English ryegrass, ray-grass
Lolium perenne L.
Perennial Grass Weeds
Perennial rye-grass is a tufted, fibrous rooted perennial grass that is generally regarded as native and is common throughout Britain. The wide distribution may be a result of the once exclusive use of perennial rye-grass in the sowing of leys. It has been in cultivation as a forage grass since the 17th century. As a consequence of seed spread during transport of hay from the fields it became established along trackways and roads. Perennial rye-grass prefers fertile soils and is rare in upland pastures unless lime has been applied. It is at its best in old swards, on rich soil, under summer grazing management.
The earliest cultivars flower in May but flowering of different cultivars continues throughout the summer. Flowers are wind pollinated, with the pollen travelling up to 180 m. Flowers are self-incompatible. Limited self-pollination can occur but the progeny exhibit low vigour. High levels of nitrogen reduce the number of spikelets per inflorescence and hence the number of seeds but this is offset by an increased number of inflorescences. Seeds ripen within 4-5 weeks of flowering.
Persistence and Spread
Plant longevity is variable both between and within populations and ranges from annual or biennial to extremely persistent. British cultivars grow well under cool moist conditions but are not the most winter hardy. Excessive autumn growth reduces tillering and the ability of a plant to survive a severe winter. If such plants are cut back hard they are unlikely to regenerate. In pasture, perennial rye-grass does not persist and re-sowing or sward renewal is required periodically.
Seed is the primary form of perpetuation but the seed is relatively heavy and natural dispersal is limited. Seeds of perennial rye-grass have minimal dormancy and are short-lived in soil. Seed remained viable for up to 7 years in dry storage but in soil all the seeds may germinate within a year. The length of persistence of buried seed depends on the cultivar, frequency of cultivation, soil type and burial depth. Seeds of different cultivars buried at 13 cm in undisturbed mineral soil retained 4 to 22% viability after 4 years. Seed buried in a peat soil at 26 cm retained 9% viability after just 1 year.
In roadside verges, more frequent cutting increased the incidence of perennial rye-grass. Perennial rye-grass also benefits from grazing and becomes much more aggressive under heavy grazing. It is also tolerant of trampling. In permanent grassland, high nitrogen levels favour perennial rye-grass. It is also positively associated with the presence of white clover.
In greenhouse tests in the USA, corn gluten meal (CGM) applied as a surface and incorporated treatment to soil has been shown to reduce plant development in perennial rye-grass. Corn gluten hydrolysate (CGH), a water soluble material derived from CGM, was found to be more active than CGM when applied to the surface of pots of soil sown with perennial rye-grass seed.
Perennial rye-grass seeds in soil are killed by steaming at 75°C.
The root feeding larvae of the cranefly (Tipula paludosa), a pest of grassland, graze the roots of perennial rye-grass. However, this stimulates the growth of the grass perhaps because the roots that regrow are finer and more efficient. Root-grazed rye-grass plants were more competitive against broad-leaved dock (Rumex obtusifolius).
Updated October 2007.