Poa annua is a winter annual low-clumping grass that grows about 2.5-30 cm tall. It is a common and aggressive weed of lawns and turf that reproduces through seeds.
It is easily identified by its yellow-green color, boat-shaped leaf tips, and a distinct whitish flower head.
Poa annua Classification
- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Spermatophyta
- Subphylum: Angiospermae
- Class: Monocotyledonae
- Order: Poales
- Family: Poaceae
- Genus: Poa
- Species: Poa annua
- Varieties: Poa annua var. Annua and Poa annua var. reptans
- Common Names: Poa, Annual blue, Annual Meadow grass, Meadow grass, and Dwarf meadow grass
Nativity and Distribution
Annual bluegrass is native to Temperate Asia, Western Europe, and Northern Africa. Today it can be found in all ecosystems globally including:
- Australia
- Arctic
- Antarctica
- North America
- South America
Physical Characteristics
- Leaves: Smooth, yellowish to dark green, boat-shaped blades
- Stems: Upright, clump-forming stems about 30 cm long
- Flowers: White, stalked, awnless, spikelets 1-2 cm
- Roots: Fibrous roots system
Poa annua is primarily a winter annual grass, although in some habitats it can survive into the second year as a biennial.
It is easily identified by its clumping growth, smooth, yellowish to dark green leaves, and a distinct whitish flower head.
The stems are upright, clump-forming, and bright green, growing up to 2.5-30.5 cm tall. They enlarge by tillering and can root at the lower nodes.
The leaves are flat, smooth, 1-14 cm long and 0.25 cm wide, and often have a yellowish-green color with linear margins. They are typically transversely wrinkled and abruptly blunt at the tips, giving them a characteristic bow-shaped appearance.
Meadow grass produces greenish-white seed heads with spikelets 1-2 cm long. The spikelets contain 3-8 flowers each and are loosely arranged on spreading branches.
The seeds are long, elliptical, yellow-gray, about 0.25 cm long, and encased in a panicle.
Reproduction, Dispersal, and Life Cycle
- Life Cycle: Annual but can also be biennial
- Seeds: Each plant can produce over 2,000 seeds
- Climate: Cool, temperate climate
- Dispersal: Wind, water, animals, and contaminated seeds and vehicles
Annual bluegrass behaves as a short-lived winter annual but can also survive into the second year as a biennial. It typically thrives in cool temperate climates but is tolerant to a variety of soil conditions and hard frost, hence its existence in remote areas.
The grass is a prolific seed producer with a single plant producing between 1,000- 2,000 seeds. The seeds can remain dormant for many years in diverse ecosystems.
Poa annua is the only non-flowering plant to grow and maintain a seed bank in harsh territories like the Arctic and Antarctica.
The seeds are dispersed by wind, water, and animals, through contaminated seeds and farming equipment.
Similar Plants
- Poa compressa
- Poa pratensis
- Poa palustris
Uses
- It can be grown as livestock fodder in extremely poor grasslands.
- It is used as putting greens due to its high-traffic tolerance and low maintenance.
Impact on Farms and Environment
P. annua is considered an aggressive weed of various vegetables, cereals, and orchards in cooler climates. The grass itself has low competitive ability. However, due to its numerous seeds, it can rapidly colonize all available gaps in crop farms, causing poor plant management and harvesting difficulty.
Apart from competing for essential nutrients, the grass weed is also a host to cereal aphids and destructive weevils like the Sitobion avenae and Listronotus bonariensis respectively. These invasive insects often lead to poor crop yield and pasture quality and may require costly control measures to prevent large losses.
Annual meadow grass is a common and troublesome weed of lawns and turfgrass. To begin with, the grass is small in size and it is hardly noticeable as it grows along the desired turf.
Due to its unique yellowish-green color, it can make most turfs look patchy. Additionally, since it’s an annual, its tendency to die off can leave big bare patches on the turf depending on the size of the infestation.
Apart from crop farms and lawns, Poa annua is also a weed of roadsides, gardens, and waste areas.
Control
- Cultural control: Maintain a healthy and dense turf that can outcompete the grass weed.
- Mechanical control: Hand-pull or dig is a viable option for young plants.
- Chemical control: Apply herbicides like dithiopyr and pendimethalin
Maintaining a healthy and dense lawn is one of the best strategies to keep a Poa encroachment away. Applying the required nitrogen fertilizer and avoiding overwatering are some of the lawn maintenance measures that can help keep your turf grass vigorous and healthy.
If the infestation is small or the plants are young, you can hand-pull or dig using a tool to get the clumping weeds from the roots.
Poa annua is mainly controlled with preemergence herbicides like dithiopyr, oryzalin, and pendimethalin which are applied in mid-August to early September. However, it has been reported to become resistant to various herbicides like paraquat, glyphosate, and prodiamine when used for a long time.
We recommend consulting a local expert to find the best herbicide for annual bluegrass in your farm, orchard, garden, or lawn.
Lead Editor for Insight Weeds.