Knowledge Hub Article

Brome - Herbicide resistance

Herbicide resistance has not been detected so far in any UK brome species although two populations of sterile brome showing higher levels of tolerance 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. 

 

Control – herbicides
  • Pre-sowing – destroying all emerged brome plants before sowing a crop is essential.  Use of glyphosate can ensure a better degree of kill than cultivations alone.  Avoid cutting rates as this can lead to incomplete control and potentially increase the risk of resistance.
  • Pre-emergence herbicides alone (e.g. tri-allate, prosulfocarb, flufenacet,) will rarely give complete control so base herbicide control programmes on both pre- and post-emergence herbicides. 
  • 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, carbetamide 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.
  • Do not rely solely on herbicides – integrate their use with non-chemical methods.
Non-chemical control
  • 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.  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.
  • Increase seed rates to maximise crop competition.
Future issues
  • What is the relative frequency of the different species?
  • Herbicide-resistance in bromes – does it occur and, if so, how quickly will it increase?
  • The risk of glyphosate resistance in bromes
  • The relative response of different species and populations to herbicides – are any differences consistent?
  • Will there be any new herbicides?
  • Availability of herbicides – how many will we lose through EU and individual country’s regulatory decisions?
  • Non-chemical control measures – re-appraisal of their efficacy in relation to individual species.