In midspring, abundant seed heads give the grass a whitish appearance. The pale green grassy weeds grow among more desirable grasses. They turn yellow and die with the onset of hot weather. Poa annua (annual bluegrass) seed germinates in cool weather from late summer to late fall. The grass grows rapidly in the spring, especially if the lawn is fertilized. Seed heads appear in mid- to late spring, giving the lawn a whitish appearance. When hot, dry weather arrives, the plants turn pale green and die.
Replace dead areas in the summer with sod. Do not cut the lawn too short. Lawns more than 2 1/2 inches tall have very little annual bluegrass. Annual bluegrass is most serious where the soil is compacted or over-irrigated and where drainage is poor. Aerate the lawn in compacted areas. Allow enough time between waterings for the surface of the ground to dry.