Pesticides Part 1

Muhammed Alhassan

A Pesticide is any substance or mixture of substances used to kill, repel, or control certain forms of plant or animal life that are considered to be pests.

A Pesticide is any substance or mixture of substances used to kill, repel, or control certain forms of plant or animal life that are considered to be pests. Though often misunderstood or referred to an insecticide, pesticides cover a wide range of substances including:

  1. Herbicide for controlling weed or unwanted vegetation (To read more on how to control weeds, read our article on Weeds and Weeds Control)
  2. Insecticides for controlling a wide variety on of insects
  3. Fungicides used to prevent the growth of molds and fungi
  4. Disinfectants used for preventing the spread of bacteria
  5. Rodenticides used for controlling mice and rat

What are Pests?

Pests are living organisms that are present where they are not desired or that cause damage to crops or humans or other animals. Examples include insects, unwanted plants (weeds), fungi, bacteria, mice and other animals.

HISTORY OF PESTICIDE USE

The pest outbreaks in agriculture have caused severe economic and human losses over time. The potato blight epidemic in Ireland during 1845 and 1846 caused the death of more than a million people. ‘Downey’ and ‘Powdery’ mildew in 1872 devastated the French wine industry.
Despite the advancement in agricultural sciences, insect pests, diseases, weeds, and birds cause-specific crop losses varying between 10 and 90%, and on average 35 – 40% of all potential food and fiber crops are lost to pests.
The discovery of the Bordeaux mixture in 1882 and Paris Green in 1870, proved successful against grape disease and potato beetle, respectively, and heralded the first documented use of pesticides. Sulphuric acid was used as a selective herbicide in cereals in France in 1931 and in the United Kingdom, the same practice was adopted in 1932.

Developments in the use of pesticides

Tobacco juice (nicotine) was one of the first insecticides of the modern era, while the use of arsenic and sulphur can be traced back to Antiquity. However, chemical control only developed in the 19th century, with the use of products of vegetable origin (rotenone and pyrethrum) or mineral origin (copper and arsenic). In 1939, P. Muller discovered the properties of DDT (dichlorodiphenyltrichloroethane), which was marketed in 1943, started the era of synthetic pesticides.
In Europe and in North America, herbicides represent 70 to 80% of the products used (in particular because of the strong increase in maize crops) whereas, in the tropics, 50% of products applied are insecticides. Crop diversification, bringing about improved standards of living in some countries, also changes this balance, and China has also converted the equivalent of the surface of England from paddy fields to market garden crops, resulting in the diversification of products used.

Though pesticides are not yield-enhancing chemicals like fertilizers, they reduce the damage caused by insect pests, diseases, and weeds. It is estimated that each dollar invested in pesticide control gives a benefit of approximately $4 in crop saved, and overall losses to pest would increase by 10% if no pesticides were used at all and specific crop losses would range from zero to nearly 100%[3]

Effect of Pesticide usage

The success of pesticides in reducing damage on crops has become a major source of problems associated with pesticide use. Growers have been so impressed by the spectacular initial reduction of damage on crops and the gain in production per hectare that, they have tried to use increasing amounts of products, thus wasting their resources while contaminating the underground water and the soil. Other problems include spraying apparatus which is often badly maintained, presence of chemical substances damaging to health, safety advice which can be difficult for farmers to understand or are simply ignored. This has resulted in the following consequences;

  • Environmental pollution from the soil and water.
  • Serious health issues for both farmers and consumers because of incorrect use;

Environmental effects of pesticide usage

Pesticides are toxic chemicals designed to be deliberately released into the environment. Although each pesticide is meant to kill a certain pest, a very large percentage of pesticides reach a destination other than their target. They enter the air, water, sediments, and even end up in our food. Pesticides easily contaminate the air, soil, and water.
Soil contamination: Many of the chemicals used in pesticides are persistent soil contaminants, whose impact may endure for decades and adversely affect soil conservation. Pesticides do not necessarily distinguish between “pests” and other living things. The use of pesticides decreases the general biodiversity in the soil. Pesticides can kill beneficial soil bacteria, earthworms, snails, frogs, birds, and other valuable species. Soil microorganisms play a key role in the maintenance of soil structure, transformation, and mineralization of organic matter, making nutrients available for plants. The application of pesticides (especially long-term) can cause significant irreversible changes in their population. The inhibition of species, which provide key processes, can have a significant impact on the function of the whole terrestrial ecosystem.
Water contamination: Pesticides can get into the water via drift during pesticide spraying, by runoff from the treated area, leaching through the soil. In some cases, pesticides can be applied directly onto water surfaces e.g. for control of mosquitoes. Water contamination depends mainly on the nature of pesticides, soil properties, weather conditions, landscape, and also on the distance from an application site to a water source. Rapid transport to groundwater may be caused by heavy rainfall shortly after the application of the pesticide to wet soils.
Fish and other aquatic life may be harmed by pesticide-contaminated water. The application of herbicides to bodies of water can cause plants to die, diminishing the water’s oxygen and suffocating the fish. This can lead to reduced populations, decreased immunity to disease, etc.
Air contamination: During and after the application of a pesticide either in powder form or liquid form, a substantial fraction of the dosage applied may enter the atmosphere in the gas phase and as small droplets and may be transported over shorter and longer distances[5]
Residues arising from these depositions following volatilization, spray drift, air movement can lead to an environmental contaminant.

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References

[1]Anonymous. A practical Guide to Sulphuric Acid Spraying in Agriculture; National Sulphuric Acid Association Ltd U.K. undated
[2] Courtesy: https://pip.coleacp.org
[3]Pimentel, D.; Acquay.H.; Biltonen, M.; Rice.P Silva.M et.al.Environment and Economic costs of pesticide use.bioscience 1992, 42 (10), 750 -760.
[4] U.S. Environmental Protection Agency (2007), Sources of common contaminants and their health effects. Epa.gov. Retrieved on 2007-10-10.
[5] Gath, B., Jaeschke, W., Kubiak, R., Ricker, R., Schmider, F. and Zietz, E.(1993). Depositionsmonitoring von Pflanzenschutzmitteln: Teil 2 SüddeutscherRaum. Nachrichtenbl.DeutscherPflschtzd., 45, 134-143.

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Muhammed Alhassan