mobile feed weather

Spray Distribution

What is water sensitive paper?

Water-sensitive paper before exposure to the spray (2Kb JPEG)
Water-sensitive paper before exposure to the spray

Water-sensitive paper is a rigid paper (card) with a specially coated, yellow surface which will be stained dark blue by aqueous droplets impinging on it. It has been developed for field use for the quick evaluation of low volume (LV) sprays. For droplet assessment aqueous sprays no longer need the addition of dye.

Water-sensitive paper after exposure (courtesy Spraying Systems Co.) (16Kb JPEG)
Water-sensitive paper after exposure (courtesy Spraying Systems Co.)

To Use

  • place the papers in the target area before spraying. Following exposure to the spray the water-sensitive papers will be stained.
  • Retrieve the papers as soon as they have become dry.
  • Check the droplet pattern. For a quick estimate compare the exposed collectors with a known standard or count the droplets either using a hand lens or an automatic image analyzer.

Recommended droplet density in the target area

Low Volume Aqueous Spraying

Numbers of droplets per cm2

Types of Spray

20 - 30


20 - 30

Herbicides pre-emergence

30 – 40

Contact herbicides pre-emergence

50 - 70


To create a droplet counting aid for use with a few drops:

  • Measure accurately and draw a 1cm sq*, square
  • Cut out the centre of the square to create a 1cm sq window
  • Place the window at random on the water-sensitive paper and count the droplets with the lens"

Create a window 0.5cm sq rectangle for use when there are many drops
Create a window 0.25cm sq for use when ther are a great number of drops

*1cm sq = 0.155 sq in

If you would like a leaflet which contains a template for a droplet counting aid, then please contact us with your postal address and we will send you one.