Clarification on pre emergent

[okgrassguy]

I have asked this elsewhere but thought I would ask those who would know the exact answer. Does pre emergent work by destroying any seed present, prevent germination leaving viable seed after it has worn off or does it destroy seedlings as they germinate.

[Gatewayuser]

What it does is destroy weeds on contact when they first emerge, its does NOT destroy seeds.

[SodKing]

Pendimethelin works by sloughing off the outermost layers of cells on the root hairs thus leading to the drying out and dessication of the root hairs and immature seedling.