What Growers Should Know About Air-Assisted Electrostatic Spraying

Data submitted by leading universities demonstrate that air-assisted electrostatic sprayers:

• Significantly increase insect and disease control.
• Reduce the amount of agrichemical applied.
• Cut the application water used by half.
• Reduce waste and off-target drift by over 50%

What is Air-Assisted Electrostatic Spraying?

Air-assisted electrostatic sprayers manufactured by ESS produce spray droplets which are 900 times smaller than those produced by conventional sprayers. These tiny droplets are carried deep into the plant canopy in a high-speed air-stream.

The result is more than twice the deposition efïciency of both hydraulic and non-electrostatic airassisted sprayers. Electrical charging causes a natural force of attraction between the spray droplets and the plant, similar to the attraction between items of clothing created by the tumbling of a clothes dryer.

The charge on the droplets is small, but the force pulling the spray towards the plant is up to 75 times greater than the force of gravity. Droplets literally reverse direction and move upwards, against gravity, when passing a leaf surface.
This remarkable phenomenon by which the spray coats the undersides of the leaves and the backsides of the stems is known as electrostatic wraparound. Spray coverage is the uniformity of spray droplets on plant surfaces. Figure 3 demonstrates leaf coverage using air-assisted electrostatic sprayers with that of hydraulic sprayers.

Electrostatic sprayers achieve greater spray coverage by combining air turbulence with tiny, evenly sized spray droplets. Dense under leaf coverage (Figure 2) results from electrostatic wraparound. The benefïts are clear: insect and disease control are better because the chance of contact is greater (see A New Way to Look at Under Leaf Spray Coverage on page 6).

Chemical burn is reduced because chemicals do not accumulate in large single deposits. Low-volume spraying requires 10 to 25 times less water carrier than standard spraying.

This is possible because of the uniform droplet size and improved coverage characteristics achieved by the electrostatic sprayer.

This is a good example of ESS air assisted electrostatic application of dye, on to the underside of a coffee leaf 400 mm inside and at the bottom of the thick coffee tree canopy. This dye is applied by a side on spray and well illustrates, how the positively charged leaf attracts the negative charged droplets onto its surface. Even when the spray is not directly targeted towards the surface of the leaf and when it is already, protected by the outer canopy of leaves.

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