Weeds are considered to be any plants, native or exotic, that are growing where they are not wanted. However, there are also specific regulations around specified invasive plants as they may be prohibited or restricted in Queensland. In terms of aquatic ecosystem management, vegetation has many benefits, such as providing habitat and increasing the strength of the substrate. There are situations where vegetation has negative implications. Examples include where vegetation has grown more abundant compared to its reference condition or its establishment has changed the boundary conditions such as the strength or roughness of the river channel. The consequences of these can be that native vegetation is outcompeted or that the rates and location of erosion and deposition are altered. All these impacts can result in a loss of habitat.
Other general information on weeds and their management is available from sources such as the Commonwealth Government's list of Weeds of National Significance.
Landowners are responsible for taking all reasonable and practical steps to minimise the risks associated with invasive plants under their control. This is known as the general biosecurity obligation (GBO). Your local government has a biosecurity plan that outlines everyone’s role and responsibilities in managing specified invasive plants.
Abundant growth of native or invasive species can often occur in situations where the nutrient status or flow regime of the water has changed. The hydraulic roughness characteristics of the vegetation need to be considered as well as its spatial arrangement. Vegetation that becomes prone during floods may have less of an effect on the flow and sediment than vegetation that remains upright. Equally, patchy vegetation along or in the channel may be less of an issue compared to growth across the whole channel cross-sectional extent.
The growth form of weeds is also important and may impact beneficiaries of the river. Submerged weeds can impact pump infrastructure whilst floating or emergent weeds can impact recreational use and amenity. The complete life cycle of the vegetation, and its succession, needs to be considered. For example, an increase in leaf area cover can alter the amount of sunlight reaching the water, and its subsequent death can increase organic matter in the water changing the water quality.
Examples of different weeds that have very different locations, forms and subsequent effects are:
Weed control can be conducted within all zones of a river system including terrestrial riparian areas adjoining river channels, exposed streambank and streambed within the channel and instream aquatic areas. The channel morphology and weed location can help guide the appropriate weed control actions. Aquatic weeds can include submerged or floating plants and emergent plants on the wet channel margin. Aquatic weed control is generally quite distinctive to terrestrial weed control. There may be greater sensitivity to issues of water quality and biota impacts, chemical use, access constraints, and reinfestation potential associated with water borne propagules from upstream source areas.
The main methods of weed control include:
Fire, such as controlled burns, can be used to kill both the weed and its seeds, reducing reinfestation. Most species of invasive aquatic grass weeds, including Hymenachne and Para Grass, are fire sensitive. In seasonally dry climates the introduction of controlled burns in riparian areas can help to both control grass weed infestation levels and promote native macrophyte species. These burns require careful management so they do not end up out of control.
Crash grazing, where stock are allowed onto the site for a short timespan to limit trampling and other impacts, may be a control strategy. Grazing strategies can be put into a farm management plan so that assisted revegetation is not adversely impacted. Environmental flows may be used to change the water regime and water quality to remove/reduce weeds and promote native vegetation.
Removing vegetation from within a river channel presents a range of potential impact risks including generating channel or bed instability, water quality degradation and habitat loss. These risks need to be assessed alongside the possible reinfestation of the site. If the cause of the infestation is external to the site, such as a changed flow or sediment regime, then this needs to be addressed.
Potential benefits from this intervention:
Potential negative implications from this intervention:
Chenoweth EPLA and Bushland Restoration Services. 2012. South East Queensland Ecological Restoration Framework: Manual. Prepared on behalf of SEQ Catchments and South East Queensland Local Governments. Brisbane.
Queensland Agriculture Using trees to control weeds- passive revegetation - YouTube
Queensland Government Weeds and diseases information
Last updated: 28 June 2022
This page should be cited as:
Department of Environment and Science, Queensland (2022) Weed management, WetlandInfo website, accessed 1 July 2022. Available at: https://wetlandinfo.des.qld.gov.au/wetlands/management/rehabilitation/rehab-process/step-4/intervention-options/weed-management-mod.html