Application Technology
Getting the Pesticide from the pack to the pest safely and economically.The basic requirement of a pest control application is that it delivers the pesticide to the sites where the active compound will destroy the target pest. This is mostly achieved by applying the spray to surfaces and/or cracks and crevices
Spray equipment is designed to atomise (break up) the liquid into a large number of small drops and effectively distribute them on the required sites.
To achieve atomisation, the liquid is delivered under pressure to and through a small orifice in a nozzle. The force to pressurise and move the liquid comes from two basic sources:
1. Motorised pump, often referred to as a power sprayer, or
2. Pneumatic pressure gained by pumping air into a container, which in turn forces the liquid out of the container when the outlet is opened.
The device used to create the droplets is called a nozzle. The most commonly used nozzles in urban pest control are hydraulic nozzles.
There are two common types of hydraulic nozzles used in the urban pest control industry:
(1) A hollow cone nozzle in which the pressurised liquid passes through angular holes, rotates in a swirl chamber, and as it emerges through a control orifice, forms a conical diverging sheet which breaks into droplets.
(2) Fan nozzles produce droplets by the break-up of a flat fan-shaped sheet of liquid formed as the liquid passes through the orifice.
There are many variations in design of these two groups of nozzles which allow the technician to select the most appropriate for a particular task.
In general, the combination of pressure and nozzle orifice will determine the volume applied and the droplet size produced. The greater the pressure the higher the volume and the smaller the droplets.
The smaller the orifice, the lower the volume and the smaller the droplet size.
The technician then, by a combination of pressure and nozzle selection is able to quite markedly and effectively predetermine the volume of application and the coverage achieved.
Droplet size is becoming a more important consideration for many technicians, as droplet size is the major determinate of spray drift and economic coverage.
Droplet size (droplet diameter) is measured in microns (um). One micron (1um) equals one millionth of a metre.
| Relation of Droplet Size to Number of Droplets and Total Surface Area of 1cm2 of water | |||
| Type of Application | Droplet Number | Droplet Size (um) | Total Surface Area of Droplets |
| Rain Nozzle | 30 | 4000 | 15cm2 |
| Coarse spray | 30,000 | 400 | 1.5m2 |
| Fine spray | 30,000,000 | 40 | 150m2 |
| Fine aerosol | 30,000,000,000,000 | 0.4 | 15ha |
This is a dramatic illustration of the effect of droplet size on coverage. As rain size droplets, the 1 cubic centimetre of water would cover an area of roughly 3 postage stamps, as a fine aerosol, about 15ha....incredible but true. Fumes, smoke and vapours which have droplet sizes from 0.1 to 0.001 micron, can achieve mind boggling coverage from very small volumes applied.
The relationship between the coverage and volume applied is also important. You can see from the table above that you would need about ten times as much volume using a very coarse spray as compared with a very fine, almost aerosol spray, to cover the same area. Droplet sizes have implication for both effective coverage and economical application.
The other side of the coin with droplet size, is the issue of spray drift. Spray drift is the potential of the droplets formed to travel on the wind after application.
| Distance Droplets Travel in the Time Taken to Fall 3m in a 5km/hr wind | |||
| Type of Application | Droplet Size um | Time for Droplet to Fall 3m (Approx) | Distance (Approx) |
| Coarse spray | 400 | 1.65 seconds | 2.1m |
| Fine spray | 40 | 4.2 minutes | 54m |
| Fine aerosol | 0.4 | 28 hours | 155km |
This table assumes that evaporation of the spray does not occur. However, notwithstanding that, the table demonstrates the huge potential for pesticides particularly, sprayed outside, to move on to neighbouring properties. Thus the desire to improve coverage and to reduce costs by using small droplets must be tempered by the concern of spray drift.
Spray drift is also a concern, particularly for neighbouring properties, during the external treatment of buildings for spiders. From an application point of view, smaller droplets which give better coverage and stick to spiders webs more effectively are ideal, however the associated risk of drift is high.
Two major ways of overcoming this concern for drift is to use extension wands to allow the nozzle to be kept as close as possible to the surface being sprayed, and use nozzle selection to achieve the desired droplet size, instead of pressure. This will minimise both the volume applied and the risk of drift.
The use of high pressures and handgun mounted nozzles which shoot the spray 3 to 5 metres through the air before the spray reaches the target results in high volume use, higher application costs and major drift dangers.