The Issues Associated With Pest Control.

The Issues Associated With Pest Control

The two main types of pest control are biological and chemical control, and there are different types of these, each of which has issues associated with them.

Chemical pesticides can be split into three categories: insecticides, herbicides and fungicides. Each of these combat different types of pests: insects, weeds and disease causing fungi. There are three types of pesticides which work in different ways to eliminate pests and increase the yield of the crops.

Contact pesticides are sprayed directly onto crops. They are absorbed by insects through spiracles, which are gas exchange pores, and are absorbed by weeds and fungi through their surfaces. The pests are poisoned and therefore cannot compete with or destroy the crop plants. Contact pesticides are relatively cheap, but their effects are short lived and they have to be applied regularly. This method is not completely effective; however, because spraying of the crops does not guarantee that each pest is poisoned and killed therefore the plants can still be destroyed.

Systemic pesticides are also sprayed onto crops, but work differently to contact pesticides. They are absorbed by the crop, and transported around the plant. Sap sucking insects such as aphids will feed on the plant, and take in the pesticide and will be killed. Weeds will also absorb the pesticide and it will work by killing all its plant tissues, including underground roots. This type of pest control is very effective because it is not necessary for each insect to be sprayed, and it is also selective, therefore the crop plant will not be damaged and nor will other insects who pose no threat.

Residual pesticides are sprayed onto the soil or the crop seeds before planting. They remain active in the soil killing fungal pores, insect eggs and larvae and weed seedlings. These are effective in that many pests are prevented from becoming a problem, but once the plant has grown, any insect eggs which are laid on the plant will not necessarily be killed unless the plants are sprayed with another type of pesticide.

The two main issues associated with the use of chemical pesticides are economic and environmental. Chemical pesticides are very expensive to develop because they have to be extensively ...

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The two main issues associated with the use of chemical pesticides are economic and environmental. Chemical pesticides are very expensive to develop because they have to be extensively tested before being used widely. It needs to be specific and not damage any organisms that do not affect the crop plants. They also need to be chemically stable, yet biodegradable so that they do not decompose before application, yet will be broken down easily in the soil to harmless substances. Pesticide developers must spend money ensuring that their product will be effective, but they also need to make sure that these costs will be covered by sales.

Increased use of pesticides can result in the development of resistance. Genetic mutations in pests can mean that specific pesticides no longer work; therefore new ones must be developed. This results in more costs for manufacturers, which can be covered by sales, but the process must begin again as the pests become resistant once again.

Environmentally, pesticides can be very damaging. If they are not specific, they can wipe out populations of organisms which were natural predators of the pests, and can result in plants not being pollinated because of eradication of insects which would do this. If a pesticide is persistent, it does not degrade quickly and easily to harmless substances, but will continue to harm other organisms which it has an effect on. An example of a persistent pesticide is Agent Orange, 2,4,5-T. This was used in the Vietnam War by the Americans, who sprayed it onto the Vietnamese rainforests to reduce the cover it gave. It produces dioxin which is toxic and caused birth defects to the children of many men who were in contact with it during the war. It has also been found that other pesticides can act as carcinogens and increase the risk of cancer in the people that are in contact with them. Persistent pesticides can also cause bioaccumulation. This is the build up of the pesticide in organisms through food chains. For example, DDT, a persistent pesticide, has been found in large concentrations is birds of prey. This is because small birds eat many insects which have eaten many pests which have been sprayed with DDT. The birds of prey will eat many small birds, each of which will contain a fairly large concentration of DDT. This can then prove fatal for the bird of prey, and can lead to a decrease in fertility, and sometimes can almost wipe out populations. Many pesticides which have been found to have highly dangerous effects have been banned from use in some countries, especially if they have been found dangerous to humans.

Biological control uses other organisms such as predators or parasites of the pest to control them. There are none of the environmental issues of chemical control associated with biological control because each pest is preyed on by one specific predator which does not affect any other organism. Toxic chemicals are not involved; therefore bioaccumulation is not a problem. Persistence is also eradicated, because as the pest numbers decrease, the prey decreases and therefore the population of predators will decrease. In most cases of biological control, the pest cannot become resistant to the method of control, but in cases where viruses are used it is possible. For example, the myxomatosis virus is used to control rabbits as pests, but some rabbits now have genetic resistance to the virus and therefore it does not work as effectively.

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