of treatment include quick knockdown without use of a residual and quick killing effect.
It is effective against flying insects and pests that cannot be seen.
2-13. PESTICIDE DISPERSAL METHODS
a. Spraying. Spraying was originally defined as the application of liquid
pesticides, but, with recent developments, it is now defined as application of liquids
atomized into droplets 100 microns in diameter or greater. Sprays can be further
classified into fine sprays (100-400 microns in diameter) and coarse sprays (400
microns in diameter or greater). Due to the larger size of the droplet, sprays fall out of
the air rapidly; hence, they can be used under a wide range of weather conditions.
Generally, sprays are applied in low concentrations and under low pressure. Spraying
is used to apply residual pesticides to surfaces, either body surfaces (of pests) or
surfaces that pests will contact or ingest at a later time.
b. Misting. Misting is the dispersal of liquid pesticides with a droplet size of 50
to 100 microns in diameter. These droplets are still heavy enough to settle out;
however, they remain airborne longer than sprays. Mists are usually applied at higher
concentrations and penetrate better than sprays. They are effective both as an outside
residual and space treatment and are occasionally used indoors.
c. Aerosoling. Aerosoling is a method for dispersing suspensions of solid or
liquid particles that are less than 50 microns in diameter. This can be accomplished
either through thermal or cold aerosoling techniques. Thermal fogging (aerosoling)
uses either hot gases or super heated steam, which gives the distinct appearance of
dense white fog. Cold aerosoling is accomplished by combining the pesticides with a
liquid that boils at a low temperature and discharging the mixture by its vapor pressure
through a small orifice or by using mechanical shearing. Ultra-low volume (ULV) and
ultra-low dosage (ULD) are included in this dispersal method; however, their particle
size range is usually 5-30 microns. Aerosoling is an effective method of dispersing
space sprays since it leaves virtually no residual and remains airborne for longer
periods of time. Aerosols have excellent penetration and, due to their small particle
size, are significantly influenced by weather conditions. Because of the latter fact, ULV
dispersal can be accomplished only under certain weather conditions: air temperature
less than ground temperature; air temperature between 40 and 85F; and wind speed
less than 10 mph. ULD aerosols are used indoors for control of flying insects and
exposed stages of crawling insects (stored product pests, cockroaches, flies, etc.). ULV
aerosols are used outdoors for control of mosquitoes and biting flies. This method of
dispersal may be repeated as often as necessary because there is no residual.
d. Fumigation. This method of dispersal involves the use of gaseous poisons
that are molecular in size. Since these gases are hazardous to all life forms, they must
be used with extreme care. Gases are able to penetrate packaged commodities,
clothing, and structures inaccessible to sprays, mists, and aerosols and, therefore, must
be confined under a tarp or other impermeable enclosure. The two major advantages of
this dispersal method are that the molecules pass directly through the pest's body wall