Naturalization records

Guiseppe Verdi (Joseph Verdi) came to America from Genoa, Italy circa 1950. We don't know when he was naturalized and have had trouble finding this information.

His birthday is November 3, 1916.  He lived in Chiavari, Genoa, Italy.

Does anyone know how we can obtain this information?

Thanks,

Sheila Rothenberg

Manny Verdi