The use of synthetic pesticides can prevent pests and disease from attacking a valuable crop, which is needed for food by the general population. They can also make production easier for the farmer, thereby allowing increased production with minimal effort or input of time.
Disadvantages
Despite the benefits, pesticides can have devastating effects on the environment. What pesticide are in reality is a poison, used to control a particular pest or disease. Unfortunately, pesticides can often harm more than their intended victim. One of the first times that this was documented was in the book Silent Spring by Rachel Carson. In this book she documented how the spraying of DDT, a pesticide which was later made illegal in the United States but is still used in other countries such as Mexico) killed their intended insect victim, but also other creatures, such as birds which ate the bugs. The result is a poison which travels up the food chain. Compounding the negative effects is a process called bioaccumulation. Using DDT as an example, animals have difficulty removing DDT from their systems. When a bird eats an insect with DDT on it, it keeps in its system all of the DDT which was in the bug, as well as all of the bugs that it eats. When a cat eats that bird, it accumulates in its system all of the DDT in the bird, thereby accumulating all of the DDT from all of the bugs. If a dog were to eat the cat, than the dog would accumulate all of the DDT in the cat, which ate so many birds, which all ate so many bugs. What we have discovered is that as you move up the food chain, the concentration of DDT (or other substances, such as mercury) increases. These are ramifications which travel up the food chain, which have unknowable and potentially devastating effects. (note: DDT is not the only chemical which is known to bio-accumulate. Along with mercury, there are several different chemicals, each with differing side-effects, which are known to bio-accumulate)
Because synthetic pesticides are a relatively new convention, we don’t know what their effects on the environment are. The current policy in the US is to allow production until it is proven unsafe, and as of right now there are several thousand different chemicals, which are untested, and yet are available on the market.