Kentucky bluegrass (Poa pratensis) is beginning to produce seedheads this time of year which are difficult to mow and can cause a lawn to appear uneven. However, there are other grasses such as annual bluegrass (Poa annua) that also produce similar looking seedheads. Annual bluegrass is a winter annual or weak perennial turfgrass species which invades highly managed lawns and often dies during summer heat and drought leaving behind a lack-luster lawn. Annual bluegrass usually has a lighter lime-green color than Kentucky bluegrass, but for a positive identification you need to take a closer look at the ligule. The ligule is an appendage at the base of the leaf blade that is long and membranous (it looks like scotch tape) on annual bluegrass, but is short or absent on Kentucky bluegrass. If you do suspect that annual bluegrass has invaded your lawn, then see the linked publication below for more information on identifying and controlling annual bluegrass.
Aaron Patton, Assistant Professor/Turfgrass Extension Specialist