Though he is fruitful among his brothers, an east wind will come, The breath of Yahweh coming up from the wilderness; And his spring will become dry, And his fountain will be dried up. He will plunder the storehouse of treasure.
Like almost every other verse in Hosea, there is a reflection of the Pentateuch here.  The reference to Ephraim as "fruitful" harks back to the patriarchal blessing of Ephraim by Jacob  (Genesis 48:19).  The very name Ephraim means "fruitful."