Pest control and pesticides

Modern agriculture, compared with earlier systems grows larger amounts of food per hectare.
There are many reasons for this:

• High-yielding varieties of plants and animals;
• Better animal and plant nutrition; and


• Control of competitors for the crops and animals we grow.

Chemicals, in the form of fertilisers, fuels and pesticides, play an ever-increasing role in agriculture.

Why pest control?

Higher yields in agriculture can be achieved by controlling a whole range of pests, such as weeds, insects and diseases. In undisturbed ecosystems, population sizes are kept in check by a variety of predators and diseases; in agricultural systems, where monocultures prevail, these predators are usually absent and certain organisms, whether indigenous or introduced, will be a problem. Unless these pest organisms are controlled, their competitive effects will drastically lower yields.

Why pesticides?

Pesticides have enabled high yields by knocking out a whole range of competitors: weeds, insects, diseases, internal and external parasites and feral animals. Chemical control methods are often used in preference to other methods because they are quick, easy and control can be more certain.

Some land conservation practices depend on chemical control. Minimum tillage practices used to save soil structure and limit soil erosion, rely on the use of herbicides. These herbicides enable the farmer to do away with most cultivation.

Problems with pesticides

In recent times, the associated environmental hazards have become recognised. Certain pesticides are persistent (or non-biodegradable) because they do not break down easily. Such pesticides pose problems, because they can build up in organisms throughout a food chain and persist in the environment. Organo-chlorines, (such as DDT) break down slowly. Their persistence in the food chain has resulted in their being found in human tissues.

These same pesticides can also pollute the soil by remaining in it for a long period of time. Farmers who used another organo-chlorine, like dieldrin, to control cattle ticks and lice or to control insect pests in potato crops, now find that organo-chloride residuals in the soil are high enough to contaminate the meat of grazing animals.

In a similar way, pesticides can enter streams and rivers with run-off from farmland. For these reasons, persistent organo-chlorines are now banned from use in agriculture. The development of resistance by the pest to a particular pesticide and the killing of non-target organisms are also problems. Strict rules and regulations govern the use of pesticides. In fact, the label on a pesticide container is a legal document. It must be read before use and the materials must be used according to the conditions outlined on the label. Pesticides should only be used if they are going to be sufficiently selective, (that is, kill the target organism only) or there will be damage to the crop or the environment.

What are the alternatives?

Following are a list of alternatives to pesticides:

Environmental control practices

These involve manipulating the environment to make it less attractive to pests and so decrease the severity of infestations. Commonly used environmental control methods for weeds include cultivation, grazing, burning and mulching. Insects may be controlled by improved standards of hygiene and sanitation in sowing, harvesting and a storage of equipment to remove potential breeding areas and sources of food supply. Crop rotation and modification of climatic and soil conditions are used to control disease organisms.

Physical control methods

These include such practices as vermin proofing of grain storage facilities, trapping of pests, fencing, screening and the installation of stainless steel mesh for termite protection in the housing industy.

Biological control methods

These, which are available for a limited number of pests, include the introduction of predators, parasites and diseases, which are host-specific. An alternative is to breed strains of the productive plants and animals, which are resistant to the pest. Companion planting which have natural repelling properties, for example, Pyrethrum Daisy and garlic which have proved to be successful in the home garden.

The advantage of biological control is its host-specific nature and once established, little energy input is required to control a pest. The disadvantages of biological control is that it is a long-term control technique that will not always solve today's pest problem. There is also the prossibility that the introduced agent may in itself become a pest, for example the Queensland Cane Toad.

Quarantine

Quarantine methods include preventing the entry of infestations (controlling movement of hay) or by isolating problems in the field (footrot outbreak on property) and having quarantine control points at airports and state borders.

Integrated pest management

Integrated control programs involve using more than one method to control a particular pest.

An integrated program is likely to be more successful than a single control measure and is environmentally desirable because:

• Less pesticide is used;
• Strategic use of pesticides is more effective; and
• Resistance to pesticides is less likely to be induced.

A program may involve:

• Use of natural predators or parasites to keep a pest in check; for example, Bacillus thuringiensis (a bacterium used as a pesticide) can be used to control caterpillars on horticulture crops;
• Use of genetically-altered organisms to combat the pest; for example the use of sterile male fruit flies;


• Maintenance of biological diversity by growing a variety of crops;


• Maintenance of remnant vegetation to encourage predators;


• Use of resistant strains of crop plants;


• Destruction of pest breeding places;


• Monitoring of the occurrence of pest organisms in crops and herds; and


• Well-timed use of highly specific pesticides when all else fails.

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