Types of control methods

Introduction

There are four general methods of weed control used all around the world.

These are:

Integrated weed management

Integrated weed management combines the use of complementary weed control methods. This results in more effective, long term weed management outcomes.

It's recommended you use a combination of these four methods in an integrated weed management program.

Find out more about individual weeds and control methods.

You can also read the weed management handbook.


Biological control

Biological control, also known as biocontrol, involves introducing natural enemies of a weed, usually an insect or disease, to help manage it.

Biocontrol is an attempt to restore balance so that the weed does not have such an advantage over native plants. It is not an attempt to eradicate the weed.

A biocontrol program involves searching plants in their native country for any insects or diseases that appear to be damaging the plant.

Any promising agents are then tested for several years to ensure that they feed only on the target weed. Agents can only be released in Australia if they have gone through a very strict screening process.

For more information about the various biocontrol agents released in the Northern Territory (NT) see Appendix B of the weed management handbook.

Mimosa has been a key target for biocontrol in the NT since research began in 1979.

Fifteen different agents  - 13 insects and two fungal pathogens -  have been released against it and currently there are nine agents actively working to reduce mimosa growth, spread and seed production.

The root and leaf feeding beetle nessie (Nesaecrepida infuscata) has been very effective and is currently present in large numbers but only on restricted patches of mimosa.

If you are interested in assisting to spread nessie and introduce it to other mimosa infestations contact the Weed Management Branch.

The nine successful biocontrol agents currently working to control mimosa are:

Root and leaf feeding beetle (nessie) (Nesaecrepida infuscata)

Root and leaf feeding bettle (nessie) (Nesaecrepida infuscata)

Leaf feeding moth (Leuciris fimbriaria)

Leaf feeding moth (Leuciris fimbriaria) - adult

Leaf feeding moth (Leuciris fimbriaria) - larvae

Leaf feeding moth (Macaria pallidata)

Leaf feeding moth (Macaria pallidata) - adult

Leaf feeding moth (Macaria pallidata) - larvae

Root, seed and leaf feeding beetle (Malacorhinus irregularis)

Root, seed and leaf feeding bettle (Malacorhinus irregularis)

Green seed weevil (Chalcodermus serripes)

Apion weevil (Coelocephalapion pigrae)

Apion weevil (Coelocephalapion pigrae)

Carmenta (Carmenta mimosa)

Carmenta mimosa

Stem boring moth (Neurostrota gunniella)

Stem boring mouth (Neurostrota gunniella)

Seed feeding beetle (Acanthoscelides puniceus)

Seed feeding beetle (Acanthoscelides puniceus)

There are several species of sida in the NT. Spinyhead sida is the most common. It is a problem in tropical areas throughout the world where it competes with crops and pastures.

Calligrapha has been a very effective and useful biocontrol agent against spinyhead sida.

Leaf feeding beetle (Calligrapha pantherina)

Leaf Feeding Bettle (Calligrapha pantherina)

Salvinia is an aquatic fern that can completely cover waterways and reservoirs and can be a serious problem in northern Australia.

Biological control has been very successful, and only small amounts of herbicide are now required to manage salvinia.

Cyrtobagous salviniae

Salvinia infestation before treatment

Salvinia biocontrol treatment area after seven months

The parkinsonia biological control program is collaboration between CSIRO and the NT, Queensland and Western Australia governments.

Parkinsonia looper moth (UU and UU2) (Eueupithecia cisplatensis and Euecupithecia spp.)

UU has been a very effective and useful control agent in the NT.

Its close relative UU2 is currently being reared and released across northern Australia. UU2 comes from a warmer latitude than UU, which means that it may be better suited to the warmer conditions of northern Australia.

It also has a faster life cycle, which might make it faster at establishing a wild population and impacting on parkinsonia.

Eueupithecia cisplatensis - female (left) and male (right, (Photo Time Heard, CSIRO)

Noogoora burr is spreading along rivers in the Top End and the Kimberley, where it can form thick, impenetrable barriers to wildlife, stock and fishing.

It was one of the first weeds in Australia to be considered for biological control, and two agents have been released against it in the NT.

Stem galling moth (Epiblema strenuana)

Rust fungus (Puccinia xanthii)

Puccinia xanthii - Rust affecting a noogoora burr leaf


Chemical control

Chemical weed control uses herbicides and other chemicals to control weeds in specific situations, which are specified on the herbicide label.

Herbicides must be used according to the directions for use on the Australia Pesticides and Veterinarian Medicines Authority registered label.

For more information, go to the Australian Pesticides and Veterinary Medicines Authority (APVMA) website.

