A Brief History of Agricultural Pest Control

Almost as long as agriculture has been in existence, humans have used pesticides in one form or another to protect their crops from insects and diseases.

The ancient Sumerians used sulphur to control insects and mites, the Chinese used arsenic and mercury and the ancient Romans used salt to control weeds.

However, the majority of agricultural pest control was through crop rotation, tillage and the variation of sowing times.

It was after World War II that the use of chemical pesticides really took off. The insect-killing capabilities of DDT had been discovered in 1939 by Paul Muller, who received the Nobel Prize for his efforts, and after the war ended, DDT became the insecticide of choice for farmers everywhere.

By 1975, organochlorines such as DDT were replaced by organophosphates and carbamates. These work by deactivating a particular enzyme vital for nerve function in many insects.

While organochlorines were phased out because of their dangerous accumulation in food chains and interference with reproductive processes, organophosphates were soon discovered to have their own drawbacks. Although they degrade faster than organochlorines, they also possess greater acute toxicity and pose a serious health risk to those exposed to large amounts over long periods (i.e. pesticide applicators).

So pyrethrin compounds began to replace organophosphates, to the point where they are now the dominant insecticide used. Pyrethrins kill insects by interfering with the flow of sodium in their nerve cells. They are considered to be the safest insecticide because they are biodegradable and break down rapidly in air and sunlight.

In the last few decades, new pesticides were developed which are less harmful to animals and humans and don’t accumulate in the environment. These include juvenile hormone mimics, which prevent larval stages from becoming adult insects, avermectins, which are produced naturally by micro-organisms in the soil and baccilus thuringiensis toxins, which destroy the wall of an insect’s gut.

The first widely used herbicide was developed in the late 1940’s. Known as 2,4-D, it was cheap and easy to make and killed most weeds, while leaving grasses largely unaffected. Today, new herbicides have been developed which are more selective than 2,4-D and break down more quickly after application.

The history of herbicides is less about toxicity to humans and animals as it is about long-term environmental effects through run-off and contamination of ground water.

Today, around four and a half million tons of pesticides are used on our crops every year and that figure is growing exponentially as more third world countries adopt first world agricultural methods.

As long as there are crops, there will be a need for pest control, but the challenge for tomorrow’s growers is to learn from the mistakes of the past, such as DDT, and develop pest control methods that are more selective and cause less damage to the environment.

There are many factors that can contribute to spray drift and environmental contamination. Nozzle wear is common and spray equipment needs to be frequently checked for wear.

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