Method of electrostatically enhancing deposition of air borne spray materials

In the spraying of particulate material to ground from an airplane flying in close proximity thereto, the steps of

• imposing an electrical charge of given polarity upon a primary spray of particulate material continuously emitted from the underside of said airplane and at a location well forward of the tail section thereof, said charge being of sufficient magnitude to electrostatically enhance the deposition of said emitted primary spray particles, and
• concurrently physically and continuously emitting a secondary spray of oppositely charged particulate material in the form of a rearwardly directed jet from the tail section of said airplane at a location disposed well above the locus of emission of said primary spray and at a current level of a magnitude to avoid material degradation of the charge on said primary spray intermediate its loci of emission and deposition and at a charge to mass ratio of at least three times greater than the charge to mass ratio for said primary spray
• said secondary spray particles being from 0.1 to 50 microns in diameter and having, under ambient conditions, a mobility no greater than 10.sup.-5 meters per second per volt per meter and a useful life of at least one second after emission so that at least the major portion of the charged primary spray particles will be deposited without neutralization of the charge thereon by interaction with said secondary spray particles.