There are a variety of techniques and equipment available to apply herbicides.

The method chosen is determined by:

  • the type of weed and its growth
  • size of the infestation
  • access
  • resources available
  • personal preference.

Herbicide is mixed with water and often a wetting agent and applied to the leaves of plants using either hand-held spray packs or larger systems mounted on machinery.

This is an effective way to kill grasses and smaller woody weeds.

Foliar spraying of athel pine

Larger weeds are physically cut as close to the ground as possible using brush cutters, loppers, or chainsaws. Herbicide is applied immediately to the freshly cut surfaces of stumps or grasses.

This method helps to control the tree root system, and is especially useful in species that spread via suckers by preventing sprouting and regrowth.

Chemical application to cut mimosa stump

A wick or rope is soaked in herbicide and used to wipe or brush the chemical over the weed. This can be from a reservoir attached to a handle or it can be pumped to the wick using 12-volt equipment.

This is a useful method when killing a certain weed to avoid damaging surrounding plants.

Herbicide is applied directly to the soil beneath the weed and is taken up by the roots or the newly emerging shoots.

Oil soluble herbicide is mixed with diesel and sprayed around the full circumference of the trunk or stem of the weed. The diesel helps the herbicide to move through the bark and allows it to enter underground storage organs within the weed to slowly kill it.

This is an effective way to treat saplings, regrowth and multi-stemmed shrubs and trees.

Basal bark spraying of athel pine

A hole is drilled or cut through the bark of woody weeds and trees, and into the vulnerable sapwood tissue, and herbicide is immediately placed into the hole. The natural transportation systems within the weed then move the chemical through its tissues.

Demonstration of stem injection technique


Physical control

Physical weed control refers to manually removing weeds either by hand, or using tools or machinery.

Weeds, including their roots, are physically pulled out of the ground by hand or using hand tools.

This is an effective method of control for individual weeds and recent outbreaks that haven’t released seeds yet, but it requires a lot of labour.

A brush-cutter, slasher or mower are used to cut weeds off above the ground level. This can be effective in suppressing flower and seed development.

Slashing Gamba grass

A blade plough is used to push over some woody shrubs and cut their roots underground.

Example of a blade plough

Bulldozers, chopper rollers or graders are used to clear large weed infestations. This leaves large areas of soil exposed so follow- up control or revegetation is almost always needed.

Bulldozing chinee apple

A large blade with teeth attached to a bulldozer is used to clear large weed infestations.

This leaves large areas of soil exposed so follow-up control or revegetation is almost always needed.

A large heavy chain is dragged across the ground by heavy machinery to push over and pull out large weeds.

This method is useful for removing roots and providing access for burning. It works best at the end of the wet season when the ground is soft and roots are easier to pull from the soil.

Example of chaining


Land management methods

When weeds are present, they are part of a complex ecological system.

This system involves:

  • livestock
  • useful plants
  • native vegetation
  • wild animals
  • pest animals.

It also includes many other factors such as climate zone and landscape.

Managing so many factors can be very difficult and unpredictable.

Good land management techniques means understanding the ecological processes that affect weed growth and management and knowing how to use them to minimise their growth.

Unmanaged land can be affected by disturbances such as inappropriate clearing, overgrazing and uncontrolled fires. This can lead to weed takeover because the disturbances have left available space, sunlight and nutrients for the weeds to invade.

Removing stock from areas which have been treated for weeds is a common management technique used by land managers.

This can be done in short periods (pasture spelling), or it can be a reduction in stock numbers rather than complete removal.

Supplementary feeding will also reduce grazing pressure on the land and allow the re-establishment of desirable plants which will compete with the undesirable weeds.

Re-planting native vegetation or desirable pasture or crop species creates competition for the weeds that are present.

It is especially useful when weeds have been removed, as an established desirable plant will compete with the new weed seedlings as they emerge.

Fire as a management technique is more effective when it is used with other methods.

Deliberate controlled burning can be used to kill and remove some weeds. Either burning or preventing fire can manipulate the conditions to make them more suitable for the desirable species, allowing them to compete more effectively with the weed species.

The choice of whether to burn depends on lots of different factors.

Different fuel loads will create different fires that can either wipe out and destroy weeds, or in some cases they can scarify seed and induce weed seed germination.

Generally following an initial burn, fire should be excluded to give desirable plants and optimal conditions to establish and compete with any emerging weed seedlings.

Unmanaged fires can exacerbate weed establishment by burning hot and fast.

These fires cause minimal damage to the soil-stored weed seed bank, but can significantly damage native vegetation, which creates a perfect environment for post-fire weed regeneration.