Cogongrass is worrysome enough to have a dedicated website - http://www.cogongrass.org/. There could be as much as a million acres of the invasive grass in the twelve southern states.
Cogongrass grows into a flamable mat of grass that creates intense, tree killing heat when on fire. It can be a nightmare for mowing equipment and without chemical eradication, will totally take over the forest floor and prevent any and all efforts to grow trees. This is not good news for Southern forests.
Identifying Cogongrass in Alabama - Photo by Steve Nix, Licensed to About.com