Control techniques

Hand removal

Hand removal is labour intensive, which may be expensive. However, it limits disturbance to other desirable plants and the soil. It is suitable for small or scattered infestations.

Weeds may be hand pulled or dug out using tools such as shovels, hoes or mattocks. Hand removal is also useful as a follow up method after other treatments. Removal is often easier after rain when the soil is softer. Appropriate protective clothing should be worn especially when dealing with thorny, prickly or poisonous plants.

Crowning

A knife or sharp trowel is used to cut away all of the roots from the central crown. The crown is then levered out of the ground. This method is useful for many weedy asparagus species.

Raking

Ground cover weeds (e.g. trad) in sensitive bushland sites can be raked. The weeds are raked into a pile and can be treated by covering in plastic mulch or using herbicides.

Follow up is often necessary to treat any missed fragments that have regrown.

Biological control of weeds uses a plant’s natural enemies such as insects, mites and plant diseases to reduce infestations. It is an economical and environmentally sound method. However, it is a long-term method and may take many years to be effective. Biological control agents are safe to use. Extensive trials check that they do not harm any desirable plants including native plants or crops.

Biological control is most suitable for larger infestations of widespread weeds such as Patterson’s curse, many cacti and salvinia. Biocontrol reduces the infestation but does not eradicate the weed.

Biological control agents are released onto the weeds at sites with large infestations. Do not use other control methods on the release site. This is so the biological control agent’s population can increase with a large food supply. Monitor the size of the population and the impacts of the agents at the site. More releases may be needed, or the site could become a collection site.

A few biological control agents are applied like herbicides. This includes plant diseases such as rusts and fungi applied as a treatment. An example is the capsules that can be inserted into Parkinsonia.

Contact your local council weeds officer for advice about using biological control on weeds.

Carefully dispose of all seeds and any plant parts that can regrow. Some weeds can be buried deeply, e.g. cacti need to be buried at least one metre below the surface. A hot fire can be used to burn some plants and kill the seeds. Whichever method is used, disposal sites should be checked regularly for new plants or regrowth. For advice about off-site disposal, contact your local council.

Mechanical removal

Large machinery such as backhoes and bulldozers can be used to dig out large infestations of weeds. They can be useful for woody weeds and large prickly weeds such as cacti.

Machinery is most suitable for flat easily accessed areas away from native vegetation.

Disadvantages of using large machinery include:

• causing soil erosion
• creating ideal conditions for new weeds to grow
• soil compaction in wet conditions.

Permits may be required for using machinery to remove plants, especially along waterways. Contact NSW Local Land Services for advice on the required approvals for your site.

Aquatic weeds

Mechanical removal of aquatic weeds includes using:

• Floating broadscale harvesting machines in waterways with dense infestation of weeds such as Salvinia.
• Scoops attached to the bow of small boats.
• Amphibious vehicles that can access shallow areas. They can rake, cut and harvest weeds.
• Suction based harvesters can suck floating weeds or cut and suck anchored aquatic weeds.

Cultivation

Cultivation is particularly effective on young weeds. It breaks the weeds into pieces and separates shoots from roots. Some cultivation techniques bury the weeds deep enough so they cannot regrow. Other techniques pull all of the weeds to the surface so they can dry out and die. Use the correct implements for the desired result.

Cultivation is more effective if weeds are cultivated before they flower and during dry conditions.

Some types of weeds can be controlled with repeated cultivation. Perennial weeds may be difficult to control with cultivation, especially those that easily shoot from root or stem fragments.

Slashing and mowing

Slashing is cheaper than cultivation. It preserves ground cover, reducing soil erosion and allowing access in wet weather. Slashing is suitable for pastures and between rows in orchards.

Slashing will not usually eradicate weeds. Continual slashing may provide control if a desirable pasture species or other ground covers outcompete the weeds. Slashing can:

• prevent tall weeds from flowering and seeding
• remove unpalatable or inedible weeds left after stock have selectively grazed a paddock
• temporarily control weeds until they re-shoot
• control vegetation and weeds along roadsides
• provide access through large, dense infestations so that other weed control methods can be carried out e.g. slashing paths through lantana to give access for people using splatter guns.

