a ees 
all day when the ground has been cooled by rain. In hilly terrain sur- 
face inversions usually occur only in the valleys. If it is necessary 
to make treatment in the daytime without the surface inversion, a wind 
of 5 to 10 mph. is beneficial. 
Deposition 
The deposit is heaviest nearest the point of release and decreases 
as the distance increases, because the larger particles settle out first. 
Aerosol particles moving with the wind deposit selectively on exposed 
vertical surfaces but settle uniformly on horizontal surfaces. The amount 
of deposit on the vertical surface depends on the size and shape of the 
object. Under similar conditions the deposit is much greater on objects 
of narrow width, such as pine needles, than on ones of greater width, 
such as maple leaves. The deposit on vertical surfaces becomes important 
when the aerosol is applied in winds stronger than 5 m.pehe, and on small 
tender foliage it is sometimes heavy enough to cause injury. When a 
large proportion of the foliage is exposed vertically, as ina vineyard, 
the increased deposition is especially important. 
Experience has shown that under the best conditions only 25 to 50 
percent of an aerosol containing particles of less than 50 microns mass 
median diameter deposits in swaths up to 2,000 feet, the major portion 
drifting beyond the area under treatment. 
The deposits of aerosols of different particle size released in a 
3-m.peh. wind under good inversion conditions are given in table l. 
These deposits settled on an open field; the percentage would have been 
higher if the aerosol had been released through dense foliage. 
Table 1.--Effect of particle size on the percent of total insecticide 
depositing on 100-foot strips across a field 


Mass median diameter of particles 
Distance from release 
front (feet) 


0-100 25.8 726 1.4 
100-200 16.6 7.5 1.4 
200-300 aie 6.5 Dolh 
300-400 545 lest 1.4 
100-500 2.8 2 yA 
500-600 ah ee 1.4 
600-700 0.9 ie 7 alah 
700-800 05 17 1.0 
800-900 25 U7 0.7 

