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How to use a backpack sprayer?

Backpack sprayer
Written by Frank Schoenmakers | Last update: 04-12-2020

A backpack sprayer is often used in horticulture to spray smaller surfaces and hard-to-reach places. Using the right amount of water and agent is important for an optimal result. In this article, our specialist explains how to use a backpack sprayer and how to calculate the right amount of spray liquid. 



The operation of a backpack sprayer

Most backpack sprayers feature a pressure vessel. This provides constant pressure, ensuring the liquid is sprayed evenly. Some backpack sprayers are equipped with a pressure gauge on the valve, which indicates the spray pressure. A constant pressure is important for a uniform spray pattern. 


Choosing a nozzle

You can mount a nozzle on the spray lance of a backpack sprayer. There are different types of nozzles, each of which is suitable for a different application. It is important to choose the right nozzle to obtain the best possible result.


Calculate amount of spray liquid

There are two methods to calculate the right amount of spray liquid of a backpack sprayer:
1. Dosage according to directions on the label.
2. Dosage according to a solution concentration.


Dosage according to the label when using a backpack sprayer

This is particularly suitable for spraying on the ground or on low crops. 


Step 1 - Calculate the amount of water and agent for the surface area to be sprayed
Example: you want to spray a part of the crop with a backpack sprayer. This is 150 x 3 meters. The surface area is 450 m². The label indicates 5 liters of agent per hectare with 200 liters of water.

So for this area, you need: 
  • Water: (450:10,000) x 200 = 9 L
  • Agent: (450:10,000) x 5 = 0.225 L = 225 ml


Step 2 - Determine the nozzle release
The cap release is the amount of spray liquid the nozzle releases per minute at a certain pressure. You can find it in the nozzle table. 


Step 3 - Determine the spray width
The spray width is the number of centimeters of which the agent hits 100% of the sprayable surface. After all, more spray liquid ends up right below the nozzle than on the sides. That is why you must overlap, so that the same amount of spray liquid is dosed throughout. The entire width the nozzle covers is called the operating width.

backpack sprayer

In order to see the spray width of a nozzle, it is best to spray on a paved area, such as on the concrete path. 

Note: make sure you always keep the nozzle about 50 centimeters above the ground. This not only works pleasantly, but also provides the best result. 

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Step 4 - Determine the walking speed when spraying with a backpack sprayer

The nozzle you use has a spray width of 1 m and an operating width of 50 cm. The first and last 50 cm require a half dosage. So in total, you walk 3 times (namely at 50 cm, at 100 cm and at 150 cm). In total, you walk 300 m in 6 minutes. This means your walking speed is as follows:
  • 300:6 = 50 m/minute
  • 50 x 60 minutes = 3 km/hour
  • For a 100-meter distance, you walk 100:50 m/min = 2 minutes
It is important to constantly walk at the same speed and not stand still when spraying with a backpack sprayer. This way, the spray liquid is distributed evenly and you prevent overdosing. 


Dosage according to solution concentration

Dosage according to a solution concentration is usually applied in tall crops. You must determine the required amount of spray liquid by feel and then dose as indicated on the label. 

Example: if you use a backpack sprayer and you want to spray a part of the crop. This is 150 x 3 meters. The surface area is 450 m². The label indicates 5 liters of agent per hectare with 200 liters of water. Then for this area, you need (450:10,000) x 200 = 9 L water.

With a solution concentration of 2%, you calculate the amount of agent as follows: 0.02 x 9 L = 0.18 L = 180 ml.


Overdosing

A higher dosage of spray liquid does not mean the agent works better; in some cases, it is even counter-productive, especially with the use of systemic agents against weeds. In that case, the above-ground part of the weeds quickly burns and dies with overdosing. This means the agent cannot be absorbed in time and the roots are not reached. As a result, the roots survive and grow back.


Safety measures when using a backpack sprayer

To prevent you from coming into contact with the spray liquid, you can take the following safety measures when using a backpack sprayer:
  • Always wear personal protective equipment while spraying. Note: also wear the right protection while creating the spray liquid!
  • Walk backward instead of forward. This way, you do not have to walk through the mist and will not come into contact with the sprayed crops. 
  • Use a (longer) lance instead of a spray gun that is attached to the backpack sprayer.


Checking and cleaning nozzles

Using nozzles results in wear. This affects the spray pattern. Therefore, you should check nozzles for wear regularly and clean them to avoid wear as much as possible. 


Cleaning backpack sprayer

It is important to always clean a backpack sprayer after use. This is how:
1. Fill the tank with water and shake carefully. Optionally add some household ammonia or chlorine bleach (note: never add both, because this leads to gas formation).
2. Spray the remainder over the crop. 
3. Clean the backpack sprayer externally with water and a brush. Make sure you collect this water, because it may not be discharged as it contains crop protection agents. 


More information about how to use a backpack sprayer.

Do you have any questions about how to use a backpack sprayer, or would you like advice? Then contact one of our specialists, or ask your question using the form below. We'll respond within 24 hours on working days.

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Frank Schoenmakers Schoenmakers About Frank Schoenmakers
With over 30 years of experience, having been a mechanisation product specialist, Frank Schoenmakers has gained significant experience within the horticulture sector. Over the past years he has specialised in spraying techniques. How he feels About that himself? "The great thing about my job is that I can use my knowledge to help growers to improve their cultivation. The reciprocal appreciation is quite valuable."





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