Northern and Yorke
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Weed management on watercourses

This introductory guide and summary sheet has been prepared to help individual landholders and the community develop a plan for sustainable weed control activities in riparian lands. Riparian land can be defined in a number of ways, but put simply it is “any land which adjoins, directly influences, or is influenced by a body of water” (Land & Water Australia, 2007). This guide describes the biology and impact of the main weeds they are likely to encounter as well as the steps to develop a weed management plan.

Riparian land and weed management

The Northern and Yorke region contains four priority catchments: Willochra, Broughton, Wakefield and Light. These catchments cover an area of 1,460,000 hectares and contain native riparian vegetation corridors within a largely cleared landscape of primarily introduced species.

The catchments lie adjacent to each other in a north-south direction and include diverse riparian vegetation communities. Key watercourse vegetation types recorded across the catchments include: riverine forest/woodlands; riverine shrubland; chenopod shrubland; mangrove forest and samphire marsh; lignum swamp; sedgelands; reedbeds; and submerged aquatic vegetation.

These catchment areas support two nationally threatened ecological communities: peppermint box grassy woodland and iron-grass natural temperate grassland. There are currently also 25 nationally threatened plant species.

Weeds have become a serious threat to the ecological integrity and productivity of South Australian vegetation communities because of primary disturbances, such as vegetation clearance, fire and unsustainable stock grazing.

Habitat loss and degradation in riparian areas has also been caused by:

  • past native vegetation clearance
  • inappropriate grazing and browsing pressure from livestock
  • inappropriate burns
  • introduced pests
  • chemical use and pollution
  • revegetation with inappropriate species or seed sources
  • altered flooding regimes.

Weeds now dominate riparian areas throughout South Australia, including the Weeds of National Significance (WoNS): African boxthorn, bridal creeper, blackberry, boneseed and gorse. These are highly-invasive, high-impact weeds that are difficult to manage without a coordinated weed management program. To manage these weeds and declared weeds in the area, it is important to address the areas of degradation which encourage their establishment and implement a systematic control program with follow-up monitoring.

If weeds are neglected and become dominant, then the productivity and diversity of native riparian vegetation can seriously decline and the total cost of weed control is high. Prevention of weed infestations is far more cost effective than control. Most properties in the Northern and Yorke region have agricultural or environmental weeds that need to be controlled to some degree. The majority of these weeds were deliberately introduced from overseas, either as garden species or plants for agriculture.

Why should we manage weeds within the catchment?

Riparian land is an important part of Australian ecosystems because it is often the most diverse and productive part of the landscape. Riparian land contains a wide range of habitats and food types; is close to water; has a less extreme microclimate; and can provide refuge. There are many native plants found primarily or only within riparian areas. These areas are essential to many native fauna during their lifecycle, particularly in times of stress, such as drought or fire.

In-stream vegetation also plays a vital role in regulating healthy ecosystems for invertebrates within riparian areas. It provides shade that reduces light levels and water temperature and supplies energy and nutrients important to aquatic organisms as well as essential aquatic habitat.

Riparian areas provide a range of benefits in Australian ecosystems and this has been clearly recognised and valued in recent years.

Riparian ecosystems can:

  • improve water quality by trapping sediment, nutrients and other contaminants before they reach a waterway
  • lower water tables
  • reduce bank erosion and loss of valuable lands
  • control nuisance aquatic plants through shading
  • provide a source of food and habitat for watercourse animals
  • ensure healthy watercourse ecosystems
  • support sustained agricultural productivity
  • provide cultural and spiritual enrichment for people.

Today, weed invasion in riparian areas is a serious threat to local landowners and ecological communities. Riparian land that has become degraded by past land use, affected by flood or wildfire is at increased risk of weed invasion. Weed introduction can often be instigated through wind dispersal of seeds, seed deposition in the droppings of birds and animals, or the transport of seeds or vegetative material from upstream water.

Find out more about controlling weeds in the Northern and region.

Weeds of National Significance

  • Bridal creeper (Asparagus asparagoides)
  • Blackberry (Rubus fruticosus)
  • Boneseed (Chrysanthemoides monilifera)
  • Gorse (Ulex europaeus)

Declared weeds

  • African boxthorn (Lycium ferocissimum)
  • Wild artichoke (Cynara cardunculus)
  • Horehound (Marrubium vulgare)
  • Dog rose (Rosa canina)
  • Wild olive (Olea europaea)
  • Scotch broom (Cytisus scoparius)
  • Cape broom (Genista monspessulana)

Weed management

Prevention

Prevention is the first and most important part of weed management and represents good land management. This is true for both environmental and agricultural weeds as prevention is more cost effective than treatment.

To reduce the risk of weed invasion, landholders can:

  • sustain a mix of different native vegetation and ground cover, preferably a mix of trees, shrubs and groundcover
  • maintain wide and healthy native riparian vegetation colonies to resist drying winds, nutrient movement and the transport of weed seeds in bird droppings. The ideal width is least 25–50 m
  • eliminate stock from riparian land or use fencing to control the timing and length of grazing. Carefully managed grazing can be used to help control palatable weeds
  • avoid excessive human disturbance in riparian areas, such as constant vehicle access
  • cooperate with your neighbours to prevent infestation. Many weed invasions of relatively intact riparian vegetation have come from adjacent and upstream land
  • ensure vehicles, machinery and fodder is free of weed seeds before allowing on property.

Developing a weed management plan

It is important to develop a weed management plan for each particular site impacted by weeds. The most effective control is achieved when a variety of methods are used to target susceptible aspects of a weed i.e. lifecycle or environment.