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Weed control

One reason pastures fail to establish is competition from weeds.

Pastures don't compete well with weeds in their early stages and poor weed control in the lead up to sowing can results in pasture failure.

Weeds are often difficult and expensive to control in both young and established pastures. It is best to reduce the weed population and residual seed banks in the soil through a planned control program prior to sowing. This can take years to achieve and requires careful planning.

Ongoing attention to the length and intensity of grazing, tactical use of fertiliser and chemicals are all key to success with pastures.

Identifying target weeds

Different weeds have differing commercial impacts. It is important to focus on the weeds posing the greatest commercial threat to the enterprise.

The first step is to identify the weeds in the paddock(s) where pasture is to be established and to categorise these as either grasses or broadleaf weeds. Woody weeds may also pose a problem and may require specific control methods. These can also be ranked in order of importance and a program can then be put in place to control them.

Control options

The aim of weed control is to reduce the weed seed load in the soil seed bank to remove the threat of weeds germinating and challenging the new pasture. Weed control should commence well before a new pasture is sown, generally several years. This can be achieved through the use of herbicides and strategic grazing.

Herbicides

Broadleaf weeds or grasses can be controlled using a specifically targeted herbicide for a single species or a knock-down herbicide employed for general control. A range of additives that improve the effectiveness or aid the uptake of herbicides are available. Specialist advice from an agronomist or consultant should be sought when deciding upon the best control option for a particular situation.

Cropping

A cropping program can be useful in reducing weed populations. This allows grasses to be controlled within a broadleaf cropping phase and broadleaf weeds to be controlled in a cereal phase. Several years of cropping with a broadleaf and grass-based crop rotation can be very effective in controlling weeds.

Grazing

Strategic grazing can also be used as an effective weed control method. Spray-grazing is an example of a grazing strategy used to control weeds. When implementing this strategy however, grazing withholding periods must be considered.

Pasture weeds and desirable species are both susceptible to grazing at establishment and reproduction. Managing when, how hard and how long livestock graze on pastures will influence how well desirable species compete with undesirable plants or weeds.

Woody weeds

Woody weeds crowd out pastures by competing for nutrients, water and sunlight. Woody weeds are typically difficult to control and often require a combination of herbicide, mechanical and grazing techniques. Goats can be useful to control some woody weeds in certain circumstances.