Crop weeds: reduce weed seed numbers in the soil

Page last updated: Wednesday, 17 February 2021 - 10:44am

Please note: This content may be out of date and is currently under review.

One method of weed control is to remove weed seeds in the fallow, stubble and pre-sowing phase. This can be achieved by encouraging the germination of weed seeds and then subsequently killing seedlings or destroying seeds and reducing seed viability. This section covers the different methods used to deplete weeds.

Different weed control methods

Burning crop residues

Burning can reduce the surface seed banks of many weeds. All crop residues (canola, wheat, lupin and others) can produce a sufficiently heated burn to kill weed seeds. A narrow windrow will burn at a higher temperature and improve weed seed kill.

Encouraging insect predation of seed

Weed seeds provide a major component of many insect diets (predominantly ants). There are methods to increase populations of insects over the summer/autumn fallow and therefore increase insect consumption of seeds.

Inversion ploughing

Fully inverting the soil will ensure that weed seeds that were on or just below the soil surface are placed at a depth from which they cannot germinate. This can be practiced every 8-10 years, with conservation tillage used in the intervening years. In Western Australia, annual ryegrass seeds failed to establish and eventually died when soil was fully inverted to a depth of greater than 20 centimetres (cm) using a specialist mouldboard plough fitted with skimmers. This single soil inversion event reduced annual ryegrass numbers by over 95% at Katanning and Beverley for a period of two years.

Autumn tickle

This does not destroy seeds but rather buries them to a depth of 1-2cm, enhancing seed germination by increasing contact with soil moisture. This encourages weed seeds to germinate earlier. A delay between the tickle and seeding is necessary to give an opportunity for the weeds to germinate and then be killed using a knockdown herbicide. The delay to seeding will result in a yield penalty for some crops.

Delaying sowing

This allows greater germination of weeds in particularly weedy paddocks, which can then be killed using a knockdown herbicide or cultivation prior to crop sowing. The longer the delay in sowing, the more weeds germinate and the higher the kill. However, a yield penalty is experienced when sowing is delayed.


Contact information