Method for treating phytopathogenic microorganisms using surface-modified nanoparticulate copper salts

A method for controlling phytopathogenic microorganisms by treating the crop to be protected, the soil or the plant reproduction material with an effective amount of amorphous copper salt particles, the amorphous copper salt particles being obtainable by a method comprising:

• a) preparing a first aqueous solution comprising copper ions and a second aqueous solution comprising at least one anion which is not hydroxide and forms a precipitate with copper ions, at least one of the first aqueous solution and the second solution comprising at least one water-soluble polymer,
• b) mixing the first aqueous solution and the second aqueous solution at a temperature in the range of from 0 to 100° C. to form an aqueous dispersion, and
• c) optionally concentrating the aqueous dispersion and/or removing by-products from the aqueous dispersion,
• where the copper salt particles have a primary particle diameter of from 1 to 200 nm.