What is the ruling on scattering dust in the path of the envious person and fumigating with it?

Allah and the Prophet (peace be upon him) have taught us the way to prevent the evil of the envious, and what was mentioned in the question is not among the legitimate methods, for it scratches the creed and undermines the wall of monotheism. Muslims are in no need of these superstitions after Allah has enriched them with His Book and the Sunnah of His Prophet. Among the ways to prevent envy are: concealing blessings from those whose envy is feared, striving to show gratitude for blessings, and adhering to the prescribed remembrances and supplications for protection authentically narrated from the Prophet (peace be upon him), especially the two surahs of seeking refuge (Al-Mu'awwidhatayn).