Also known as Annual Bluegrass, this grassy weed can be brought into your lawn by wind, birds, commercial lawn mowers, foot traffic and impure seed. The seeds can lay dormant for several years before sprouting. It is identifiable by seed heads at a very low level. It is very aggressive and will turn brown in the heat. It can be pre-emergently treated in the fall with Green-Up Lawn Food with Crabgrass Preventer or Crabgrass and Weed Preventer or Organic Weed Preventer. If you do this, you cannot overseed in the fall.