DIRECTIONS FOR APPLYING WINDBORNE AEROSOLS 
FOR INSECT CONTROL OUT oF DooRSL 
By A. H. Yeomans 
Entomology Research Division 
Windborne aerosols are those applied as a cloud and carried by the 
wind across the area treated. Insect control attained from windborne 
aerosols applied to field crops and orchards is due mostly to the 
deposit. However, if the aerosol is applied while the insects are in 
flight, individuals on the wing are killed as well as those that come 
in contact with the deposit. 
Machines for applying windborne aerosols are different from those 
that project sprays with a powerful air blast. The air-blast machine 
can provide a more nearly uniform deposit across a swath with the larger 
spray particles than can be obtained with the windborne aerosol machine. 
For satisfactory performance an aerosol cloud must be released 
under proper weather conditions, have uniform deposition in the selected 
swath width, be composed of particles of the proper size, be of the 
proper dosage and formulation, and be applied in the most economical 
manner. These requirements will be discussed. 
Weather Requirements 
Satisfactory movement of the aerosol cloud across the area is 
accomplished by making applications under the proper weather conditions. 
A light wind is needed, steady in direction, and moving at 1/2 to 8 mp.h. 
Winds slightly stronger than 8 mpeh.e can be utilized when the cloud is 
drifted uphill or when an orchard or other area with a high canopy is 
treated. A time of day should be selected when there is a surface 
inversion of temperature--i.e., when the air temperature is cooler at 
the ground level than at a height of 6 feet or more. Surface inversion 
keeps the aerosol cloud close to the ground and is most important when 
low-growing crops are treated and least important when trees having a 
canopy of foliage are treated. Good inversion usually occurs only at 
night from 1 hour after sunset until sunrise, but occasionally exists 
1/ This is a revision of ET-282, issued by the former Bureau of 
Entomology and Plant Quarantine in May 1950. 
