Problem: Annual Bluegrass Dying
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.
When dead patches appear in hot weather, the annual bluegrass is dead. The lawn is laced with its seeds, however, which will germinate with cooler fall weather. Do not cut the lawn too short. Lawns more than 2 1/2 inches tall have very little annual bluegrass. Aerate the lawn in compacted areas.