# They are barely planted, barely sown

"As soon as someone plants them ... as soon as someone sows them" 

# he blows upon them

The prophet speaks of Yahweh removing the rulers from power as if Yahweh were a scorching wind that blows upon the plants and causes them to wither. 

# the wind carries them away like straw

The wind of Yahweh's judgement will remove the withered plants as easily as wind blows away straw.