Non-volatile slow-release pesticidal generators

A method for preventing the release of .beta.-2-chloro-1-(2,4,5-trichlorophenyl)-vinyl dimethyl phosphate from within, onto the surface of a solid composition consisting essentially of a pesticidally effective amount of from about 3 to 30% by weight of the total composition of said .beta.-2-chloro-1-(2,4,5-trichlorophenyl)-vinyl dimethyl phosphate dispersed in a matrix of plasticized thermoplastic resin compatible with said phosphate and capable of releasing a pesticidally effective amount of said phosphate onto the surface of said composition, said composition having on the surface thereof a polymorphic form of .beta.-2-chloro-1-(2,4,5-trichlorophenyl)-vinyl dimethyl phosphate characterized by a needle-like crystalline structure, which comprises subjecting said composition to an elevated temperature for a period of time sufficient to convert substantially all of said .beta.-2-chloro-1-(2,4,5-trichlorophenyl)-vinyl dimethyl phosphate in said needle-like polymorphic form to a polymorphic form characterized by a platelet-like crystalline structure and a melting point of 95.degree.-98.degree.C, the presence of said latter polymorphic form serving to inhibit the migration of further quantities of .beta.-2-chloro-1-(2,4,5-trichlorophenyl)-vinyl dimethyl phosphate from within the matrix onto the surface of said composition.

A method of inducing the release of .beta.-2-chloro-1-(2,4,5-trichlorophenyl)-vinyl dimethyl phosphate from within, onto the surface of a storage stable, slow-release pesticide composition consisting essentially of a pesticidally effective amount of from about 3% to 30% by weight of the total composition of said .beta.-2-chloro-1-(2,4,5-trichlorophenyl)-vinyl dimethyl phosphate dispersed in a matrix of plasticized thermoplastic resin compatible with said phosphate and capable of releasing a pesticidally effective amount of said phosphate onto the surface of said composition, the composition having on its surface said .beta.-2-chloro-1-(2,4,5-trichlorophenyl)-vinyl dimethyl phosphate in a polymorphic form characterized by a platelet-like crystalline structure and a melting point of 95.degree.-98.degree.C, which method comprises disturbing the surface of said composition so as to remove said .beta.-2-chloro-1-(2,4,5-trichlorophenyl)-vinyl dimethyl phosphate in said polymorphic form therefrom, thereby permitting the migration of further amounts of .beta.-2-chloro-1-(2,4,5-trichlorophenyl)-vinyl dimethyl phosphate from within said composition.