Mixing pesticides safely

You will need your:

• container of pesticide and label; your
• knapsack sprayer that has been checked, calibrated and is ready for use;
• clean water;
• a mixing tray;
• a pesticide box; your
• planning notes;
• measuring cylinders or jugs;
• a spill kit of a dust pan and brush, sand or soil and a plastic bag or appropriate container that can be labelled and securely sealed: and

the personal protective equipment that should be worn when mixing that product and as directed by your pesticide label.

You will know from the product label and your local expert:

• the amount of product to be applied; and
• the water volume rate to use.

In this demonstration we will be spraying at the label rate of

• 4 L of pesticide in
• 200 L of water; to be sprayed over
• 1 ha (10,000 square metres) of land. Although we will be spraying a much smaller area of 1200 square metres.

To spray 1200 metres we will need 24 L of spray solution containing 0.48 L or 480 ml of pesticide (you may find our online spray mix calculator will help you with your own calculations).

The capacity of your knapsack sprayer’s tank is important here. Filling your sprayer up to the top will increase the risk of leaks from the filler cap and its vent. To reduce the risk, International Standards recommend a minimum 5% unused tank volume so that there is a gap between the top of the spray liquid and the tank opening. We will allow a 10% spare volume and so suggest filling this sprayer to the 18 L mark at the maximum.

This means we will need one tank of 18 litres containing 360ml of pesticide in 17.64 litres of water;

and a part tank of 6 litres containing 120 ml of pesticide in 5.88 litres of water.

Choose your mixing site carefully; make sure that you will not have to carry a loaded knapsack sprayer very far. If you do not have a dedicated mixing area or need to mix your spray solution nearer to the treatment area, refer to your label for any advice on selecting a suitable mixing site.

Ideally it should be away from animals, children and surface water such as streams and ponds and not near any drinking water sources or habitation and other sensitive areas. The ground must be flat and your mixing tray stable.

Before you start mixing make sure that the weather and other conditions remain suitable for spraying. If you are not sure what to check, view our video ‘Just before you spray’ for some suggestions.

Pesticides are more safely transported from your pesticide store to field mixing sites in a lockable non-permeable box. These boxes will also keep your pesticide much more secure when you are spraying.

It is best to add pesticide and water from the side furthest from the straps on the sprayer. Straps can absorb drops and spills of liquids so it is safer when you are pouring from this side. We will mix the 18 L quantity first.

Remove the sprayer’s lid and place this upside down on the mixing tray.

Using clean water and with the filter basket in place, add about 9 litres of water carefully and without splashes

Pesticide quantities for knapsack spraying use are likely to be small so make sure you use equipment that can accurately measure small amounts of product. Sometimes graduated container caps can be used. Measure out the exact amount of liquid pesticide that you need for 18 L - 360 ml of this product for this use. Use caution and take great care with all undiluted chemicals that you are handling; PPE will help to protect you but it’s much better – for you and the PPE – not to come into contact with the pesticide at all.

Pour in the product onto the water in the half full tank.

For safety, replace the pesticide container cap now.

Using clean water, rinse the measuring cylinder or jug and pour the rinsing water into the tank. Do this three times. Replace the lid.

Carefully agitate the pesticide with the water until it is fully dispersed by raising the sprayer a few centimetres by its handles or its straps and gently rocking it back and forth.

Remove the lid, and taking care to avoid spills and drips, place it upside down again onto the mixing tray. Add the remaining water up to the tank scale’s 18 litre mark. Replace the lid and agitate the spray solution now …….and again later when you are about to use it.

If any accidental spill occurs then use the sand or sawdust in your spill kit to contain the liquid and absorb it. Do this as soon as possible and before it spreads too far, contaminates other surfaces or – if on the ground - penetrates below its surface.

Scoop up the contaminated material and place it in the plastic bag that is then sealed and labelled for safe disposal later.

Return the pesticide container to its store or secure box and lock it. Re-check the label to see what additional PPE you need for the way you are applying that product and then go spraying!

Our operator is following Best Practices so will retain the use of his coveralls, gloves, boots and face shield for downward spraying this product.

It is very good practice to make up a little less spray solution than is needed for your last knapsack sprayer load. This means you will leave a small unsprayed area which you can later spray with the water used for cleaning your sprayer. So when you come to mix the part tank, mix less than is needed.

In this case we had calculated to use a further 6 litres in total, so we will prepare 5.5 litres of pesticide solution. We should then have a small unsprayed area that will be later sprayed with the cleaning water.

Put about half of the total volume of water required into the tank. In this case we need 5.5 litres, so put 2.5 litres of water in to start with.

Measure and add the product needed. In this example, we will measure out 110 ml to make up 5.5 litres of spray solution. Rinse the measuring cylinder 3 times, and add this water to the spray liquid.

If you have emptied any pesticide containers, also rinse them with water and add the rinsing water into the sprayer tank. Do this twice more (3 times in total).

Replace the tank lid.

Agitate the sprayer to mix the product with the water’ Add the remaining water so that there is now 5.5 litres of mixed spray solution and agitate the tank again now … and then again just before using.

Check that all pesticide container lids have been replaced securely and place the containers in your lockable pesticide box.

Spray out this part load and place a cane where you now have an unsprayed small area.

Put your clean mixing equipment away ready for the next use. Have a look at our video on cleaning your knapsack sprayer for advice on using the cleaning water to spray the remaining area.