Table 1 



Amount of 1 acre 
covered at contact 
angle - 9001 



Drops per square 
centimeter 
Drop diameter 
(microns) 



Mean distance apart 








Number Percent 
OM Metscse tices seeelsnner ss 2,213,500 266.0 
ZO a ardie abe arabs oinWs 267,000 133.0 
AORN ccte tocar a a asore srareds 33,350 66.5 
red okonas foi aveouefocsnete nena ts 5,600 35.5 
OO a crciecth cio cunt ¢ 2,135 26.6 
ANU Faro apoboodT Steere 267 13.31 
srote}e feserepelieyeiers ores 33, 
eevee eceeeeeee 

1 Por plant surfaces, these figures would have to be divided by the acres of plant sur- 
face per acre of land, which may vary from 5 to 20, and then multiplied by a spread factor 
corresponding to actual angle contact. 
In one project (30), Several series of ex- cide particles depend in some way on particle 
periments were carried out in which spray- size (15), For example, the smaller a pesti- 
droplet mass median diameter could be varied cide particle the greater will be the aero- 
by chosen increments, usually 100 microns dynamic drag forces compared with its inertia 
each, from 100 to 500 microns, (Mass median and the less will be its deposition from inertial 
diameter represents a measurement that means impaction; the greater will be the ther- 
that 50 percent of the volume of the spray is mophoretic repulsion from surfaces; and the 
contained in drops of less diameter than more one may have to depend, e.g., upon 
the stated diameter.) Throughout a series of electrostatic or other effects instead of gravity 
experiments extending over 10 years, these to obtain deposition, As a result, it may be 
research tests demonstrated that, on diseases difficult in certain cases to obtain anything 
of potatoes and on potato and tomato insects, resembling precise control of particle appli- 
virtually any combination of pressure and cation if we attempt to deal with an assort- 
volume that was used to obtain spray droplets ment of sizes, which may have a 200-1 range, 
between 100 and 500 microns gave approxi- such as in a conventional spray, 
mately the same control. The process that primarily has controlled 
Other research (11) has indicated that foliar spray and dust deposition in our past equip- 
applications of herbicides tended to be more ment has been inertial impaction, i.e., the 
effective as the herbicidal formulations were projection of a pesticide cloud in the direction 
decreased from 0.3 mm, down to 0,1 mm, in of the plant, Since this process is so widely 
diameter, used, it is surprising in retrospect that so 
It appears that in the future there may be a little work has been done on it from an 
greater tendency to try to control the size agricultural point of view. 
distribution of pesticide particles (15), The A method of pesticide application ofinterest 
development of granular materials is an ex- to, and under study by, several industrial and 
ample of this, because it was seen that it was research organizations is the electrostatic 
easier to make the particles behave in a cer- charging of pesticide particles, Experimental 
tain way when they were of arelatively narrow results have indicated that, under cetain con- 
particle-size distribution, Many processes that ditions, a significantly greater amount of ma- 
affect the behavior and the deposition of pesti- terial will be deposited on the plants when 
208 
