Everyone in the world depends on agriculture for food production. Despite improved technology, world food production has barely kept pace with population growth. Crop yields and efficiency of crop production must be increased. This can be achieved by reducing food loss by pesticides. Without some form of pest control, which is a form of controlling organisms, which reduce crop growth and crop yields, crop and animal losses would be severe, so throughout history farmers have used various means of controlling pests.
Since the introduction of pesticides, bio pesticides, cultural control and integrated pest management (IPM), farmers are producing higher crop yields. (8)
Pesticides are chemical substances used by humans to control, destroy, repel or attract pests in order to minimise their detrimental effects. Pests are any organisms (plant or animal) that reduce the yield of a crop. The term pesticide is an all-embracing word for herbicides (kill plants), insecticides (kill insects), fungicides (act on fungi), and so on. Most pesticides are poisons and aim to kill the target species. Pesticide use is mainly associated with agriculture and horticulture. Pesticides are used worldwide and in a wide variety of habitats and are thus a new environmental factor. (1)
Many of the negative environmental effects of agri-food production are associated with chemical use, especially that of pesticides. (2) Pesticides pose one of the greatest dilemmas of our time. The science of pesticides use has become an accepted part of industrial food production systems, relied on to provide the levels of food production. But there is widespread unease among farmers and scientists – about agricultural and public health systems, which are based on the deliberate introduction of toxic products into the food chain and the environment. (3)
The rapid growth in the use of pesticides in agriculture has increased the level of risk for the users of pesticides, the consumers of treated foodstuff, domestic animals and the environment. Thus pesticide use arise a number of ethical, moral and social issues. (2) Pesticides can affect species diversity, food chains and potentially many other aspects of ecosystems. (4) By destroying the pest pesticides may deprive the pest’s natural enemies of their only source of food, resulting in their removal. (5)
Another issue of using pesticides is their effect on nutrient cycling. Pesticides reduce the rates of decomposition and mineralization resulting in the reduction of soil fertility. Herbicides can reduce vegetative cover of the ground, promoting soil erosion via runoff and wind. Pesticides can enter water either from the air or by runoff, where they can have harmful effects on human health and can cause disruption of aquatic ecosystem. (4)
Another major issue with the use of pesticides is the harm they cause on human health. Chemicals like DDT aldrin and dieldrin are toxic to broad spectrum of animals, including humans. (1)
Injury to reproductive systems, birth defects and cancer, are effects that pesticides cause on humans. An estimated 3 million reported cases of pesticide-associated poisoning occur annually, resulting in 220,000 deaths. 99% of these occur in the developing world. (6) Another issue with pesticides is the economic problems, including direct and indirect costs. Using pesticides is very expensive and cost governments a large amount of money. (7)
Although pesticides have certain advantages mainly in killing pests, they have also many disadvantages concerning their effect on wide range of animal species, soil structure, and water quality, and most important, on human health.
Biological control of pests has traditionally meant regulation by natural enemies: predators, parasites and pathogens. As such it represents a form of population management preventing unchecked exponential growth of pests. (1)
Bio pesticides fall into 3 major classes:
Microbial pesticides consist of a micro organism (e.g. bacterium or virus) as the active ‘ingredient’.
Incorporated- Protestants are pesticidal substances that plants produce from genetic material that has been added to the plant.
Biochemical pesticides- they are naturally occurring substances that control pests by non-toxic mechanisms. They include substances such as insect sex pheromones and extracts that attract pests to traps. (9)
Unlike some insecticides, bio controls are often very specific for a particular pest and other helpful animals, or people can go unaffected or disturbed by their use.
However, bio control programs typically cost more. In addition to bio control agent(s), more labour in the areas of scouting is required, compared to applying of a conventional pesticide. A bio control agent is also an introduced species, and many survive without controlling the target pest. Some may even attack non-target organisms. (10)
Cultural control methods such as crop rotation, tillage, mixed cropping, removal of crop residues and sowing times to favour crop or natural enemies rather than pest may also be considered as bio control. Cultural controls employ these methods to make the environment less attractive to pests and less favourable for their survival. (1)
However, cultural controls require long-term planning for greatest effectiveness and they need careful timing. They are more demanding on the farmer’s competence. They may be effective for one pest but may be ineffective against a closely related species. Also cultural controls do not always provide complete economic control of pests. (11)
Integrated pest management (IPM) is pest population management, which combines and integrates biological and chemical controls in a sensitive way. IPC programmes have the twin objectives of economic and ecologically acceptable management of pest populations.
They aim to keep pest populations below the level of economic injury, or even prevent their development, while causing minimum harm and disruption to a crop and especially the beneficial natural enemies of the crop. (1)
However, although it claims to be integrated, IPM still tends to take a linear approach, and it fails to deal with the complex interrelationship between influencing variables.
The implementation of IPM may be too complicated. Also predicting pest and natural enemy population trends is difficult. Because of the complexity of crop systems and the site-specific nature of many pest problems, relying on predetermined static treatment thresholds is problematic. (12)
It is unlikely that chemical pesticides will ever be the final answer to pest control, because quite apart from their effects on the ecosystem, resistant strains are constantly evolving. Pesticides do not offer a long-term, complete solution to pest problems; they kill pests but need to be reapplied periodically, and this cannot continue indefinitely. One possible solution is to put emphasis on biological control and procedures like cultural control and IPM, which make it impossible for the pest to complete its lifecycle and do not cause many moral, ethical and environmental issues. (5)