Firstly, we need to establish the core concept of a pesticide. A pesticide is a group of different chemicals that are specific to kill different types of animal or plant. The three most common types of pesticide are insecticides, fungicides and herbicides.
“Pesticides are a chemical or chemicals sprayed onto plants to kill insects and grubs (1)”.
Causes & Effects of Insects
If we were to live in a society without pesticides, what would happen? Insects would eat all of the crops, we use to feed our world population. The insects would eat all photosynthetic material causing low photosynthesis, causing low growth, stunted specimens and a low yield. They would eat all vegetables and fruit, lay eggs in crops, which would cause low consumer confidence due to illness.
This intern would facilitate losses of huge profit, jobs and also the economy would suffer. We know from the basic facts of biology that plants needed to be pollinated. With increased use of pesticides, this would not occur, as most insects would be killed, this would not be good, as insects pollinate the vast majority of are crops.
Advantages & Disadvantages of the use of Pesticides
The main reason we use pesticides are to stop inter-specific competition, either between weeds and crops or between insects and crops. This then improves the yield of crops either directly or indirectly, therefore increasing profit. Diseases can spread through one crop in many fields, due to the farmers only planting one crop; this is called a mono-culture. The pests have many plants to attack of the same variety, and so they do not have to adapt. This speeds up the pests as it infests a particular crop. We use pesticides to stop the rapid advancement of the pest through the rest of the crop.
The difference between a chemical pesticide and a biological one is that a chemical pesticide involves toxic chemicals that get in to a pest’s digestive system and cause it to die like a poison.
A classic disadvantages was shown when a chemical pesticide company introduced dichlorodiphenyltrichloroethane in the 1980’s, the common name used for it was DDT (3). This particular chemical attacked the nervous system, causing rapid death, even in low concentrations. It was so popular because it was stable. This means that it did not break down and stayed in the ecosystem for a long time scale, and also killing a wide range of insects, therefore it was labelled hugely economical (4).
DDT was found so effective, it was used liberally in World War 2, to kill the mosquito, a vector for malaria, and in addition, it killed many other invertebrates. As DDT is fat soluble, so it is selectively retained in fatty tissue, it does this instead of circulating animals venous system and excreted via their kidneys. Consequently, DDT accumulates at each stage of the food chain, known as bioaccumulation.
Although this case is an extreme circumstance, laws have now been put in to place to stop these dangerous chemicals from coming on the market again, although there is still a question about the amount of pesticides used on crops.
The Chemical pesticide advantages are, that they are cheap, easy to spread and they will destroy 90% (2) of pests. However, the disadvantages are leaching of soil (2) can spread the pesticides. This then causes eutrophication like most fertilisers. This process occurs when chemicals drain through porous soil into a nearby river system killing fish and other wildlife living in the biome. This causes algae and pond weed to grow covering the river decreasing oxygen and light causing more fish to die. The cycle continues until there has been a complete break down in the food chain or the river is cleaned by environmental agencies.
Another point is that due to the nature of a food web from producer to consumer, a bird will eat several mice a day. The chemical levels will increase in the bird. Then foxes eat these birds, although the toxic levels in the birds are small, the fox eats many of them. This causes a toxic build up in the foxes body, eventually killing it. This process is called bioaccumulation. As you can tell just by adding a small amount of pesticides to a localised area, you can cause a whole food web and ecosystem to be destroyed causing a depletion in large numbers of species. Although this is a localised case, in just one field, imagine if this was done all over the country. This would cause a countrywide drop in population of all animals that are linked by into each other’s food webs as of the case of DDT.
Advantages & Disadvantages of the use of Biological Agents
A biological agent, is a creature that naturally eats a particular animal, plant or fungi, without destroying the primary crop. For example, if there were an outbreak of aphids on a crop, you would add ladybirds to eat the aphids, when all the aphids were gone the ladybirds would either migrate or die.
Nevertheless, the disadvantages to having many living organisms are they have to be bred and packaged in special greenhouses using special methods. This makes it very expensive to use in an open environment such as a field. Although the biological method is widely adopted in the greenhouse market, due to being in a situation which organisms can not fly away and migrate but are kept in a closed system.
The advantages of this particular method is obvious, it stops eutrophication and bioaccumulation. You may well think why do farmers not use this method. However, because of its expense and uncontrollable application, it is a way of keeping numbers of pest down, not eradication of the pests. This is why a mixture of both is one possible technique.
Advantages & Disadvantage of Integrated Systems
The advantages of the integrated system are that it does not cause mass build up of poisons in an ecosystem (bioaccumulation). The soil does not contain as much pesticides and therefore the leaching effect will be greatly reduced which has a direct effect on eutrophication. In addition, fewer weeds become resistant. This is when plants will not die, as a plant will build up immunity to the herbicides sprayed on the fields. Fewer pesticides will not be need, creating a larger profit margin for the farmer. The biological agents such as ladybirds, are then introduced back in to the system keeping the levels of pests down in future years and also introduce species to already dwindling numbers in the wild.
One other type of integrated system is genetically modifying crops so they are less resistant to funguses. On the other hand, to make rapid growing crops so weeds do not have a chance of competition. All of these developments are very new nut with more development sometime in the future pesticides will be seen as a ridiculous way of controlling pests. Although if these developments happened to be cross-bred with weeds, there could be an ecological disaster.
Although the situation has now occurred that farmers need to gain as much profit as possible for farming to be sustainable. There is still a question on when to use each different method, do they add biological agents first to kill most pests then destroy the biological agents with the pesticides. I think the answer is to still use pesticides for most out breaks but introduce the biological agents when safe to do so after chemical pesticides have been used, reducing the amount of pests for the future.