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.
Where is black-grass found?
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.
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.
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
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