4 As the month of October again approaches, Venerable Brethren, We would not willingly leave you without Our letters this year, also once more urging you with all possible earnestness to strive by the recitation of the Rosary to aid both yourselves individually, and the Church in her need. This form of prayer appears, under the guidance of Divine Providence, to have been wonderfully developed at the close of the century, for the purpose of stimulating the lagging piety of the faithful. This is witnessed by the splendid churches and much-frequented sanctuaries of the Mother of God. To this Divine Mother we have offered the flowers of the month of May; to her we would have also fruit-bearing October dedicated with especial tenderness of devotion. It is fitting that both parts of the year should be consecrated to her who said: "My flowers are the fruit of honour and riches" (Ecclus. xxiv., 23).
Source: Augustissimae Virginis Mariae (Vatican.va)