particles are charged. Several companies are 
now manufacturing dusters that use electro- 
static charging as a means of improving 
deposition, Some of the dusters are undergoing 
testing, whereas others have been put into use, 
Further research is indicated to obtain a 
better picture of the way in which this force 
may be used, 
Electrostatic, gravitational, and thermal 
forces and inertial effects need to be ex- 
plored over a wide range of particle-size 
distributions and turbulence conditions with 
various kinds of particles, including dusts, 
sprays, and fogs, The attainment of any signifi- 
cant increases in pesticide application ef- 
ficiency will depend on the knowledge of how to 
control and to apply these forces and effects, 
Measurement and Evaluation 
The problem of measuring chemical dis- 
tribution is one of our most critical because 
all other research hinges upon it, This will 
include high-speed quantitative measurement 
of particle distribution on plant surfaces and 
mass measurement of chemical distributionon 
and in the soil, Until we have these methods 
available, all other research on pesticide ap- 
plication equipment will have a corresponding 
lack of precision, 
Accurate and rapid measurement of particle- 
size distributions is quite difficult, and rela- 
tively little has been done in this field. Most 
measurements have been made by direct 
microscopic particle sizing and counting, This 
is a tedious and expensive procedure and is 
subject to error as well, both in sizing and in 
sampling, Other sizing methods, such as air 
classifiers, sedimentation systems, and light- 
scattering and electrical sensing instruments, 
have been applied, In the U.S, Department of 
Agriculture, as previously indicated, an auto- 
matic scanning method will be usedto study the 
details of particle distribution on surfaces, as 
well as in the determination of particle-size 
distributions. 
It would be helpful to be able to compare 
the biological effectiveness of different appli- 
cation methods and the physical performance 
of the various machines, Biological differ- 
ences might then be identified with physical 
differences, which might be common to several 
209 
methods or machines or both, If an important 
effect was found to be general, a principle 
could be established that could be utilized in 
other situations, However, the biological effect 
of an insecticide, for example, is in part 
dependent on the distribution of the insecticide 
on or in the insects, and this is rarely 
measured, We only infer that the insecticide 
is available whenever the insects die and vice 
versa, 
Rapid and accurate methods for calibration 
and for estimating the efficiency of pesticide 
application equipment are still needed and are 
not readily available, Individuals attempting to 
develop better methods and equipment for pesti- 
cide application, including the biological spe- 
cialist who wishes to observe the toxic ef- 
fects, need to take dozens and perhaps hundreds 
of samples of deposits on and around the plant, 
animal, or other object being treated. There 
may be a need to make rather difficult quanti- 
tative analyses of the amount of material on 
each sample in order to get a measure of the 
performance of a single pesticide application 
method (15), Various new methods for meas- 
urement of pesticide deposition have been 
proposed, including fluorescent tracers, chem- 
ical tracers, and radioisotope activation 
analysis, Engineers are frequently bothered 
by the fact that they do not have good sta- 
tistics on the percentage of pesticide that 
actually reaches the plant or eventhe principal 
types of spraying equipment used on the major 
crops, The difficulty in obtaining a quanti- 
tative measurement of any newimprovement in 
application equipment is obvious when that of 
present equipment is scarcely known, 
The only really practical method of deter- 
mining equipment performance in the field 
would be one that would provide a nearly in- 
stantaneous numerical reading of the deposit 
on a group of targets placed in selected loca- 
tions, With such an instrument, one could 
analyze the deficiencies of present equipment 
and could compare the effectiveness of various 
technique and equipment modifications, If such 
an instrument, or set of procedures, is ever 
realized, it will probably be the result of 
public service research, since the amount of 
investment industry can afford to make on this 
type of work is restricted (10), 
There is every likelihood that as time goes 
on the need will be for greater and greater 
