of the particulating agent employed, The par- 
ticulated solution is then spray applied, 
The mechanism of action postulated for 
particulate sprays suggests that an optimum 
amount of particulating agent in a solution 
would leave little solution free to form very 
small droplets. Consistency ofthe solution then 
should be directly related to effectiveness in 
reducing spray drift potential, Tests have shown 
that the spray produced has much less volume 
of small droplets than does a comparable 
solution containing no particulating agent, 
Particulate sprays have effected a major re- 
duction in drift in each test, but quantita- 
tive correlation was not possible, because the 
particulate spray reduced drift to a point 
beyond the detection level of the sensitive assay 
method employed in the field experiment (7), 
Another interesting attempt to decrease 
spray drift is brought about by increasing the 
viscosity of the spray liquid by producing a 
water-in-oil emulsion, popularly known as an 
invert emulsion, This method helps to reduce 
the number of small droplets in sprays, 
Soil Fumigation 
A special case of pesticide application re- 
lates to subsurface application of pesticides 
for control of diseases or soil-located insects, 
Several of the soil fumigants are extremely 
corrosive, and engineers must provide proper 
structural materials resistant to corrosion, 
Some highly volatile fumigants must be re- 
tained in the soil by polyethylene covers, and 
special precautions must be followed in de- 
velopment of equipment, as some of the ma- 
terials are very toxic, 
Attraction of Insects With Audible 
and Ultrasonic Sound Waves 
A recent report (6) describes an investiga- 
tion of the tendency of sound and ultrasonic 
radiation to attract the ordinary house fly. 
Radiations from 180 to 40,000 c.p.s, at two 
intensity levels were used in the trials, The 
results of the experiment indicated that the 
insects did have sound responses, but further 
investigation is necessary before recommen- 
dations can be made, 
It has also been reported that sound has been 
effective in repelling rats, mice, and other 
211 
rodents, For example, a small unit with a 
frequency range from 17 to 26 kc, per second 
was reported to protect an area up to 40,000 
square feet, A built-in system continuously 
shifts frequencies, so that the rodent will not 
become accustomed to one particular fre- 
quency, 
Special Problems 
One of the earliest means for insect con- 
trol was the application of tillage techniques 
to reduce grasshopper infestations, Beforethe 
advent of good pesticides and pesticide appli- 
cation equipment, deep plowing was recom- 
mended to help prevent serious grasshopper 
infestations, Stubble fields were tilledin strips, 
so that more favorable egg-laying conditions 
existed in specific areas, which were sub- 
sequently given the proper tillage treatment 
to reduce the insect population, 
Flame cultivation of Some crops, particularly 
cotton, is effective for controlling weeds and 
thus results in the application of less chemi- 
cals, Eradication of weeds in cultivated crops 
by flaming is now standard procedure in some 
areas (30), Different kinds of plants are able 
to withstand amounts of heat depending on their 
stem structure, age, size, and shape, The 
intensity and volume of the flame and duration 
of exposure are important factors in attaining 
effective results, Detailed experiments have 
been carried out to determine the temperature 
patterns resulting from different experimental 
burners, which are then modified to produce 
more efficient flame nozzles, 
Engineers have experimented with infrared 
radiation for rice drying and steam condi- 
tioning of tobacco in a vacuum to destroy 
insects in the stored commodities, 
Although we generally think of pest control 
with respect to the principal farm operations, 
there is a major job to be done with respect to 
engineering in the development of equipment 
for the application of pesticides around the 
home (8), The home gardener and the indi- 
vidual who takes care of his lawn and shrub- 
bery are greatly concerned with techniques 
and equipment for control of pests, One writer 
(8), suggests, perhaps with tongue in cheek, 
that one of the biggest single handicaps in 
weed control is the complete lack of really 
