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4. A pesticide dose as a concentration in water - the spray mix/water volume rate to apply, is not known.

Examples of pesticide dose

Use this method to adjust your knapsack sprayer when the pesticide label states the pesticide dose as a concentration in water. For example 2% concentration in water; 50 g in 100 L of water; 20 ml in 100 L of water; 2 kg in 100 L of water; 1 L in 100 L of water, but:

  • does not give a water volume or where
  • the spray mix volume rate is given only as a maximum amount to apply to an area e.g. "Do not apply more than 1,000 L/ha".

Note any advice given on the type of spray drop cover that you need e.g. 'ensure good spray coverage'.

Before you start

To calibrate your sprayer for your current spraying task you will need to know:

  • the size of the treatment area
  • the type and size of nozzle (e.g. 03 Blue, 02E, 01 Pink) that you will be using.

Choose a smaller nozzle size that is designed for use with knapsack sprayers. Fit this nozzle onto your knapsack sprayer.

You many need to change the size of nozzle if you find when calibrating that:

  • the spray drops are too small
  • the water volume rate is too large (and there are too many spray drops)
  • the water volume is too small (and there are too few spray drops).

Check your nozzle

Check that your nozzle is in good condition. If your nozzle is damaged or worn then the spray pattern will be poor and you will either:

  • spray too much pesticide which may damage your crop
  • spray too little pesticide and fail to control the pest.

View the video resources to see how to fit a nozzle.

Adjust your knapsack sprayer

Adjust your knapsack sprayer to produce the right spread of spray drops. To do this you need to balance:

  • the nozzle type and size
  • the spraying distance
  • the nozzle spacing
  • the nozzle spraying pressure
  • the spraying speed.
Spraying distance

This is the distance of the nozzle from the target surface: nozzle charts often state this as 50 cm. It can be lower if a more narrow swath is needed.

Nozzle spacing

For a single nozzle, this is the distance between the midpoint of one spray width and the midpoint of the next spray width. On a miniboom it is the distance between adjacent nozzles mounted on the miniboom.

Note the nozzle spacing on your manufacturer's chart. Where there is an even spread of drops across the spray width, then the nozzle spacing, the spray width and swath width are all the same. This means that if you are broadcast spraying or spraying a vertical row laterally, each spray width will need to abut its neighbor. However, if you are broadcast spraying or spraying a vertical row laterally using a standard flat fan nozzle, you will need to overlap the outer edges of the spray widths as there are fewer spray drops at these margins. The nozzle spacing and the swath width will be the same and will be narrower than the spray width.

Spraying pressure

Adjust your pressure regulator if you have one. Use just enough pressure to produce the spray cover and size of drops you want. Pump slower for lower pressures and bigger drops. Pump faster for higher pressures and smaller drops.

Spraying speed

This is the speed at which the nozzle moves over the target surface.

Adjust your spraying speed so that you get the right cover of spray on the target surface with just one pass of the nozzle. Practice spraying with water until you get an even coverage on every leaf with no run off. Visit spraying downwards, laterally or upwards for more help on how to spray.

If changes to your spraying pressure and spraying speed do not give the right cover of spray drops, change the size of the nozzle. Remember to check the nozzle spacings of the new nozzle.

When you can spray an even coverage on every leaf with no run off, move on to the next step.

Find the amount of spray mix: Spraying an area measured in square meters or hectares, downwards

To find the amount of spray mix you will need for this spraying task:

  1. Mark the water level in your knapsack sprayer.
  2. Mark out a test area in the treatment area. Use a 25 m2 test are if spraying less than one hectare. Use a 50 m2 test area if spraying more than 1 hectare.
  3. Spray your test area of crop with water to get a good cover of drops, with no run off.
  4. Mark the new water level in your knapsack sprayer. Calculate the difference to find how much water was used.
  5. Work out how much spray mix you will need for this spraying task. This calculator will help.

Find the amount of spray mix: Spraying a length of crop row

To find the amount of spray mix you will need for this spraying task:

  1. Mark the water level in your knapsack sprayer.
  2. Spray 25 metres of crop row with water to get a good cover of drops, with no run off. If spraying a vertical row laterally/upwards, spray both sides of the row;
  3. Mark the new water level in your knapsack sprayer. Calculate the difference.
  4. Work out how much spray mix you will need for this spraying task. This calculator will help.

Find the amount of spray mix: Spraying several plant, one plant at a time

  1. Mark the water level in your knapsack sprayer;
  2. Spray one plant to get a good cover of drops, with no run-off;
  3. Mark the new water level in your knapsack sprayer. Calculate the difference.
  4. Work out how much spray mix you will need for this spraying task. This calculator will help.

Find the amount of spray mix: Spot spraying weeds

  1. spray water into a measuring jug in the same short bursts
  2. count how many bursts of spray it takes to spray 1 liter of water
  3. look at the plants or weeds to be treated. Assess the number of spray bursts that will be needed to treat these plants or weeds
  4. work out how much spray mix you will need for this spraying task.

 

This calculator will help.

 

Spray mix calculator inputs

To use the spray mix calculator, you will need to know:

  • the number of litres of spray mix that you will need for this spraying task
  • your usable sprayer tank size
  • your pesticide dose as a concentration in water.

The results will show, for this spraying task:

  • the amount of pesticide product (ml, L, g, kg)
  • the amount of water (L)
  • the number of full knapsack sprayer loads
  • any part load
  • the amount of water (L) to add to each knapsack sprayer part or full load
  • the amount of pesticide (ml, L, g, kg) to add to each part or full load.

Spray mix calculator: Dose as a concentration in water

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