blubber grass, lop-grass, soft chess
Bromus hordeaceus L. (B. mollis)
Soft brome is a tufted annual, sometimes biennial grass native in waste places, meadows and on dunes. It is common throughout the UK and is recorded up to 1,800 ft. Soft brome occurs in a range of grassy and open habitats, mostly managed by man. It is common in pasture and in the verges alongside paths. Soft brome is now frequent on arable land and is becoming more of a weed problem.
In a survey of cereal weeds in central southern England in 1981-2, soft brome was found in 1% of winter wheat fields but was not recorded in winter or spring barley. In a survey of the incidence of Bromus spp. in winter cereals in mainland Britain in 1989, soft brome occurred in almost 10% of fields.
Soft brome varies both genotypically and phenotypically. Four subspecies have been recognised in the UK, 3 native and 1 introduced.
The Seed Act required dealers to declare the presence of seed of this grass in seed offered for sale if it exceeded 1% in clovers and 2% in grasses. The sale or use of seed containing more than 5% of weed seed is illegal.
The flower heads appear from May to July and seed is set from May to early August. The flowers are wind pollinated. Plants cut down when flowering do not ripen seed but plants cut at the milk stage produce seeds with over 80% germination. Fully ripe seed gives up to 96% germination. There is no effect of light quality on germination but germination decreases at low temperatures. There is a high level of germination in the dark but seed from different populations has demonstrated some inhibition in the light, however, most gave 39 to 85% germination in the light.
Seeds germinate in spring and autumn. Seed sown in July in pots of soil outdoors and stirred periodically emerged almost completely in the month it was sown and the following 2 months. No further seedlings emerged. Over 90% of seed mixed in soil in the field and stirred periodically emerged within 12 months.
Soft brome becomes established and grows very quickly. It remains green through the winter but vegetative growth occurs mainly in the autumn and spring.
Soft brome seeds have minimal dormancy and are short-lived in soil. Seed buried in mineral soil and left undisturbed retained up to 11% viability after 1 year but none was viable after 4 years. Seed buried in a peat soil at 26 cm was not viable after a year. Seed stored under granary conditions demonstrated 30% viability after 1 year but none was viable after 4 years.
In clover and grass seed samples tested in Denmark for the period 1966-69, 1955-57, 1939 and 1927-28, soft brome seed was a contaminant in 13.7, 7.5, 8.9 and 14.4% of samples respectively. Soft brome has been found as an impurity in sainfoin seed.
In grassland, mow hay early and cut pastures at the beginning of June to prevent soft brome seeding.
Soft brome sheds its seeds in early summer and the weed can become a problem in succeeding cereal crops. Seed is best left on the soil surface for as long as possible after shedding to encourage predation. Any remaining seed should be ploughed at least 15 cm deep. The drilling of winter cereals should be delayed to encourage a flush of soft brome seedlings to emerge and be controlled. The inclusion of spring crops will help to eradicate the weed.
Updated October 2007.