Concerns About Pesticides

In every population of bacteria or plant weeds, there is a very small population which is immune to the effects of the pesticide. As the affected population is eliminated by the pesticide treatment, the immune portion of the population slowly, year after year, becomes the dominant segment of the pest population. As a result, the farmer must apply more and more pesticide to achieve the same effect, risking greater damage to health and the environment. Eventually, the pesticide becomes ineffective and can lead to the collapse of some agricultural systems with highly resistant pests and no natural enemies left to control them.

Below: Irrigation ditch, a potential highway for pesticides.

Contamination and toxicity

Pesticides can be toxic to the surrounding environment - the plants, fish, animals, certain useful insects such as bees as well as to the natural enemies of the pests. The consequences to these latter species can be particularly dramatic since the devastation of a natural control agent population by pesticide use may result in a resurgence of pest populations.

The danger of toxicity to humans who handle or are closely exposed to pesticides is also important, and a great deal of care must be taken when using pesticides; this also applies to household applications of chemical weed and insect pesticides. Because of the interaction between air, soil and water, a pesticide applied to one medium (i.e. to the soil in a field) can contaminate elsewhere as the material is transported to other locations once mixed with another medium (i.e. rain water that runs off into a river.) Pesticides spread further afield than where they were applied, and the consequences of unanticipated pesticide contamination can be as harmful as they are unexpected.