Though he be fruitful among his brethren, an east wind shall come, the wind of the LORD shall come up from the wilderness, and his spring shall become dry, and his fountain shall be dried up: he shall spoil the treasure of all pleasant vessels. Though he be fruitful - יפריא yaphri; a paronomasia on the word אפרים ephrayim, which comes from the same root פרה parah, to be fruitful, to sprout, to bud.
An east wind shall come - As the east wind parches and blasts all vegetation, so shall Shalmaneser blast and destroy the Israelitish state.