Chemical Control

Herbicides can be extremely beneficial in a serrated tussock integrated weed management plan; however, they should not be relied on as the sole method of control.

Chemical Selection

A number of herbicides are registered for controlling serrated tussock in Australian pastures: glyphosate, flupropanate and 2,2-DPA. Currently glyphosate and flupropanate are used. 

Glyphosate is a non-selective herbicide that kills green, actively growing plants. It is essential to apply glyphosate carefully to minimise non-target damage.

Flupropanate is a slow acting herbicide that is predominantly absorbed through the roots and leaves. It can take between 2-12 months to kill the plant, particularly if affected by drought. 

For more information on chemical selection, click on a title below to expand.

Using a dye marker when spraying can help avoid missing any plants. Source: DEPI Victoria. 



Over spray of glyphosate can lead to bare ground, increasing the risk of re-invasion. Careful application is essential. Source: Luke Pope

Glyphosate is a non-selective herbicide that kills green, actively growing plants. Careful application is essential to minimise non-target damage.

Characteristics of glyphosate include:

• absorbed through the leaves and green stems
• fast acting—kills treated plants one to four weeks after application
• not residual—ceases to work once it contacts the soil
• no withholding period for grazing stock; however, avoid grazing stock for seven days following application to allow absorption into the plant.

Glyphosate is suitable for all land-use situations and can be used in spot spray and broadacre applications. The optimum time for spot spraying serrated tussock with glyphosate is May to October.

Advantages of glyphosate

• Able to target other weeds at the same time when spot spraying.
• A quick method of killing serrated tussock.
• Nil grazing withholding period.
• When applied accurately, is very effective.

Disadvantages of glyphosate

• Unlikely to affect serrated tussock seed bank levels.
• Broadacre treatments of glyphosate can lead to a monoculture of weeds. Replace the tussock with desirable species to prevent this from occurring.
• Glyphosate is non-selective. Over-spray may open up bare areas, increasing the risk of re-invasion, especially in a dry year.

Flupropanate is a slow acting herbicide predominantly absorbed through the roots and also the leaves. It can take 2–12 months to kill the plant, particularly if affected by drought.

Characteristics of flupropanate include:

• A residual action in the soil that prevents or limits the growth of emerging serrated tussock seedlings. Residual life varies depending on soil type and rainfall, but may generally last 2–3 years. Time may be reduced by large rain events or soil movement from flooding. Residual action in soil may allow tolerant desirable pasture species to increase in density, providing good competition for serrated tussock once the residual effect has gone.
• Some selectivity, but may cause non-target damage, particularly to native species
• A long withholding period for grazing animals which may have large implications for grazing management.

Flupropanate is suitable for spot spraying, broadacre spraying and wick wiping applications. The optimum time for spot spraying serrated tussock with flupropanate is during the vegetative stage of growth, generally between March and June.

While there are many introduced and native grass species that are tolerant to flupropanate application, many are not. Using flupropanate, particularly in native pastures, may change its composition. For example, high rates of flupropanate can reduce the levels of weeping grass (Microlaena stipoides) and increase the level of red-leg grass (Bothriochloa macra).

Soil type can alter the effectiveness of flupropanate. Flupropanate can become more active in lighter soils (shale/sandy) than heavy soils (clay). There have also been some instances of serrated tussock showing resistance to flupropanate. More information about herbicide resistance can be found on the Herbicide resistance page. [insert link to herbicide resistance page]

Advantages of flupropanate

• Flupropanate is a residual herbicide and will reduce the growth of serrated tussock seedlings for an extended period—up to a number of years under very low rainfall conditions.
• Tolerant desirable species are able to establish and stabilise an area while the tussock degrades.

Disadvantages of flupropanate

• Residual effects may reduce the growth and establishment of the crop or pasture.
• Long withholding period for broadacre applications may be a deterrent due to grazing management issues.
• Application of high label rates of flupropanate may result in a loss of highly productive desirable pasture species.
• Lactating stock must not graze treated areas. 

Methods of Herbicide Application

Herbicides can be applied to serrated tussock a number of different ways, depending on the size and density of the infestation, the terrain, and the particular chemical used.  

When using herbicides, recording specific information may be required – each state has their own requirements for record keeping.

Herbicide use requires correct timing and application rates to be effective and will vary on the situation and density of serrated tussock. Always carefully read and follow all label, material safety data sheets, and any off-label minor use permits.  

All current label and minor-use permit details for serrated tussock control can be found at the Australian Pesticides and Veterinary Medicines Authority at www.apvma.gov.au

For more information on methods of herbicide application, click on a title below to expand.

 



When spot spraying, take your time to ensure you treat all plants. Source: VSTWP

Herbicides, glyphosate, 2,2-DPA and flupropanate, can be used to spot spray serrated tussock. Individual plants are treated using a knapsack or spray unit with handgun. Spot spraying can be done on foot or on a vehicle. Include in daily farm activities.

When spot spraying:

• only spray the target plant—do not overspray
• spray every serrated tussock plant you find
• monitor where you spray
• use a coloured marker dye
• control scattered infestations first and work back into denser infestations
• spray at optimum times for best results
• spray with a carefully directed spray to avoid over-spray—stand over the plant for a full view
• limit the areas you plan to spot spray—set achievable goals
• take your time and have regular breaks.

Always follow up treatments with further spot spraying or chipping, as some plants may have been missed and new seedlings will always emerge.

