Problem: Poa Annua
Poa annua Annual bluegrass is one of the most troublesome but least noticed weeds in the lawn. This member of the bluegrass family is lighter green, more shallow rooted, and less drought tolerant than Kentucky bluegrass. As its name suggests, annual bluegrass usually lives for only 1 year, although some strains are perennial. The seed germinates in cool weather from late summer to late fall. Annual bluegrass grows rapidly in the spring, especially if the lawn is fertilized then. Seed heads appear in mid- to late spring at the same height that the grass is cut. The seed heads give the lawn a whitish appearance. When hot, dry weather arrives, the plants turn pale green and die. The seeds fall to the soil and wait for cooler weather to germinate. Annual bluegrass is most serious where the soil is compacted or over-irrigated and where drainage is poor.
Correct compacted soil. Reduce the chances of invasion by allowing the soil to become moderately dry between waterings when the seeds are germinating in the fall. This will also provide a measure of control if the plants become stressed because of high temperatures and drought in the spring.