Poa annua

Scientific Name	Poa annua L.
Common Names	English: Annual bluegrass; German: Einjähriges Rispengras; French: Pâturin annuel; Spanish: Espiguilla, poa anual
Description	P. annua is an annual grass, which may persist as a short-lived perennial depending on habitat, climate and management. It is a weakly competitive weed with rapid flowering and profuse seedling.

Characteristic Features

Leaves are often transversely wrinkled with characteristic tramlines.

Young Plant

Tufted, 5 - 30 cm (1.97 - 11.81 inch) high, root at the nodes, youngest leaf folded.

Stems

Erect, in the vegetative state geniculate. Flowering culms are erect and smooth 10 - 30 cm (3.93 - 11.81 inch) tall, without hairs.

Leaves

Leaves flat, slightly keeled with characteristic 'tramlines'; smooth and abruptly contracted at the apices
('boat-shaped tip'). Transversely wrinkled.
Ligule membranous and typically 2-3(-5) mm (0.078 - 0.118 - 0.197 inch) long, often truncate or acute.
No auricles.
Sheath is smooth, keeled and somewhat compressed.

Flowers

Culms with open triangular or ovate panicles, 2-12 cm (0.78 - 4.72 inch) long, solitary or paired branches.
Spikelets 3-10 mm (0.12 - 0.39 inch) long, lanceolate with 3-10 florets.
Glumes boat shaped, acute apex, lower glumes 1.5-3 mm (0.059 - 0.12 inch) long, 1 vein, upper ones 2-4 mm (0.078 - 0.16 inch) long with 3 veins.
No awns.

Flowering Period

Spring through autumn.

Fruit

Caryopsis develops in summer.

Seeds

Germination nearly all year round.

Viability of Seeds

Typically short-lived (2 - 5 years), but when moderately dormant considerable presence in the soil seed bank may result and emergence over consecutive years can be expected.

Propagation

By seeds.
150 to 1,000 seeds per plant.

Habitat

P. annua is a cosmopolitan grass, highly successful in occupying niches to avoid competition with dominant plants.

Soil

Annual bluegrass tolerates a range of soil conditions, but prefers fertile agricultural soils with an adequate water supply. The plant tolerates moderate to hard frost.

Additional Crop Information

Short straw cereal varieties offer favorable conditions for P.annua, which also is frequently found in vegetable crops, turf grass and plantation crops.

Agricultural Importance

P. annua is ubiquitously distributed and widely adapted to diverse habitats but has a relatively low competitive ability. It survives as a weed because of its high genotypic and phenotypic variability, rapid germination and tolerance to compacted soils. It is a major weed in turfgrass.

Useful non-chemical contribution to Integrated Weed Management

Annual bluegrass can be suppressed by dense and fast growing crops. Deep soil tillage in winter results in seed mortality due to fatal germination.