Poa annua is an annual weed, typically known as bluegrass, often found in lawns and gardens.  It is difficult to control because of the large number of seeds it can produce, which have the ability to remain dormant several years without sprouting.

The grass is generally found late spring to early summer and can be recognized by its tasseled seed stems sticking above the grass.

A pre-emergent herbicide is generally used to control germination of the poa annua seeds.  Due to their hardy nature and ability to survive several seasons, the lawn will need to be treated multiple years to rid the lawn of the weed.  Other herbicides can selectively kill poa annua in a lawn, but are required to be applied by certified professionals.