In 1889, in Quamquam pluries, Pope Leo XIII prescribed that this prayer to St. Joseph be added to the recitation of the Rosary during the month of October. Nothing prevents this prayer from being used by the faithful at any other time.)
Prayer to St Joseph for the Month of October: To thee, O blessed Joseph, do we have recourse in our tribulation, and having implored the help of thy thriceholy Spouse, we confidently invoke thy patronage also. By that charity wherewith thou wast united to the Immaculate Virgin Mother of God, and by that fatherly affection with which thou didst embrace the Child Jesus, we beseech thee, and we humbly pray that thou wouldst look graciously upon the inheritance which Jesus Christ hast purchased by His Blood and assist us in our needs by thy power and strength. Most watchful guardian of the Holy Family, protect the chosen people of Jesus Christ; keep far from us, most loving father, all blight of error and corruption: mercifully assist us from Heaven, most mighty defender, in this our conflict with the powers of darkness; and, even as of old thou didst rescue the Child Jesus from the supreme perils of His life, so now defend God’s Holy Church from the snares of the enemy and from all adversity; keep us one and all under thy continual protection, that we may be supported by thine example and thine assistance, may be enabled to lead a holy life, die a happy death, and come at last to the possession of everlasting blessedness in Heaven. Amen.
Original source can be found here.