, licences, notification, record keeping
http://agriculture.vic.gov.au/agriculture/farm-management/chemical-use-old/publications/a-guide-to-using-agricultural-chemicals-in-victoria