Arable weeds: Basic black-grass biology

Integrated control strategies require a good understanding of black-grass weed biology. Find out more about the life cycle of this key arable weed to help you beat it.
How to manage black-grass in arable crops The encyclopaedia of arable weeds

Where is black-grass found?

Geographic location

Distributed all over the British Isles, black-grass (Alopecurus myosuroides) is most abundant in cultivated land in South-East England. However, it has gradually spread North and West, recently arriving in South-East Scotland and Northumberland. It remains rare in northern Scotland.

Soil type

Black-grass is found on heavy and light soils, but thrives on heavy, poorly drained soils.

What does black-grass look like?

This annual grass weed has upright, round and slender stems with few nodes. The young leaves are fine and smooth with a shiny upper surface. The leaf blade is twisted with a blunt tip. The lower sheath of larger seedlings is often purple. Black-grass grows in graceful tufts. The very narrow, dark purple flowerhead is packed with single-flowered spikelets. It can reach up to up to 85 cm in height.

Various growth stages of the arable weed black-grass


Black-grass can be confused with loose silky-bent at the young plant stage of development. This is due to the reddish/purple colouring of the leaf sheath; however, silky-bent tends to prefer lighter soils.

Basic black-grass biology

  • Seeds produced in high numbers
  • Seeds shed before crop harvest
  • Average seed decline in the soil is 75% per year
  • Seed dormancy and soil moisture/temperature affect emergence patterns
  • Low dormancy occurs in warm, dry conditions
  • Seeds often grow rapidly (providing moisture is not limiting)
  • Most black-grass emerges from seeds within 5 cm of the soil surface
  • Most plants (about 80%) emerge in early autumn
  • Black-grass can continue to emerge from clods broken down during winter
  • There is very little spring emergence from undisturbed soils
  • In some years, black-grass germinates as the crop ripens
  • Plants tiller in early spring

Life cycle

Basic black-grass life cycle

Black-grass seed statistics

  • Seed longevity: 1–5 years
  • Seed decline: 80% per year
  • Germination depth: 5.7 cm
  • Seed weight: 1.8 mg
  • Seeds/head: 100
  • Seeds/plant: 800

Further information

How to manage black-grass in arable crops The encyclopaedia of arable weeds Managing weeds in arable rotations – a guide