Knapsack Know-How

Get a handle on knapsacks

Just as for larger applicators, when using hand held sprayers, correct applicator selection and maintenance, along with operator training are all crucial to ensure applications are undertaken efficiently and legally.

Operator training

All operators must have achieved an appropriate certificate of competence in the use of pesticides.

For those using hand-held applicators PA1 and a PA6 qualification is required. Operators should check they have completed the correct units from the PA6 suite for the applicator being used, eg stem injectors.

Testing and maintenance

Hand-held applicators are exempt from the Sustainable Use Directive (SUD) testing requirements. However, all hand-held equipment must be inspected regularly for condition and a record of checks and maintenance kept. A useful checklist is available here

The National Register of Sprayer Operators (NRoSO)  have also produced a useful video in which you can follow the simple steps for pre-use checks.

Measuring and filling

Essential to best practice, is knowing how to measure the correct product and add it to the knapsack. In this video, NRoSO carefully explain the steps to follow and how to deal with minor spillages. Always follow best practice and product label guidelines.

Using a knapsack

The changeable nozzle on knapsack sprayers provides the flexibility to achieve flow rates (litres/min), spray patterns and qualities to apply a wide range of products.

All knapsack sprayers should have some form of built-in pressure regulation, to ensure a constant liquid flow rate. This constant pressure will help ensure the application rate and spray quality required on the product label is achieved. However, for the professional operator repeating the walking speed used in the calibration exercise is critical to achieving consistent target application rates.

Correctly calibrating applicators is a requirement under the Code of Practice for Using Plant Protection Products, which you can find HERE.

Operators must regularly undertake the calibration exercise to check their walking speeds. They should never assume their walking speed, because it can vary according to the surface being sprayed and weight of applicator.

To achieve target application rates throughout treatments the selection of a sprayer with a type and size of pump that minimises operator fatigue will aid consistency. In general, to achieve a given flow rate, diaphragm pump sprayers will require more lever cycles than an equivalent piston pump.

The larger the pump, the fewer pump cycles required to achieve the target flow rate and with less operator fatigue.

To aid your decision making, watch the following video about preparation for calibration.

Knapsack choice

Aim to select a unit that complies with the international standard on backpack sprayers (ISO 19932) to ensure sufficient durability to prevent harmful leaks or spills. Many knapsacks sold in the UK will not meet this standard -particularly those in the DIY market.

Weed control devices

Alternatives to a knapsack sprayer are now available for professional operators to apply certain herbicides, often to specific weeds.

Most of these units are easier to set up than a knapsack sprayer because calibration is minimal and applications are often independent of forward speed. They are especially useful to apply spot treatments of non-selective products to control weeds where any surrounding vegetation is not a target.

Many are also able to deliver applications without drift potential, and some can even apply treatments by closed transfer to the target plants, such as stem injectors or pesticide plugs for the prevention of regrowth from cut stumps. This reduced drift potential is not only beneficial from an environmental perspective, but it can also help reduce the chance of operator contamination.

Nozzle selection

Nozzle choice is an important step in ensuring spraying efficacy.

The NRoSO video below will help you make the right choice when it comes to selecting the correct nozzle for a knapsack spraying device.