they - the “princes and judges” (Isa 40:23) who oppose God’s purposes and God’s people. Often compared to tall trees (Psa 37:35; Dan 4:10).
not ... sown - the seed, that is, race shall become extinct (Nah 1:14).
stock - not even shall any shoots spring up from the stump when the tree has been cut down: no descendants whatever (Job 14:7; see on Isa 11:1).
and ... also - so the Septuagint. But Maurer translates, “They are hardly (literally, ‘not yet’, as in 2Ki 20:4) planted (etc.) when He (God) blows upon them.”
blow - The image is from the hot east wind (simoon) that “withers” vegetation.
whirlwind ... stubble - (Psa 83:13), where, “like a wheel,” refers to the rotatory action of the whirlwind on the stubble.