Pests and Poisons in Agriculture

Pests are organisms that reduce the quality or yield of a crop. Many crop pests include aphids and caterpillars; however slugs and snails also cause a lot of damage. Pest control involves Biological, Chemical and Physical processes.

Plants which are grown closely together may cause the rapid spread of fungal diseases and insect pests, from plant to plant, which soon affects large areas and causes heavy damage in a short period of time. It is important to control unwanted organisms, such as weeds, pests and insects that generate diseases from fungi and viruses, in order to obtain a harvest of high quality.

Biological Pest Control

Biological control does not use any chemicals. It involves other organisms that are predators or parasites of pests. E.g. Greenhouse infested whitefly is where the predatory wasps are introduced. The wasp lays eggs into the scale (larva) of the whitefly. A young wasp emerges from each larva, having used the larva as a nutrient supply.

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The whitefly young are killed, so its population decreases.

Genetic Engineering can also be used. A gene must be transferred to a potato plant which enables them to produce a natural insecticide. This destroys 50% of aphids that attack the plants. Therefore the amount of damage is reduced.

Advantages of Biological Pest Control

• This method is very specific and will only affect the pest chosen to be eradicated.
• Once the system is introduced, the control of organism establishes itself and does not have to be reintroduced.
• Pests do not become resistant to biological control.
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• There are no concerns about damaging the environment.
• It needs fewer applications and therefore can often be cheaper than chemical control.

Disadvantages of Biological Pest Control

• There is often a certain amount of time difference until introducing the control organism to significantly lower the number of pests. This process is relatively slow.
• The biological control programme usually keeps the number of pest at a low level; it rarely eliminates the pests completely.
• The control organism may become a pest in its own right. E.g. Aphids are controlled by ladybird beetles.
• Chemical Pest Control

Pests and weeds can be controlled with Chemical Pesticides. Pesticides are sprayed onto the crops to kill the pests. These chemicals kill Insecticides, which are used to fight insect pests. Fungicides, which target the fungi and causes many plant diseases. Herbicides are the ones that kill weeds.

Most of the insecticides now applied are synthetic compounds that affect the nervous system of insects when come in contact. The most effective include DDT (dichlorodiphenyltrichloroethane), chlordane and toxaphene. The organophosphate insecticides are Malathion, Parathion and Dimethoate.

Among the most effective herbicides are the compounds of 2, 4-D

(2,4 Dichlorophenoxyacetic Acid) where only a few kilograms of which are required per hectare to kill broad leaved weeds while leaving the crop plants unaffected.

DDT

DDT is a colourless chemical pesticide, applied to eliminate crop eating insects. It was first used in World War II to combat yellow fever, typhus, elephantiasis and other insect related diseases.

In India, DDT reduced malaria from 75 million cases to fewer than

5 million in a decade. Crops sprayed with DDT doubled their yields.

Publications in 1962 from an American marine biologist named Rachel Carson suspected that DDT caused reproductive dysfunctions mainly in animals higher in the food chain and thin egg shells in birds. Some insects gradually developed DDT- resistant strains whose populations grew.

In other cases wasps were being eliminated from the spraying. In 1973 DDT was banned in U.S. except for extreme health emergencies or only accessible under strict control.

Structural formula of DDT

There are several chemical substances involved in the production of different pesticides. These include

Contact Pesticides

These are pesticides sprayed directly onto the crop. Contact insecticides are usually absorbed by the insect through the tiny gas exchange pores known as the spiracles. Contact herbicides and fungicides are absorbed directly through the surface. These may be low in cost but need to be reapplied as the effect of the chemical is temporarily and moreover some pests are able to avoid the pesticide.

Systemic Pesticides

Systemic insecticides are sprayed onto the crops. They are absorbed by the leaves and transported around the plant. A sap sucking insect such as an aphid feeding on the crop plant will be poisoned when takes in the pesticide. This method can be very effective as the spray doesn't need to come in contact with every other insect. Systemic herbicides are absorbed by the leaves and transported through the weed and kill all of its tissues including the roots.

Residual Pesticides

These are sprayed onto the soil or used to treat the seeds before they are planted. They remain active in the soil and kill fungal spores, insect eggs and larvae.

Advantages of Chemical Pest Control

• This process is cost effective as farm chemicals are an economical way of controlling pests. They require low labour input and allow large areas to be treated quickly and efficiently.
• A suitable farm chemical is available for most pest problems with variations in activity, selectivity and persistence. The best product can be chosen for this situation. This allows more flexibility in management options and better timeliness of pest control.
• Chemicals certify quality and quantity. They ensure a plentiful supply and variety of high quality and wholesome food. The modern society demands nutritious food free from harmful organisms.
• Farm chemicals frequently prevent pest problems. E.g. Preventing weeds in gardens and lawns.
• If no chemicals were available to control the environmental pests, our environment would suffer. The use of herbicides to control crop weeds reduces the need for cultivation as well as reducing land degradation.

Disadvantages of Chemical Pest Control

• The Non-Target organisms, including the predators and parasites of pests can also be affected by chemicals applications. The reduction of these beneficial organisms can result in changes in the natural biological balances. E.g. Loss of honey bees and other pollinating insects.
• Drift of sprays and vapour during application can cause severe damage and residue problems in crops, livestock and the general environment. Environmental pollution from this careless system can cause harm to the wildlife.
• Residues in food for humans and livestock can be a consequence of direct application of a chemical to the source of food, by the presence of pollutants in the environment.
• Ground water contamination by leached chemicals can occur in high use areas if persistent products are used.
• Resistance to the pesticide can develop in target pests due to overuse and incorrect use of chemical.

The Ideal Chemical Pesticide

• The chemical pesticide must be specific and should only exterminate the concerned pest and must not cause any harm to other living organisms. This includes humans, birds, mammals and the beneficial organisms such as the natural predators of the pest. E.g. Earthworms and honey bees.
• It should be chemically stable and biodegradable. Must not be reapplied to the crop plants. Once applied, it should immediately have dominant effect on the controlling of pests.
• It needs to be cost effective. Testing and developing of a new pesticide can be very expensive. The manufactures must keep in mind that the new pesticide only remains useful for a limited time as the pests tend to create genetic resistance against the pesticide, therefore the pesticide becomes ineffective.

Maximum Benefits From Chemical Pesticides

To maximise the advantages and benefits of chemical pesticides while minimising the potential problems, this can be achieved by...

• Ensuring there are adequate safeguards over the manufacture and use of these products.
• Making sure that the chemicals are only used with an integrated pest management.
• Ensuring that the chemicals are applied correctly, safely and accurately by well trained and competent applicators.

Conclusion

In my opinion, I think that controls such as biological, chemical, physical are very important when it comes to keeping our environment safe. However, the strength of chemical pesticide is far greater than any other method and I believe that by means of improving this technique of extermination, chemical pesticide can become the ultimate line of attack when it comes to eradicating organisms which damage the environment. There are different approaches which are vital to reduce or even eliminate the majority of pests, insects and other organisms which cause harm to the crops in the environment. When selecting a good quality of Chemical Pesticide, there are some considerations involved...

• Selecting the appropriate product. The one which can significantly lower the quantity of pests and cause limited damage to the crops.
• The product needs to be compatible with other controls used aside, e.g. (biological control) It should not disrupt or interfere with other controls.
• The application should be aimed to the target organism and must be accurate in its performance.
• The application should be favourable to all weather conditions.
• The product must only be applied once to the crops and immediate protection and extermination should be maintained.

The different ways which are carried out to control the pests all have their advantages and disadvantages. By the correct, safe and accurate methods pest control can be minimised and farming will become more profitable.