Poa annua

Scientific name: Annual poa

(Poa annua) Poa annua

(Poa annua) Poa annua r

(Poa annua) Poa annua x
  • Key characteristics
  • Biology
  • Impacts
  • Control
  • Further information

  • A small but very common grass, growing mostly in winter, found in gardens, lawns, pastures, and on cultivated land
  • Leaf blades are hairless, bright green, with abruptly pointed or blunt hooded ‘canoe-like’ tips. These are 1.5-9 cm long and 3-4 mm wide, either folded or opened flat, weak, often crinkled when young, and with a characteristic square channel or ‘tramlines’ along the midrib
  • Flower stems are erect or lie along the ground, sometimes rooting at the nodes. They are very weak and slender, hairless, unbranched or sometimes branched at the base
  • Flower head is egg-shaped or triangular, usually open and loose, 2-10 cm long, pale to bright green, with reddish or purplish branches in pairs or solitary, spreading and hairless. Its spikelets are 4-6 mm long, with 3-6 light green or purplish flowers

    Considered an environmental weed by DOC. Care should be taken to prevent its spread in or near natural areas.

Origin

  • Originated in Europe, where it is still common in a range of habitats, especially those that offer bare soil and little competition from other plants
  • Introduced, presumably inadvertently, to New Zealand soon after European settlement began in the 1840s
  • Considered one of the most widely distributed plants in the world, and growing from seal level to above 2000 m in all continents. It is found in all parts of New Zealand.

Life cycle

  • Seeds can germinate at any time of the year in the presence of sufficient moisture, but in practice, germination most commonly takes place in autumn
  • The plants usually die out if the soil becomes dry, which usually happens in spring or early summer
  • Some forms of the plant can, however, act as perennials if soil moisture remains high throughout the year
  • The time lag between germination and setting seed is only about 5-6 weeks, and seed production is prolific
  • Seed can remain buried in the soil but still be viable for several years.

Benefits

  • The plant has moderate value for animal forage but produces little useful vegetation.

Impact on pasture

  • Although of very little value itself, Poa annua can take up pasture space better utilised by more productive grasses, especially during the winter months
  • Winter-growing Poa annua can alternate with summer grass (Digitaria sanguinalis) so that pasture production is lower both in summer and in winter
  • It can be a serious weed of new pasture as it germinates and grows faster than both perennial ryegrass and white clover.

Impact on livestock

  • Presence of this species in pastures reduces the contribution of more productive grasses to animal growth and health.

Pasture and turf management

  • Since Poa annua is itself a grass, controlling it in pasture or turf is difficult and is best managed by good cultural control
  • In pastures using appropriate pasture species, fertiliser and good grazing management is the best way of controlling this and other weed species
  • Keeping a dense sward of desirable species throughout the year is important for checking or preventing invasion by Poa annua
  • Increasing the sowing rate of ryegrass seed can help the pasture compete with this weed.

Chemical Control

  • Using herbicides for the selective control of Poa annua in pastures is not advisable
  • If pasture renewal is carried out, Poa annua is susceptible to herbicides like glyphosate, and along paths and in waste places Poa annua is susceptible to most commonly used herbicides
  • A summer cropping phase in pasture renewal may be required to reduce the amount of Poa annua seed in the soil
  • However, because this species has a short life cycle and produces very many seeds it can develop resistance to herbicides if similar herbicides are used regularly in the same place.
  • In fine turf – based on ryegrass – ethofumesate can give selective control of poa annua, but not if the turf includes fine fescues, couch or species of Agrostis. The herbicide pendimethalin gives fairly short term control of germinating seedlings of Poa annua.

Champion P, James T, Popay I, Ford K 2012. An illustrated guide to common grasses, sedges and rushes of New Zealand. New Zealand Plant Protection Society, Christchurch, New Zealand. 182 p.

Global Invasive Species Database, 2017. Poa annua (accessed 2 May 2017).

Harrington KE 2017. Poa annua. Massey University Weeds Database (accessed 2 May 2017).

Wardle DA, Barker GM, Nicholson KS, Addison PJ 1994. Cyclic oscillations between a summer-annual (C-4) and a winter-annual weed grass in Waikato dairy pastures. New Zealand Plant Protection, 47: 34-37.