The most important goal of applying pesticides with a sprayer is to distribute the chemical evenly throughout the foliage of the crop. Insufficient doses may not provide the coverage and control needed. Excessive use is expensive because it wastes pesticides and increases the potential for groundwater contamination.
Two general types of sprayers can be used to spray pesticides in greenhouses: hydraulic and small volume.
There are many variants suitable for specific crops or growing methods. In a hydraulic sprayer, a pump provides energy to deliver the spray material to the target. Water is the carrier and the pump produces 40-1000 psi of pressure. Spray material is usually used "wet" or "drip". A nozzle on a boom or hand-held spray gun breaks the spray into small droplets and directs them to the foliage.
In low volume sprayers, the spray material in a water or oil carrier is injected into a high velocity air stream created by a fan, blower compressor. To obtain adequate coverage, the air within the leaf crown must be replaced with air containing pesticides. Since the droplet size is much smaller, good coverage can be achieved with less chemicals.
One way to differentiate hydraulic sprayers from small volume sprayers is by droplet size. Hydraulic sprayers produce spray droplets with diameters ranging from 200-400 microns. Small volume sprayers produce mist. Small droplets from a mist or mist applicator can result in more even coverage and greater potential for contact with insects or disease. In contrast to hydraulic sprayers, spray materials are often used to "glow" because it is difficult to see individual droplets on the leaves.