Slash before weeds fruit, to prevent the spread of seeds. Avoid slashing plants that can grow from stem fragments and be spread by slashers. Slashes and mowers should be cleaned before moving between sites.

Mulches exclude sunlight, which prevents or reduces weed growth. Mulches may be expensive and are only suitable for some situations. Mulches include:

• black plastic which is used between low-growing crops such as strawberries and to treat environmental weeds such as trad in natural environments
• woven weed matting, which is useful along roadsides, steep banks and cuttings where areas need to be revegetated or stabilised
• organic matter such as woodchips, straw, grass clippings, paper, cardboard, sawdust or manure, which can be used when revegetating areas, or in horticulture.

Organic matter can improve the soil but there can be a risk of introducing weed seeds in the mulch material. Organic mulches are more effective on annual herbs than perennial weeds that can grow through the organic material.

Fire is a major control method for woody weeds in western regions of NSW. It can also be useful for controlling other plants if the conditions are suitable. Fire can be more cost effective than herbicide or mechanical methods. Follow up with other methods is often required.

Spot fires or controlled burns can be used to manage weeds. A controlled burn:

• minimises damage to the environment
• avoids damage to property and livestock
• helps restore land to an open condition suitable for pasture
• creates access for further weed control.

When using fire, ensure all relevant permits are obtained.

Liquefied petroleum gas or propane is used in flame weeders. The weeds do not need to be burnt. The flame ruptures the plant’s cell membranes by raising its water content to temperatures above 100°C. Small seedlings are generally more susceptible to flaming. Upright plants with thin leaves are more sensitive than low growing plants. Flaming has been used for weed control on organic farms and general weed control on hard surfaces in urban areas, e.g. footpaths.

The combination of heat and water pressure breaks down the cellular structure of the weeds. Field trials have shown that steaming kills annual weeds in 24 hours. The foliage from some perennial plants also dies within 24 hours. However, perennial plants can regrow within one or two weeks. Councils have trialed the equipment with mixed results.

Land management strategies that help to reduce weed problems include:

• maintaining dense pastures or desirable ground covers
• reducing soil disturbance and tillage
• reducing nutrient run-off
• managing livestock and grazing to reduce and not spread weeds
• early weed identification
• good weed hygiene.

Grazing and pasture management

Vigorous pastures can outcompete weeds. Improve pastures by adding fertilisers and lime according to soil test results. Some pasture plants are more competitive than others. Seek advice from agronomists for the best pasture plants for your property. Weeds establish more easily in overgrazed pastures. Manage stocking rates to prevent overgrazing.

Goats

Goats browse and eat the foliage, bark, stems and flowers of many weeds. They eat a variety of weeds that sheep and cattle avoid, such as blackberry, sweet briar, scotch broom, thistles, Paterson’s curse and horehound. The nutritional value of these species can be quite high.

Goats can be integrated with sheep, cattle and cropping enterprises to provide weed control and pasture improvement. They can be used for medium to long term weed control. Goats are also useful in inaccessible areas where conventional control methods are not possible.

Reafforestation

Reafforestation is suitable over large areas where other forms of weed control are uneconomic or impractical. Mature trees compete for moisture, nutrients and sunlight and can restrict weed establishment and growth. It can take 5 to 10 years before trees form a dense canopy. During this establishment phase other methods of weed control are needed. A competitive, desirable, shade-tolerant grass or legume can assist with weed control.

Reafforestation includes planting native species and plantation forests. Regularly check sites because some weeds can grow in dense shade. Initial costs of reafforestation can be very expensive.

Herbicides are available as liquids, gels, granules, dissolvable tablets and capsules. The following issues need to be considered when choosing the best application method:

• what is permitted on the labels and any relevant permits
• whether the weed is growing in water or on land
• site type e.g. are the weeds in pastures, roadsides or forests
• the size of the infestation
• size and growth stage of the weeds
• proximity to waterways and other sensitive areas
• access
• the available resources and personal preferences.