Barren brome
Other names
Haver-grass, sterile brome
Latin names
Anisantha sterilis (L.) Nevski, (Bromus sterilis L.)
Weed Type
Annual Grass Weeds
Occurrence
Barren brome is a winter, rarely summer, annual grass, native in rough and waste ground, in hedgerows and by roadsides. It is a weed of arable land and gardens. Barren brome can spread from the hedge bottoms and field margins into the arable field where it may form dense patches. It is common throughout the UK. It is abundant on sands and other dry, freely-drained soils.
Since the mid 1970s it has increased as a problem weed in cultivated fields being favoured by the cultivation of continuous winter cereals and the adoption of non-ploughing techniques. In a survey of UK cereal field margins made as part of Countryside 2000, barren brome was one of the most frequent species recorded.
Biology
Barren brome flowers from May to July. Most flowers are self-pollinated but there is some cross pollination by the wind. A large mature plant may have up to 10 fertile tillers. Flower heads have 10-12 spikelets each containing 4-10 seeds. On average, over 200 seeds are produced per plant and a high proportion are viable. An isolated plant may produce up to 5,000 seeds. Seeds start to become viable 3-7 days after anthesis. Seed matures rapidly on the plant once ripening begins and most seed is shed from late June to early August.
There may be some initial dormancy but the majority of seeds will germinate immediately on contact with moist soil, especially if shallowly buried. Dry conditions will prevent germination. Sunlight can also inhibit germination and encourages the persistence of seed left on the soil surface. Autumn rains usually promote a flush of germination. Autumn is the main period for emergence but if dormancy is enforced by drought or low temperature, seed may persist through to the following spring.
Seedlings require a period of cold to vernalise them in order to flower. Spring emerging seedlings may not become vernalised and can fail to flower before crop harvest. The optimum depth for seedling emergence is quoted as 0-70 mm and the maximum is 130 mm. The greatest emergence is from depths of less than 50 mm and few seedlings emerge from deeper than 100 mm. No seedlings emerge from 150 mm.
Persistence and Spread
The majority of barren brome seed does not remain viable in soil for longer than 12 months and seed persistence is not generally a problem. However, seed that has become dormant after remaining on the soil surface may survive for an extended period. Although most seed is shed readily from the plant, the basal seed of each spikelet can remain attached to the flower stem until January. These seeds are slow to germinate and may represent an additional survival strategy for the plant.
In headlands, 99% of seed is dispersed within 1 m of the parent plant. Most of the seed is disseminated away from the hedge and towards the crop. Farming operations may carry the shed seed progressively further into the field. In the open field, seeds are dispersed up to 3.5 m from the parent plant. During cereal harvest, a combine harvester can carry barren brome seed up to 53 m in the forward direction, eject it up to 7 m backwards and scatter it up to 1 m on either side. Seed on plants near the headland would normally be moved parallel to the headland during combining rather than into the centre of the field.
Barren brome seed was an impurity in sainfoin, barley and wheat seed, particularly in home saved seed. Contamination was greatest in the seed of winter cereals. The drilling of contaminated crop seed can spread the weed much further afield. The awned seed caryopsis may also be carried on clothing and on animal fur. Apparently-viable seed has been found in horse-droppings.
Management
Only clean cereal seed should be sown and when barren brome is in the headland, care should be taken not to spread it into the field. The inclusion of spring-sown crops can help to break the cycle and reduce infestations. Growing spring barley is likely to reduce the weed unless a dry autumn has prevented germination, leaving the weed to emerge in the spring sown crop. In a moist autumn there may be an opportunity to kill barren brome seedlings if the winter cereal is not sown too early.
Seed persistence is not generally a problem when considering control measures. The majority of seed does not remain viable in soil for longer than a year. The burial of freshly shed seed avoids dormancy due to sunlight developing. Shallow cultivations encourage germination if the soil is moist. Seedlings are unable to emerge from below 130 mm so ploughing can be very effective if inversion is complete. Rotational ploughing, 1 year in 3, will normally keep moderate infestations in check. The stale-seedbed technique can also be effective in moist conditions but there is generally insufficient time between cereal crops to achieve this. Minimal tillage will encourage barren brome to increase in numbers.
In grassland, cutting should be done early enough to prevent barren brome seeding. In the headlands and field margins, barren brome must be cut down before the flower panicles develop but plants will re-tiller if cut too early. Competition from sown grass and wildflower mixtures suppresses the growth of barren brome. It is an aggressive species and can dominate sown grasses that emerge with it, however, it does not succeed in an established sward.
Arithmetical models have been developed that predict the emergence and growth of barren brome under different conditions. The models can be used to produce effective management practices including deriving economic thresholds for the different control options.