There are few subjects in UK agriculture that have aroused as much suspicion as the spraying of pesticides. Popularly characterised as "highly toxic", pesticides have struggled to gain acceptance in the minds of the public despite the fact that all have been exhaustively tested and are often less hazardous than many of the chemicals that we consume in our daily diet. In this article we look at application in practice.

There are four main sorts of pesticide that are used in the UK. These are; fungicides that control disease, herbicides that control weeds, insecticides that kill insect pests and growth regulators that prevent plants becoming too tall. When used sensibly in the farming system they provide us with healthy and affordable food and help maintain biodiversity (lots of wildlife) by allowing us to use less land to supply the food we need.

All pesticides must be kept, by law, in a secure locked container or shed that will contain a spill in the event of an accident. In addition all pesticides are classified under COSHH (control of substances hazardous to health) and given a hazard rating which is clearly displayed on the can along with comprehensive instructions for the operator. When handling pesticides, operators wear protective clothing as a matter of course even if the pesticide has no hazard rating and is technically harmless.

The "mixer hopper" allows the pesticide to be added safely to the spray tank where it is diluted many times with water. Later the cans are washed out using the centrally positioned T piece which ensures that all the concentrated pesticide is removed from the can and only applied to the crop.

Pesticides are extremely expensive and are only sprayed for good reason. In this image an intense broad leaved weed burden is threatening a young cereal crop and a selective herbicide (weed killer) will be used. In applying the herbicide the farmer will adjust the application rate so that the weeds are checked while the crop continues to grow. In a few weeks time the crop will start to dominate the weeds which will eventually be smothered and die off.

Most pesticides are applied by a sprayer mounted on the back of a tractor which drives through a field using the tramlines to ensure accurate application. Good practice states that the operator will spray the body of the field first before going round the outer edge last. This minimises the risk of pesticide being transferred to the tractor wheels and transferred elsewhere.

It is important to keep pesticides in perspective. This modern pesticide has no hazard rating under COSHH, is technically harmless and is sprayed at just 20 grams per hectare. Scientific advances are also beginning to allow selective applications, Global Positioning Systems and sensors on the sprayer "read" where weeds and diseases are present and spray only when necessary.

Spraying can only take place when the conditions are good and the crop is at the right stage of growth. In practice this means there should be a light breeze without rain. Very hot weather and very still conditions are unsuitable and all spraying must be done in accordance with the specific instructions of the pesticide. The operator will always log the details of each application recording weather conditions, the amount of pesticide and water used as well as the time of the operation.

Sprayers have controllable sections on their booms which permit areas of the crop not to be sprayed. This is important where the crop adjoins a watercourse or some other conservation feature. In this instance a herbicide is not being applied to the outer edge of the crop so that annual weeds will continue to grow in the crop. This is the creation of a conservation headland.

The modern sprayer is electronically controlled and with regular calibration very accurate. In practice this allows the spray being applied to "run out" just before the work in the field is actually finished. This ensures that the operator does not have to double spray a part of the field to get rid of the last few litres in the tank which would be both costly and wasteful. After the spray has been applied the operator fills up the sprayer with clean water, spraying out the washings onto the crop in the field that he has just sprayed.

Operators are supplied with protective clothing in the event that they have to get out of the tractor to check the sprayer. However, most sprayers also provide a separate tank that contains a large resevoir of clean water that can be used to wash hands or protective clothing prior to getting back into the tractor cab.

When the operator has finished washing out the sprayer he can use clean water from a fresh water tank to wash off the booms in the field. This ensures that any pesticide residue that has caught on the booms remains in the field in which its use was intended.

The application of pesticides is covered by codes of good practice and statutory obligations which are some of the most stringent in the world. Adherence to these regulations makes sense from the point of view of both safety and economy and is a prerequisite for membership to marketing assurance schemes.

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