NAVMED P-5010-8 - Navy Medicine - U.S. Navy

8-11 CHAPTER 8. NAVY ENTOMOLOGY AND PEST CONTROL TECHNOLOGY 8-12
d. Pesticide Dispersal. After the desired
formulations have been selected, prepared, and
procured, they may be dispersed in the following
forms:
(1) Gases and Vapors. The dispersal
of gases and vapors is termed fumigation. They
must be handled with great care and only under
direct supervision of specially trained and
certified personnel. Gases and vapors are able to
penetrate packaged commodities, clothing and
structures, which are inaccessible to treatment
by other dispersal methods. Because they lack
residual properties, fumigants are used when
other formulations are ineffective or because of
penetration requirements. However, because of
their physical properties, fumigants can be used
only in airtight spaces, which prevent dissipation.
One type of fumigation, known as
"vaporization," is accomplished by the use of
solids such as paradichlorobenzene (PDB),
which at room temperatures, passes from a solid
directly into a vapor (sublimation).
(2) Aerosols. Aerosols are defined as
a suspension of liquid or solid particles in air
where the particle size generally ranges from 0.1
to 50 microns in diameter with 80% of the
particles in the 0.1 to 30 micron range. Liquid
particles make up a fog and solid particles form
a smoke. Insecticide aerosols are frequently
dispensed from hand held pressurized containers
or larger ultra low volume (ULV) dispersal
equipment.
(3) Mists. Mists are dispersed
particles in which the particles are intermediate
in size between those of aerosols and fine
sprays. Droplets in the 50 to 100 micron size
range are considered to be mists. They are less
effective than aerosols for outside space
treatment, but they are adaptable for larviciding
in areas accessible to vehicles and for large scale
residual spraying of vegetation. Because of their
larger size, mists can be used under a wider
range of weather conditions than can aerosols,
and their residual effect is greater.
(4) Sprays. (The most commonly
used formulation.)
(a) Fine sprays. Fine spray
droplets are considered to be from 100 to 400
microns in diameter. Droplets within this range
remain airborne short periods of time and settle
rapidly. Sprays of this type are frequently used
as mosquito larvicides and for residuals.
(b) Coarse sprays. These sprays
consist of droplets over 400 microns in diameter
and are applied evenly to wet a surface. Coarse
sprays are frequently employed when using
herbicides and when applying heavy residuals of
insecticide to fly breeding areas.
8-12. Application of Pesticides
a. Effects of Particle Size. Efficient
application of pesticides requires the dispersal of
the proper particle size for the type of
application desired. The residual quality of
many insecticides makes it possible to kill by
contact long after the material has been applied
to walls, vegetation or other insect resting
places. In order to take full advantage of the
residual characteristics of a pesticide, it should
be applied only in the form of a coarse spray or
dust. By contrast, efficient use of space sprays
calls for their dispersal in much smaller
particles. Coarse sprays are inefficient aerosols
because the fewer number of droplets decreases
the chances of target contact. Those particles,
which do contact the target, may contain many
times the amount of insecticide needed to affect
a kill. Large particles fall to the ground while
small particles may remain airborne for
extended periods of time, providing more
opportunity to contact targets. In this respect
there is also a disadvantage in that unfavorable
air current or high wind velocity may cause
rapid dispersal of the droplets into the
atmosphere, and the small insecticide particles
may be transported to non-target areas. Under
favorable conditions, aerosols or fogs are quite
efficient for killing insects or other arthropods
by means of space treatment.
9 Nov 2004
8-11