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1384.6 - Statistics - Tasmania, 2002  
Previous ISSUE Released at 11:30 AM (CANBERRA TIME) 13/09/2002   
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Feature Article - Weeds

Feature article published in the Tasmanian Year Book, 1996 (cat. no. 1301.6)


WHAT IS A WEED

Broadly speaking, a weed is a plant growing where it is not wanted. However, a more useful definition of a weed is a plant which interferes with human activities or which may intrude upon or genetically contaminate indigenous vegetation.

In the past, weeds have been viewed as problems for mainly farmers and home gardeners. However, there is a growing recognition that weeds cause problems elsewhere as indicated by the following:

  • Pampas Grass and Blackberry are serious weeds of plantation forestry;
  • Cumbungi and Parrot’s Feather can block drainage and irrigation channels;
  • ivy is a known cause of dermatitis;
  • hemlock can poison animals and humans;
  • willow trees alter river flows, change water environments and reduce access for fishing;
  • toe-toe and broom are reducing the conservation value of the Southwest World Heritage Area;
  • Japanese Kelp is invading marine eco-systems on the east coast of Tasmania;
  • gorse is invasive of roadside strips, reducing the quality and extent of habitat for Tasmania’s native plants, birds and animals. These roadside strips contain roadside flora, and provide important migratory routes for some bird species and other native fauna;
  • interbreeding between plant species chosen for their ornamental value, and Tasmania’s indigenous species could threaten the genetic integrity of the latter, for example interbreeding of Eucalyptus globulus ‘compacta’ and the indigenous E. globulus.

DEGRADATION

In many instances, weeds are a symptom of land or environmental degradation. For example:
  • thistles may grow densely in pasture after desirable species have been weakened or eliminated by drought, insect damage or overgrazing; and
  • aquatic weeds may build up in dams and streams when artificial nutrients from fertilised pastures or dairy effluent contaminate the water. In these situations, remediation would focus on eliminating the cause or causes, rather than the symptom, the weed itself.

In these situations, remediation would focus on eliminating the cause or causes, rather than the symptom, the weed itself.

THE ECONOMIC COST OF WEEDS IN TASMANIA

An accurate estimate of the cost of weeds would include such things as the cost of weed control and the loss of primary production caused by weeds. Ideally it would also include the less tangible costs such as the loss of aesthetic and conservation values due to weeds or weed control measures.

An April 1994 estimate of the cost of weed control and loss of primary production was $33 million per annum in Tasmania. This estimate has been used as part of the Tasmanian Weed Management Strategy to help focus attention on the magnitude of the problem.

TASMANIAN WEED MANAGEMENT STRATEGY

The Tasmanian Government has established a Working Group to develop a strategic plan to increase the effectiveness of weed management in the State.

The Tasmanian Weed Management Strategy has been addressing existing and potential weed problems of major significance to primary industry, trade, human welfare, amenity, and biodiversity.

The Strategy covers weeds of all terrestrial and aquatic ecosystems in which plants may invade and/or have significant detrimental effects.

LEGISLATIVE ASPECTS OF WEED CONTROL

The Noxious Weeds Act 1964 (Tas.) empowers the Government to make land holders and occupiers control certain weeds. The Seeds Act 1985 (Tas.) aims to reduce the spread of certain weeds through contamination of agricultural seeds. The Fisheries Act 1959 (Tas.) controls the removal of marine weeds, such as Japanese Kelp. Other Acts that impact on weeds are the Biological Control Act 1986 (Tas.) and the Pesticides Act 1968 (Tas). All of the above Acts are administered by the Department of Primary Industry and Fisheries.

The following exotic weeds have been declared noxious under the Noxious Weeds Act:
  • Acroptilon repens (Creeping Knapweed)
  • Asphodelus fistulosus (Onion Weed)
  • Berkheya rigida (African Thistle)
  • Carduus nutans (Nodding Thistle)
  • Carthamus lanatus (Saffron Thistle)
  • Cenchrus incertus (Spiny Burrgrass)
  • Cenchrus longispinus (Spiny Burrgrass)
  • Chondrilla juncea (Skeleton Weed)
  • Cynara cardunculus (Artichoke Thistle)
  • Emex australis (Spiny Emex)
  • Equisetum spp. (Horsetail)
  • Homeria spp. (Cape Tulips)
  • Nassella trichotoma (Serrated Tussock)
  • Onopordum spp. (Onopordum Thistles)
  • Opuntia aurantiaca (Tiger Pear)
  • Parthenium hysterophorus (Parthenium Weed)
  • Pennisetum macrourum (African Feathergrass)
  • Solanum elaeagnifolium (Silver-leaf Nightshade)
  • Stipa caudata (Espartillo)
  • Xanthium spp. (Burrs)

Historically, weeds legislation has been aimed mainly at agriculture; however, several of the weeds listed above cause little if any direct detriment to agriculture. This policy reflects the current view that weeds legislation has relevance beyond agriculture.

Current Tasmanian Government policy recognises that weeds legislation has limited value in encouraging land owners to adopt long-term weed management strategies which can be achieved more effectively through community participation, such as Landcare.

TRAINING AND MANAGEMENT

Proper weed management requires the understanding of broad ecological concepts, as well as the knowledge of weed control methods. For example, the long-term control of thistles or capeweed in pastures is achieved more appropriately by encouraging competition from perennial pasture species rather than by use of herbicides.

Land managers must be able to obtain such information readily. Training must be available, adequately resourced and aimed at all people involved in weed management including operators of agricultural machinery and earth-moving equipment, landscape designers, nursery operators, and plant breeders.

Currently, bodies such as TAFE, the Tasmanian Rural Industry Training Board, the Department of Primary Industry and Fisheries (Whole Farm Planning Courses) and the Agriculture and Veterinary Chemicals Association (Avcare) provide training in weed identification, management and control for farmers, agribusiness and others.

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