Annual bluegrass

Image by: James Altland, USDA-ARS
Annual bluegrass generally forms small clumps of grass that can overcome a small nursery container if left untreated.
Image by: James Altland, USDA-ARS
Image by: James Altland, USDA-ARS
A unique characteristic of annual bluegrass is the tips of the foliage look like canoes.
Image by: James Altland, USDA-ARS
Image by: James Altland, USDA-ARS
Inflorescences are generally pyramidal, grow only slightly larger than the foliage, and are white in color.
Image by: James Altland, USDA-ARS
Image by: James Altland, USDA-ARS
The flowering structure of annual bluegrass is a terminal panicle that can vary from 1 to 4 inches in length.
Image by: James Altland, USDA-ARS
Poa annua
Family: 
Poaceae
Life cycle: 
Annual
Habit: 
Annual bluegrass generally forms small clumps of grass. Each clump is 4 to 6 inches tall and wide, though many clumps often grow together forming larger masses.
Flowers: 
The white inflorescence is a terminal panicle that grows only slightly larger than the foliage. Seed head formation can start as soon as plants are 6 weeks old.
Favorable environments: 
Container
Favorable environments: 
Field
Favorable environment notes: 
Annual bluegrass is commonly found in many agricultural areas including gardens, landscape areas, nursery field plantings, vegetable crops, vineyards and orchards. It will establish in almost any disturbed soil area. It can also become quite problematic in golf courses and other turf areas. It has become resistant to several herbicides in the PNW.
Dissemination: 
Annual bluegrass is a very prolific seeder. Each small plant can produce about 100 seeds in as few as 8 weeks. Seeds are commonly spread by mowing, foot traffic, birds, and cultivation. Viable seed will remain in soil until needed moisture and temperatures encourage germination.
Of interest: 
Annual bluegrass has a shallow root system and needs consistent moisture to live through hot summer periods. Irrigated nursery areas are ideal environments for annual bluegrass to thrive. It can also be a major problem in turf grass areas such as golf courses and sports venues.