Kentucky bluegrass is currently producing seedheads that are difficult to mow and create an uneven appearance. However, annual bluegrass (Poa annua) is also producing similar looking seedheads. It’s important to distinguish the two because Kentucky bluegrass is highly desirable in a lawn, but annual bluegrass is a weed. It is a weed because it is a winter annual or weak perennial 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 (photos). 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.
https://mdc.itap.purdue.edu/item.asp?item_number=ay-41-w
