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

8-12 CHAPTER 8. NAVY ENTOMOLOGY AND PEST CONTROL TECHNOLOGY 8-12
b. Effect of Meteorological Conditions.
There are many conditions, which may improve
or reduce the effectiveness of the pest control
program. In addition to knowledge of the life
history of the pest to be controlled, the proper
choice of control technique, pesticide, and
dispersal equipment, it must be remembered that
meteorological conditions such as convection,
relative humidity, wind velocity and direction,
and temperature may add to the complexity of
outdoor space spray operations.
(1) Convection. Once the pesticide is
released from the nozzle, meteorological
conditions are the only forces acting upon the
particles. One of the most important of these is
convection, or the upward and downward
movement of a limited portion of the atmosphere.
Convection influences the deposition of
particles on the surface of the ground, foliage or
target pest according to the existing temperature
conditions. When the ground temperature is at
least one degree cooler than surrounding air
(inversion), aerosol droplets tend to drift near
the ground within the habitat where the target
species is most likely to be contacted. Coverage
of the area will generally depend on the wind
conditions at the time. When the ground
temperature is warmer than the air (lapse
condition), small droplets in the mist and aerosol
range, tend to be carried up and out of the target
zone by convection currents. Measurements of
temperature to determine inversion or lapse
conditions may be accomplished by using
thermometers placed 0.3 and 1.8 m (1 and 6 ft)
above the ground.
(2) Wind. A fine spray or dust will
be scattered over a very wide area during a high
wind especially under lapse temperature
conditions. On the other hand, a lack of air
movement will limit the pesticide distribution.
Normally, it is an advantage to conduct outdoor
space dispersal of aerosols if the movement of
air is about 1 to 7 knots in a direction perpendicular
to the line of dispersal (discharge from
nozzle) and toward the area to be treated.
(3) Temperature. Some pesticides
may be more effective when air temperatures are
21 degrees C. (70 degrees F.) or above while
others are more effective at lower temperatures.
Pesticide labels can provide information
regarding the influence of temperature on
control.
c. Selection of Method. Before a
control operation is undertaken, one must
determine if chemical control of the pest is the
most satisfactory approach. Chemical control is
the most expensive yet least permanent of the
various methods of pest control. It should only
supplement, not replace other pest control
procedures. However, there are many situations
where pesticides are valuable tools in the pest
control program, such as during the threat of
outbreak of vector-borne disease. Even during
such times, control personnel should not lose
sight of long range and more permanent
measures.
(1) Preventive Control. Quarantine,
drainage, impoundment, flushing, flooding,
ditching, screening, sanitation, etc., are basic
practices in the prevention of pest infestations.
These methods of control are expensive initially
but are the least costly and most effective over a
long period of time. When military bases are of
a permanent type, these methods are preferred.
(2) Chemical Control. To employ
chemical control measures is to admit the
preventive measures are not adequate. This
method of pest control is the most common and
expensive, and it is temporary at best. In most
field operations, when the site is to be occupied
for short periods of time, chemical controls are
used almost exclusively. Corrective controls are
used until preventive controls are established
and then only to augment more desirable
methods of pest control. However, under
combat conditions, chemical control may be the
method of choice because of the need to rapidly
reduce the vector population and because
permanent control measures may be impossible
due to lack of security.
8-12
9 Nov 2004