Mixing Pesticides

Mixing CPPs for crop protection applications correctly and accurately is essential. If a too low concentration of CPP is used, the crop will not be protected effectively. On the other hand, if the concentration is too high, it can result in overdosing on animals and damaging the crop. A financial loss is unavoidable!

Mixing CPPs does not only involve measuring correct quantities and combining the ingredients. The person responsible for the mixing must be aware of the nature of the CPPs that are being handled, the safety requirements for working with such CPPs, the appropriate equipment that is required, and the correct mixing procedure.

Mixtures are normally mixed immediately before application and should not be stored in mixed form. It is therefore essential that the person responsible for mixing the CPPs has all the required CPPs, equipment and information available to complete the task without delay.

Safe-Handling Of Chemicals

It is essential that the person responsible for mixing chemicals has a thorough understanding of the nature of the chemicals that will be handled, especially with regard to the toxicity of the chemicals, to ensure that the correct safety precautions are taken.

Colour codes, symbols and pictograms are used on the product labels of all chemicals to indicate their toxicity and the manner in which they should be handled.

Colour Codes

Colour codes are used to indicate the hazard classification of the chemical. All agricultural chemicals are classified in terms of their toxicity. This information is displayed on the product’s label and informs the user of the potential hazard l if not used in the correct manner.

The above table indicates the terminology used in classifying chemicals according to their potential hazards. This means that chemicals in Group Ia and Ib will be lethal when a very small quantity is swallowed. A much larger quantity of the substance in Group IV is necessary to be lethal.

Symbols

Pictograms

Pictograms are used to indicate the storage requirements for the product, the type of product, the requirements for protective gear and clothing, and the danger that the product holds for animals.

Mixing Requirements

Apart from the chemicals, the following items are required during the mixing process:

• Protective clothing.
• Measuring equipment.
• Mixing equipment.

Clean water and a bar of soap must also be readily available in case a person’s skin is contaminated with chemical spillage. A person must also wash up after handling the chemicals.

Protective Clothing

The following protective clothing is always worn when handling and mixing chemicals:

• Rubber gloves.
• Cotton overall.
• Rubber boots (gumboots).
• Plastic apron.
• Eye protection (goggles).

If it is indicated on the product label, a facemask or respirator must be used.

Measuring Equipment

To measure the correct quantity of a liquid chemical, an assize-measuring container is required. To measure wettable powders or granules, a scale weighing accurately is needed

Electronic scales generally allow for more accurate measurements, but hand scales can also be used. It is however essential that scales are serviced and calibrated regularly. Scales must be zeroed carefully before the chemicals are weighed.

Calculating the Number of Chemicals or CPPs Required

The example provided for calculating the quantity of pesticide required is based on a tree crop. The standard practice for tree crops is that recommendations for the concentration of crop protection CPPs to be made in millilitres (ml) or grams (g) per 100ℓ of water. This is also the manner in which it is shown on the crop protection program.

The person responsible for mixing the spraying material needs to have a thorough understanding of this notation. Below are a few examples of notations:

To mix the above spraying materials, one has to calculate the quantities of the various ingredients depending on the total quantity of spraying material required. The amount of water is normally used as a basis, i.e. if 500ℓ of spraying material is required, 500ℓ of clean water will form the basis of the calculation. Using the examples above, calculating will be as follows:

Mixing Procedure

The mixing procedures for different pesticides differ. In some cases, it may be required that the compounds are pre-mixed in a separate container. In general, the procedure is to fill the spray tank halfway. The measured pesticide is added (the measuring equipment used can also be rinsed in the tank) and the tank is then filled to the correct level. Stir thoroughly. The pesticide label will specify the procedures to be followed. Read these carefully and apply these procedures. As an example for a mist blower, the following steps are taken:

1. Measure the chemical ingredients accurately, using the appropriate equipment (assize measuring container for liquids and weighing scale for powders or granules).
2. Add the chemical ingredients to a 10ℓ bucket of clean water.
3. Mix thoroughly.
4. Fill the spray tank half with water.
5. Add the 10ℓ mixture to the spray tank on the mist blower and mix.
6. Add the remainder of the water to the spray tank, stirring the mixture continuously.