Providing practical information to help you protect your farm from biosecurity risks

Weed control

May 1, 2013

Patersons curseWeed control is a year round requirement for successful and profitable livestock, crop, forestry or pasture production. If control measures are not undertaken early, weeds have the potential to become a major problem on your property.

Weeds can lower crop yields and pasture quality by competing for soil moisture, nutrients, space and light; they can harbour pests and diseases and many are toxic to livestock.

Weeds can enter your property in a variety of ways:


  • New or returning livestock can carry seeds in their stomach contents or on their skin or coat.
  • Vehicles can carry seeds though the soil or mud on wheels or undercarriages.
  • Equipment that has not been adequately cleaned may carry weed seeds in dirt or other matter.
  • Wild or feral birds and animals can carry seeds in their stomachs and also on their skin or coat.
  • Visitors, staff, family or seasonal workers can pick up seeds on their clothing or in mud on their boots and clothing.
  •  Inadvertently introduced thinking it is a garden plant becasue some weeds are very attractive.

You should aim to reduce weed numbers and keep them low with an ongoing control program.  Tools you might use in your management program include:

Ongoing surveillance
Check your property regularly and implement a control program, especially if the weeds are toxic to livestock or have the potential to take over useful pasture or crop fields.

Crop rotation
Alternate cereal and broadleaf pasture or crops. Broadleaf weeds are easier to control in cereal crops, and grassy weeds are more easily and cheaply controlled chemically in broadleaf crops.

Making hay or silage from crops or pasture prior to seed set reduces the weed seed bank and possible spread of weed seeds. Cutting must be done early enough to ensure that viable seeds are not included in the hay or silage.

Pasture management
Techniques such as pasture topping by mowing or using herbicides, strategic heavy grazing or burning can all have a role in weed control programs. Cleaning grasses out of legume pastures in winter is a common practice. This involves spraying grasses such as barley grass and vulpia out of pastures in winter to stop seed set, improve nitrogen build-up and reduce root diseases in subsequent cereal crops.

Agronomic practices
Practices such as using weed-free seed (preferably registered or certified) and sowing on time with optimal plant population densities and adequate nutrition contribute to weed control. Some crops and varieties are more competitive against weeds than others.

Timely cultivation
Some producers use varying combinations of mechanical and chemical weed control to manage their fallows or stubbles. Using knockdown herbicides instead of cultivation for fallow commencement, as well as pre-planting in the autumn, can provide weed control while protecting the soil structure.

In-crop weed control
A wide range of pre-emergent and early post-emergent herbicides are available for in-crop weed control. The stage of growth of the weed and the crop are vital factors to consider when planning the successful use of post-emergent herbicides.

Herbicide resistance in weeds is a problem that is becoming more widespread through Australia, so bear this in mind when deciding on the best options for your property. Herbicide resistance can be managed by having a good crop and pasture rotation, by rotating herbicide groups and by combining both chemical and non-chemical methods of weed control.

Early detection and reporting enhances the chance of effective weed control or eradication. Any unusual weeds should be reported immediately via the Exotic Plant Pest Hotline on 1800 084 881.