It is important that buying agencies select the type of sprayer that is most appropriate for the intended use. The following notes will assist in the selection process.
For the purposes of these guidelines, RA means a portable sprayer with a spinning atomizer - usually a disc or cup - driven by a small electric motor and powered by batteries. Spray liquid flows onto the spinning disc/cup and is thrown off as spray droplets that are dispersed by the wind over a downwind swath. In fact, various types of rotary atomizer are used on the other categories of ULV locust sprayer (vehicle-mounted and aerial), and the term RA is used for this specific sprayer type in order to conform with the definition in previous volumes of the guidelines. RA sprayers are particularly useful - either singly or operated in formation by a team of operators - for control of relatively small hopper band targets (up to 5 ha). Such teams of operators can also be used to apply barriers over much larger areas.
Motorized mistblowers rely on an airblast from an engine-driven fan to atomize the pesticide and blow it some metres away from the sprayer operator. The term MB has the same meaning here as in the other guidelines, except that any motorized mistblower used for ULV locust control must have some modifications and supplementary features. These are ULV pesticide-resistant pipes, hoses and seals, usually a rotary atomizer mounted in the air tube rather than a standard air shear nozzle, and modified flow restrictors to provide the low flow rates required. They can be used to spray locusts in bushes and low trees or directed upwards in more open terrain to produce a greater effective emission height and therefore a wider swath and faster work rate than an RA sprayers. They are suitable for small hopper bands and fragments of settled swarm targets (up to 10 ha).
These can be thought of as RA sprayers adapted for vehicle-mounted use. They operate on the same principle of releasing spray droplets from a rotary atomizer passively into the air and allowing the wind to disperse them downwind over the swath. They differ from RA sprayers only in that vehicles have higher forward speeds, emission heights and carrying capacities. The higher forward speeds and emission heights mean that greater work rates can be achieved, in turn requiring a higher flow rate to take advantage of this. To cope with this higher flow rate and still maintain the quality of the droplet spectrum, atomizers are larger and tanks have greater capacity. A pump is used instead of gravity to feed the pesticide to the atomizer. They are suitable for medium sized targets up to 50 ha.
These can be thought of as MB sprayers adapted for vehicle use. They are similar to VP sprayers except that an engine-driven fan blows the spray from the rotary atomizer some metres from the sprayer. Track spacings wider than those for VP sprayers are possible due to the facility to direct the airblast upwards and carry the droplets to a greater effective emission height before they are released into the cross wind. VA sprayers are suitable for medium sized targets up to 100 ha.
For the purposes of these guidelines, locust sprayers can be divided into several component modules. Each module relates to a major component or a functional group of components from which consistent specifications for complete sprayers can be compiled. The specifications do not dictate or prescribe engineering design; they define functional or operational requirements and should not restrict the engineering design freedom of the manufacturer. The modules for locust and grasshopper sprayers are shown in Figure 1.
Figure 1. Component modules of locust and grasshopper sprayers