Reasons why product dose, spray mix rate and drop size can vary

Learn why a range of product doses and spray mix/water volume rates can be given on the label. Review our examples which show options for setting up your knapsack sprayer to deliver a chosen spray mix/water volume rate and drop size.

Definitions and label statements

The product dose rate is the amount of formulated pesticide to be evenly applied over the spray area. The pesticide label will often state this as a volume or weight of product for an area of land or crop e.g. 4 L/ha or 2 kg/ha. As the quantities of product are relatively small and the areas relatively large, the pesticide has to be mixed with water to form a spray mix. This gives a volume of liquid that can be safely and effectively applied by a sprayer. The pesticide label states this volume as a spray mix or water volume rate e.g. 200 – 400 L/ha.

Your pesticide label could advise a drop size to use. This may be for reasons of safety: larger drop sizes tend to drift less. Or it might be for reasons of efficacy: contact pesticides can need larger spray mix volumes applied in smaller drops to get the best spray cover.

Most pesticide products are used to control a wide range of pest species in a wide range of situations. For example HALLMARK ZEON® is registered in the United Kingdom to control over 20 different insects and can be used in over 20 different crops. This range of uses makes it necessary to state on the label a range of pesticide doses, spray mix/water volume rates and drop sizes. You need to choose those that are optimal for your intended use.

Factors that may cause product dose, spray mix/water volume rate and drop size to be varied

Product dose rate

Higher product dose rates may be needed to control larger/older pests: lower product dose rates might be used to control younger/smaller pests. Higher product dose rates may be needed to control one species of pest whereas another species may be controlled at a lower product dose rate.

Spray mix/water volume rates

Higher spray mix volume rates can provide a better cover of drops when plants have many leaves and you are spraying a pest that is concealed low down or deep within a crop's canopy. Higher volume rates may also be used when spraying contact pesticides and you need enough drops to fall upon or close to every individual pest.

Drop size: Larger drops may be advised for spraying broad leaved weeds in a cereal crop. This is because these drop sizes are better at reaching and remaining on the flat leaves of the weeds below the crop’s canopy.

Smaller drops may be advised for spraying cereal fungicides and grass weeds. This is because these drops move more laterally and better stick to the crop or weed vertical leaves.

Larger drop sizes can be advised to lower the risk of drift or risk of inhalation by operators.

For each spraying task you will need to decide which type and size of nozzle, at what pressure, will deliver the spray mix volume rate and drop size that you need to produce the right cover of spray drops safely.

Examples of using different nozzle types, sizes and pressures to spray different types of pesticide

To broadcast spray a soil applied product at a spray mix/water volume rate of 140 L/ha: Consider using three low drift flat fan nozzles of 015 size (green) at 1.5 bar pressure to emit 0.42 L /minute. Spray at a height of 50 cm to produce a 1.5 metre swath at a speed of 1 metre/second to apply your spray mix at 140 L/ha.

To spray a band of spray mix that is 20 cm wide at a spray mix/water volume rate of 267 L/ha: Consider using an even flat fan nozzle of 01 size [orange] at 2.0 bar pressure to emit 0.32 L/minute. Spray at a height of 12 cm to produce a 20 cm swath and at a speed of 1 m/second to apply your spray mix at 267 L/ha.

To spray a systemic selective herbicide at a spray mix/water volume rate of 163 L/ha: Consider using a low drift flat fan nozzle of 015 size [green] at 2.0 bar pressure to emit 0.49 L/minute. Spray at a height of 50 cm to produce a 50 cm swath and at a speed of 1 m/second to apply your spray mix at 163 L/ha.

To spray a contact selective herbicide at a spray mix/water volume rate of 243 L/ha: Consider using standard flat fan nozzle of 02 size [yellow] at 2.5 bars pressure to emit 0.73 L/minute. Spray at a height of 50 cm to produce a 50 cm swath and at a speed of 1 m/second to apply your spray mix at 243 L/ha.

To spray a non selective herbicide at a spray mix/water volume rate of 200 L/ha: Consider using a deflector nozzle at 1.0 bar pressure to emit 1.2 L/min. Spray at a height of 50 cm to apply a 1.0 metre swath and a speed of 1 m/second to apply your spray mix at 200 L/ha.

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