Thus, we need research to obtain for each pest-pesticide qualitative or quantitative 
curves showing the relationship between biological reaction and particle size. While we 
would expect the biological action to improve as the particles become finer, perhaps 
there would be a point below which the biological reaction would not greatly improve. 
This we would then consider the optimum particle diameter for controlling this particular 
pest with this particular pesticide. It would be the largest particle which would provide 
reasonable control. We would then aim to divide our pesticide into particles all of 
which were approximately this size. 
Another problem would then present itself. When we try to produce a large number 
of small particles of a particular size, we do not get a single size particle but a wide 
range of particle sizes. Generally we find that the particle size distribution we get is 
some type of logarithmic normal distribution. This distribution when plotted on con- 
ventional scales looks like illustration (left) below. When plotted on logarithmic scales, 
it will appear as illustrated (right) below. This distribution has the characteristic that 
a great many small droplets constitute a small percentage of the total volume and, 
conversely, a relatively small number of droplets make up a large percentage of the 
total volume of spray. From our discussion of the effect of various forces on droplets 
of different sizes we can see that this large number of small droplets is undesirable. 
5 50 500 5000 
S00 1000 | 1§00 2000 
Number of Drops 
It is reasonable to ask why we get such a distribution of particle sizes. Apparently 
it is due to the fact that the particle size depends upon a number of variables, each of 
which in turn is subject to random variation. 
What can be done to minimize the geometric standard deviation of this logarithmic 
normal distribution, or what can be done to reduce the tendency towards a log normal 
distribution itself? To reduce the variability of a drop size distribution caused by some 
drop formation process we could do two things. We could minimize the variability 
of each of the components variables which affect the process, and we could reduce the 
number of variables. Reducing the number of variables which affect the process should 
also tend to make the drop size distribution less nearly log normal. 
Measurement of Mass and Particle Size Distribution. The problem of measuring 
chemical distribution is one of our most critical because all other research hinges upon 
it. This will include highspeed measurement of particle size distribution, quantitative 
measurement of chemical distribution on the soil, and quantitative mass distribution of 
chemicals on plant surfaces. Until we have these methods available, all other research 
on pesticide application equipment will have a corresponding lack of precision. 
In addition, the effect of natural meteorological conditions upon pesticide applica- 
tion requires further research. This includes study of the velocity, scale and distribution 
of atmospheric turbulence, and the effect of humidity on electrostatically charged particles. 
Particle adhesion. Despite its great importance to pesticide application we have 
almost no basic information on the adhesion of particles for various surfaces. Most of 
the basic work which has been done so far on particle adhesion has been done by the 
people working on air filters. Research is badly needed on physical mechanisms in the 
retention of materials on plant surfaces, 
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