Spot spraying is suitable for:

• All situations
• Best in light and scattered infestations; however, excellent results have been obtained from diligent spot spraying of medium to high density infestations, when sufficient resources are available.
• An effective follow up treatment.

Application will vary depending upon the chosen chemical. Each chemical has a different mode of action.

• Glyphosate – cover entire plant with herbicide, but not dripping, and apply when the plant is green and actively growing.
• Flupropanate – apply a small amount of herbicide into the centre of each tussock. This may reduce damage to non-target species.
Take your time to ensure treatment of all plants.

A few tips are:

• look behind to see if any plants have been missed
• work with the sun behind you so that you are not squinting when looking for plants to treat
• use flags, stakes or fence droppers to help you divide up and mark areas being treated. This may be particularly useful when working in gullies or hilly country
• use a tracker, such as a GPS, in conjunction with a spray marker to indicate spray lines.
Always carefully read and follow all label directions and use correctly calibrated equipment.

Advantages of spot spraying

• Possible to target other weeds at the same time.

Disadvantages of spot spraying

• Can be easy to miss plants, particularly small plants hiding under larger ones.
• Can be labour intensive.
• Non-target damage may occur.

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Broadacre spraying can be economical in large scale infestations. Source: DEPI Victoria

Broadacre spraying can be achieved via ground or aerial (helicopter or fixed wing) application. It is important to use the correct herbicide for your situation. Broadacre spraying should not be used in isolation. Know the dominant species within the pasture and their susceptibility to different herbicides. Follow up with competition strategies that focus on enhancing pasture density and ground cover.

Considerations before broadacre spraying

Selectiveness of the herbicide relies on the correct rate of herbicide per hectare being applied in an even and consistent manner across all vegetation. To achieve this, the sprayer needs to be calibrated and driven accurately at a consistent speed. It is important to:

1. Know the type of paddock you will be driving and consider what speed will be appropriate for the entire area – choose one speed and stay constant, unless using a flow controller.
2. Choose appropriate spray nozzles to suit the ground speed and volume of water to be applied per hectare (refer to the herbicide label). Avoid spray drift by using lower pressures and nozzles (such as air induction nozzles) that produce large droplets. For example, coarse to very coarse classification.
3. Clean filters and check the spray pattern and output of all spray nozzles on the spray boom.
4. Use a method of guidance when driving across the paddock to ensure that strips are not missed or double overlapped. For example, foam marker or GPS systems.
5. Use an automatic rate controller; particularly for aerial application. A rate controller may save you money as you may use less chemical and consequently do less damage to your pasture.

Broadacre spraying is suitable for:

• Situations where the density of serrated tussock is too high and extensive to effectively conduct spot treatments.
• Ground application on arable land and aerial application on difficult to access terrain. Also useful when the area affected by serrated tussock is so large it is more cost effective to apply herbicide by air. Correctly calibrate all spray equipment before use, always use clean water and strictly follow all herbicide label directions and rates.

Warning

There have been some disastrous events involving aerial spraying of flupropanate, where all species, including desirable natives were destroyed. If using this option, ensure you use a GPS to mark areas treated and flow control equipment. Exercise extreme care and caution. Do not broadacre spray native pastures with flupropanate, or other areas, that have susceptible native grasses as the dominant pasture species.

Advantages of broadacre spraying

• More economical in large scale infestations.

Disadvantages of broadacre spraying

• Aerial spraying can be very expensive when using high water rates.
• Success rate depends on the skill levels of the pilot if not using a guidance system.
• High risk of non-target damage.



Wick wiping can treat serrated tussock with a low volume of herbicide, but like all methods, follow up monitoring and treatment is required. Source: Malcolm Campbell

Wick wiping is a technique that selectively ‘wipes’ the herbicide onto weeds. Equipment can be mounted onto a vehicle or hand-held, and is applied from a ropewick or rotating carpet wiper saturated with concentrated herbicide.

Only use wick wiping when a distinct height difference occurs between beneficial pasture species and serrated tussock. Always monitor treated areas for small, missed plants and remove by chipping or spot spraying.

Wick wiping is suitable for:

• Removal of large serrated tussock plants in pasture situations.
• Infestations on level ground—wiper height can not be automatically adjusted.

Advantages of wick wiping

• Minimal damage to desirable vegetation.
• Low risk of off target damage.
• Requires small volumes of herbicide.

Disadvantages of wick wiping

• Will only treat large plants and can miss small juvenile plants.
• Can be labour intensive.

Spray topping uses low label rates of herbicide to reduce or prevent seed-set in serrated tussock. This may help in reducing the serrated tussock while doing minimal damage to beneficial species.

It can be used as a broad acre treatment to stop serrated tussock seeding. It will not kill serrated tussock plants, but will affect them so that they do not flower, or if already in flower will not produce viable seed.

However, spray topping will not kill seed once it as already formed on the plant. Always use with other methods of control such as spot spraying, chipping and grazing management.

Spray topping is suitable as a short term option only and particularly in pasture situations with medium to high level infestations of serrated tussock.

The timing for spray topping is critical for this method to be effective. For glyphosate, treat prior to flowering, around mid August to mid October. Always apply herbicide in accordance with label directions.

Advantages of spray topping

• Reduces seeding.
• Less damaging done to desirable pasture

Disadvantages of spray topping

• Does not kill the plant.

 

More detailed information on chemical control can be found in the National Serrated Tussock Best Practice Manual.