A spraying liquid for combating pests comprises, in addition to an agent for combating pests, a hardenable amino-plastic, i.e. a derivative obtained by reacting formaldehyde with a compound containing an amino-group and which is water soluble or of limeted solubility in water, and a proportion of a hardening accelerator amounting to at least 4 per cent by weight of the total content of non-aqueous constituents of the spraying liquid, and has a pH value not lower than 5. Specified aminoplastics are obtained by condensing formaldehyde with urea, thiourea, cyanamide, dicyandiamide, dicyandiamidine, melamine or mixtures of such condensates and include dimethylolurea, monomethylolthiourea, a dicyandiamide-urea-formaldehyde condensation product, and hexamethylolmelamine - ethylene glycol ether. Specified hardening accelerators are ammonium chloride, sulphate, oxalate, lactate, ammonium salts of organic sulphonic acids and potassium persulphate. The pesticide may be a fungicide or insecticide such as copper oxychloride, lead arsenate, barium fluosilicate, sulphur, D.D.T., 3.6-dinitro-monochlorocarbazole, 2.4-dinitro-thiocyano-benzene, tetramethyl-thiuram mono- or disulphide mixtures of such compounds, or the ammonium salt of 2-oxy-3.5-dinitrotoluene, xanthone or phenothioxine. Optional additions include kaolin, gypsum, bentonite, sulphite cellulose waste liquor, sodium dipropylnaphthalene sulphonate, a condensation product of naphthalene sulphonic acid and formaldehyde, methyl cellulose, and the methyl ammonium sulphomethylate of oleyl-diethylethylene diamine. The spraying liquid may be prepared by mixing the pesticide with the hardening accelerator, stirring the mixture with water and adding the hardenable aminoplastic to the resulting liquor; by mixing the pesticide with the hardenable aminoplastic, stirring the mixture with water and adding a hardening accelerator to the resulting liquid, or by forming a dry composition by mixing the pesticide, the hardenable aminoplastic and the hardening accelerator and mixing this composition with water. Hexamethylolmelamine-ethylene glycol ether is prepared by heating an aqueous formaldehyde solution having a pH of 8.5 with melamine at 70 DEG C. while stirring, evaporating water at reduced pressure, mixing the resulting paste with methanol and ethylene glycol, heating the mixture under reflux at 85 DEG C., adding methanol containing hydrochloric acid, further heating at 80-85 DEG C., removing the mixture of methanol and water by distillation under reduced pressure, and adjusting the pH of the residue to 8.5 by the addition of caustic soda to produce a clear, thick syrup. A dicyandiamide-urea-formaldehyde condensation product is prepared by stirring dicyandiamide and urea with aqueous hydrochloric acid under reflux first at 50-60 DEG C. and then at 125-135 DEG C., cooling to room temperature, adding aqueous formaldehyde, stirring the mixture at 75-85 DEG C., cooling to room temperature and adding ammonia solution. A thiourea-formaldehyde condensation product in admixture with other ingredients is obtained by stirring thiourea, copper oxychloride, the mono-oleyl-diethylethylene diamine salt of methyl ammonium sulphomethylate, methyl cellulose and ammonium sulphate into a large quantity of water and then adding paraformaldehyde.ALSO:Dimethylolthiourea in aqueous solution is prepared by stirring aqueous formaldehyde with a small quantity of magnesium oxide until a weakly alkaline reaction is obtained, adding thiourea, stirring for one hour at 40-50 DEG C. and filtering. Specification 587,263, [Group VI], is referred to.ALSO:A spraying liquid for combating pests comprises, in addition to an agent for combating pests, a hardenable aminoplastic, i.e. a derivative obtained by treating formaldehyde with a compound containing an amino-group and which is water soluble or of limited solubility in water, and a proportion of a hardening accelerator amounting to at least 4 per cent. by weight of the total content of non-aqueous constituents of the spraying liquid, and has a pH value not lower than 5. Specified aminoplastics are obtained by condensing formaldehyde with urea, thiourea, cyanamide, dicyandiamide, dicyandiamidine, melamine or mixtures of such condensates and include dimethylolurea, monomethylolthiourea, a dicyandiamide-urea-formaldehyde condensation product, and hexamethylol-melamine-ethylene glycol ether. Specified hardening accelerators are ammonium chloride, sulphate, oxalate, lactate, ammonium salts of organic sulphonic acids and potassium persulphate. The pesticide may be a fungicide or insecticide such as copper oxychloride, lead arsenate, barium fluosilicate, sulphur, D.D.T., 3.6-dinitro-monochlorocarbazole 2.4-dinitro-thiocyano-benzene, tetra methylthiuram mono-or disulphide, mixtures of such compounds, or the ammonium salt of 2-oxy-3.5-dinitrotoluene, xanthone or phenothioxine. Optional additions include kaolin, gypsum, bentonite, sulphite cellulose waste liquor, sodium dipropylnapthalene sulphonate, a condensation product of napthalene sulphonic acid and formalthehyde, methyl cellulose, and the methyl ammonium sulphomethylate of oleyl-diethylethylene diamine. The spraying liquid may be prepared by mixing the pesticide with the hardening accelerator, stirring the mixture with water and adding the hardenable aminoplastic to the resulting liquor; by mixing the pesticide with the hardenable aminoplastic, stirring the mixture with water and adding a hardening accelerator to the resulting liquid, or by forming a dry composition by mixing the pesticide, the hardenable aminoplastic and the hardening accelerator and mixing this composition with water. Specification 587,263 is referred to.