module 11
Grazing management
Objectives
At the end of this module, you will:
- understand role of grazing animals in introducing and controlling weeds
- understand how plants respond to grazing
- appreciate that different grazing animals can be used to target different weed species
- appreciate the importance of timing and intensity
of grazing to achieve the desired result
Module Outline
- Introduction
- The importance of grazing management
- Use of grazing animals in cropping systems
- Summary
- References and further reading
Introduction
Pastures are subject to frequent disturbance from external influences, which can all profoundly disturb the ecological balance. Such disturbances can include:
- grazing by livestock
- actions of insects and plant pathogens
- applications of fertilisers and herbicides
- cutting or burning plant material
If not carefully controlled, this ecological balance can be readily shifted to favour weed species (see Module 5).
The importance of grazing management
Grazing management can be a useful tool for the management of weeds in pastures. However, the use of grazing for weed control is poorly implemented in Australia. There are a number of reasons for this and these are outlined in the following reading.
This reading also discusses how grazing management can be used to create a desirable pasture composition. You should particularly note the sections describing the use of mob stocking and variation in grazing pressure to reduce the incidence of undesirable plant species in pastures. Appropriate use of grazing pressure can contribute considerably to management of weeds in pastures. You should also note the difficulties associated with maintaining the appropriate number of stock to effectively vary grazing pressure at the correct time.
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Use of grazing animals in cropping systems
The above reading only considers the use of grazing animals in perennial pasture systems. However, stock are also used for the control of weeds in cropping systems. The reading below by Popay and Field (1996) briefly discuss this issue. Across much of southern Australia, stock (particularly sheep) are used to clean up crop fields after harvest. The stock are placed in fields to consume spilt grain, weed seeds, and any remaining weeds. This practice is also valuable in that it spells pastures during early summer when many annual pasture species are setting seed.
However, stock will also trample weed seed into the soil, providing better conditions for germination in the ensuing season. Stock can also be used to reduce weed seed set in pasture in the year before a crop is sown. Many crop growers who practice continuous cropping have gone away from animals totally. Therefore, the use of grazing animals for weed management in cropping systems is declining.
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More recently, the possibility of re-introducing grazing animals to remove annual ryegrass from crops has been suggested. Penfold and Miyan (1996) have suggested that certain crops such as faba beans, coriander, chickpeas, and mustard are generally unpalatable to sheep. At low stocking rates, sheep will prefer to eat annual ryegrass rather than the crop.
Stock are frequently used in other parts of the world to graze weeds in orchards; however, this is not a common practice in Australia. Growers are concerned by the possibility of damage from grazing animals to high value products. The use of grazing in the integrated management of weeds in cropping systems will be considered in more detail in Module 17.
Summary
Grazing animals offer an opportunity to control certain types of weeds. In pastures, grazing animals become a major method of weed control, but they are used more sparingly in cropping systems. Different grazing animals have different preferences for plant species. This allows the use of more than one species to successfully manage a large number of weed species.
However, it is uncommon to see more than one species of grazing animal being used to control weeds within a field. To be truly effective for weed management, the timing and intensity of grazing needs to be controlled such that the weeds are grazed hard, but bare patches do not appear in the pasture. One way that this can be achieved in practice is by the use of movable fences that confine stock to a small area. Proper grazing management of pastures requires frequent monitoring and adjustment of grazing intensity.
It is rare for grazing animals alone to be used successfully for long-term management of weeds. Frequently intervention in the form of herbicides, mowing, burning, re-sowing, or other methods is required to re-dress the balance to obtain a competitive pasture. The integration of these methods for successful pasture management will be discussed in Module 17B.
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References and further reading
Allan, CJ, Holst, PJ & Campbell, MH 1993, ‘The development of grazing systems for the control of weeds by integrating goats with cattle and sheep’, Bulletin of Department of Agriculture, New South Wales.
Beattie, AS 1993, ‘Grazing for pasturemanagement in the high rainfall, perennial pasture zone of Australia’, in DR Kemp, & DL Michalk (eds) Pasture Management Technology for the 21st Century, CSIRO, Canberra, Australia, pp. 62-70.
Campbell, MH 1997, ‘Control of Hypericum perforatum L. (St. John’s wort) by grazing management’, Plant Protection Quarterly, vol. 12, pp. 97-99.
Fitzgerald, RD & Lodge, GM (eds) 1997, ‘Grazing management of temperate pastures: Literature reviews and grazing guidelines for major species’, Technical Bulletin 47, NSW Agriculture, Orange, Australia.
Holst, PJ & Allan, CJ 1996, ‘Targeted grazing of thistles using sheep and goats’, Plant Protection Quarterly, vol. 11, pp. 271-273.
Kemp, DR & Michalk, DL (eds) 1993, Pasture management: Technology for the 21st Century, CSIRO, Canberra, Australia.
Lodge, GM & Whalley, RBD 1985, ‘The manipulation of species composition of natural pastures by grazing management on the Northern Slopes of New South Wales’, Australian Rangelend Journal, vol. 7, pp. 6-16.
Medd, RW, Kemp, DR, & Auld, BA 1987, ‘Management of weeds in perennial pastures’, in JL Wheeler, CJ Pearson, & GE Robards, (eds), in Temperate Pastures: Their production, use and management, CSIRO, Canberra, Australia, pp. 253- 261.
Mitchell, RB & Abernathy, RJ 1993, ‘Integrated management of California thistle in pasture’, Proceedings of the 46th New Zealand Plant Protection Conference, pp. 278-281.
Penfold, CM & Miyan, MS 1996, ‘IWMA - integrated weed management alternatives’, Proceedings of the 11th Australian Weeds Conference, pp. 73-75.
Popay, I & Field, R 1996, ‘Grazing animals as weed control agents’ Weed Technology, vol. 10, pp. 217-231
Watkin, BR & Clements, RJ 1978, ‘The effects of grazing animals on pastures’ in JR Wilson (ed.), Plant Relations in Pastures, CSIRO, Canberra, Australia, pp. 273-289.
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Self assessmentDo you know:
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