- Sterile brome in wheat 002 1024x700
Biology and Impact
In the UK, there are five main species which frequently occur as weeds of arable crops. Their relative frequencies, as reported in the Atlas of the British Flora (2002), are given as the (%) of the 2852 10 x 10 km grid squares surveyed in which the species was detected.
Bromus sterilis – sterile or barren brome. Very common throughout England and Wales, more scattered in Scotland. (65%). Very common in field margins and hedgerows as well as within arable fields.
Bromus diandrus – great brome. Mainly recorded in East Anglia but scattered throughout the rest of England. (11%). Probably under-recorded due to confusion with B. sterilis.
Bromus hordeaceus – soft brome. Very common throughout the UK. (85%). Most commonly found in grassland, field margins, waste ground and roadside verges, but does occur in arable fields too.
Bromus commutatus – meadow brome. Mainly recorded in the southern half of England. (27%). More commonly found in grassland situations, especially old pastures, but also occurs in arable fields.
Bromus secalinus – rye brome. Mainly recorded at scattered locations in the southern half of England. (14%). Largely confined to arable fields, field margins and waste ground. Probably under-recorded due to confusion with B. commutatus.
Why does identification of species matter?
- Different control measures apply to sterile and great compared with soft, meadow and rye brome in relation to post-harvest cultivations.
- Label claims for control of bromes vary so knowing which species is present can help in herbicide decision-making, although there are also non-label claim for control.
- Great brome is generally considered a more challenging species to control than sterile brome, requiring more robust strategies
- Meadow brome tends to be better controlled by mesosulfuon+iodosulfuron than rye brome.
Damage: bromes are some of the most competitive grass-weed species with similar competitive abilities to wild-oats and Italian rye-grass. A population of five plants/m2 typically causes a yield loss of 5% in cereals, but much higher crop losses can occur in severe infestations, especially if crop lodging occurs. High populations can slow harvesting and lead to contamination of grain and straw. All brome species are greatly encouraged by non-inversion tillage and early sowing.
Seeds of all brome species tend to have shorter dormancy, and be less persistent in the soil, than black-grass, rye-grass and wild-oats. Annual seed decline in the soil is about 85 – 90% for bromes as compared with 70 – 80 % for black-grass. Consequently, preventing seed production should enable brome populations to be substantially reduced within two years, but achieving complete control can be a challenge. Soft, meadow and rye brome seeds have slightly greater longevity in the soil than sterile and great brome.
- Do not rely solely on herbicides – integrate their use with non-chemical methods.
- Prevent importation and spread of seeds – many infestations (especially of sterile and soft brome) originate from field margins so active headland management can prevent further ingress.
- Avoid moving seeds from field margins into the main body of the field in combine harvesters or cultivation equipment and avoid introduction of seed in contaminated crop seed, straw or manure. Brome seeds are unlikely to survive anaerobic digestion (AD), although this needs verification.
- Rogue plants, or spray off patches, in May/early June wherever possible, especially on headlands.
- Map brome patches in June/July. Identify species present and plan management accordingly.
- The best post-harvest cultivation strategies differ between species
- with sterile and great brome, shallow cultivation immediately after harvest is beneficial as it encourages germination. (If seeds are left on the surface, exposure to light induces dormancy and hence delays germination).
- with meadow, rye and soft brome, shallow cultivation immediately after harvest is detrimental as it enforces dormancy and increases seed survival. It is preferable to leave seeds to ripen on the soil surface for about one month before cultivating.
- Ploughing, at least on a rotational basis, can be very effective at reducing brome populations. Good inversion is needed as brome seeds can emerge from greater depths (10 cm) than black-grass or rye-grass (5 cm). Ploughing the perimeter of fields can help prevent ingress but achieving good inversion here is often difficult.
- Delayed autumn sowing can be particularly beneficial, especially if several weed flushes can be achieved and seedlings destroyed effectively with cultivations or glyphosate. Glyphosate used alone at the rate usually recommended for annual grass-weed control on stubbles (540 g a.i./ha) is sometimes only partially effective on bromes, especially in marginal conditions. Failure to kill brome seedlings pre-drilling may results in re-emergence of these plants post-drilling.
- Spring cropping can greatly reduce brome populations, although it is important that all emerged plants are destroyed pre-drilling.
- Base herbicide control programmes on both pre- and post-emergence herbicides. Pre-emergence herbicides alone (e.g. triallate, prosulfocarb, flufenacet,) will rarely give complete control.
- Post-emergence herbicides for use in winter wheat (e.g. pyroxsulam mixtures, mesosulfuron+iodosulfuron, propoxycarbazone, sulfosulfuron) are all ALS inhibitors and can only be applied once in any programme. Label claims for control of different brome species vary between products, but some also have non-label claims too. There are no effective post-emergence herbicides for controlling brome in winter or spring barley.
- Inclusion of non-cereal break crops enables the use of a wider range of herbicides, including propaquizafop, quizalofop, cycloxydim, clethodim and propyzamide which can all be used in oilseed rape. Note specific recommendations for use in other crops.
- Apply post-emergence herbicides according to label recommendations. Be aware that the ideal timing for brome control may conflict with the best timing for control of other grass-weeds, such as black-grass and wild-oats.
- Increase seed rates to maximise crop competition.
No herbicide-resistant brome species have been detected in the UK so far although two populations of sterile brome showing very marginal resistance to glyphosate have been found in Leicestershire and Oxfordshire. Populations of sterile brome resistant to ACCase and ALS inhibitors have been found in France and Germany and resistance in great brome and rye brome has been recorded in other parts of the world. Hence, herbicide resistance in brome species is a potential threat in the UK. Seed or plant samples from fields where resistance is suspected should be collected and tested in standard assays.