Agronomists and farmers have reported notably higher brome populations in cereal fields across some UK regions in recent seasons. Martin Rickatson finds out more.
There may be many bromes, but for the purposes of control of the weed – which some suggest has become more prevalent since the advent of managed field margins and wider adoption of min-till – they are not all alike. Knowing which of the two distinct species groups is present in a problem area is the key to effective control.
That’s the emphasis from researchers, weed scientists and agronomists when questioned on the subject of what can be done to tackle a brome problem, after a succession of recent years during which field reports of issues with the weed increased markedly.
NIAB TAG’s John Cussans points out bromes haven’t been alone among weeds in benefiting from the lack of decent frosts in recent winters, but suggests their distinctive appearance, particularly when concentrated in patches, has made them particularly more noticeable. The weather has aided their growth, but other practises have helped their spread, he says.
“Bromes sit between blackgrass and wild oats in terms of their effect on cereal yields, with barren/sterile brome having the most significant impact, at 2.4 per cent winter wheat yield loss where there are three plants/sq m. But, of course, there are also the other problems they can cause, such as lodging and combining difficulties.
“Bromes aren’t classic weeds of typical arable situations, being typically more commonly found in field margins and uncropped areas such as beneath pylons. But the introduction of field margin schemes has aided brome establishment in some cases, particularly where the margin seed mix hasn’t established well. Manage margin areas with the same attention to detail as the crop in the body of the field, ensuring good seed mix establishment and growth, and this weed seed source will be minimised. ”
The other key aid to the propagation of bromes has been the move to minimum tillage, suggests Mr Cussans.
“Ploughing obviously buries shed seed deep, from where it cannot emerge – although barren brome, for example, does have a seed longevity of 1-5 years. No-till, on the other hand, leaves it on the field surface, where it is exposed and ripens. But min-till of the top few cm of soil buries it just deep enough to invoke dormancy and create problems later.”
Preventing spread is a matter of managing field boundaries to ensure they are distinct and clean, ensuring cultivation close to field boundaries does not drag out and disperse weed material, and properly establishing any margins with their intended species.
“Brome species identification, though, is critical to pre-drilling control of a problem already established in the body of a field,” stresses Mr Cussans.
“The classic spiky bromes, sterile/barren brome and great brome – the anisantha species – are best dealt with as soon as possible after harvest, as exposure to light induces dormancy. Bury through ploughing or, if min-tilling, shallow cultivation to create a weed flush before glyphosate application.
“Bromus types – meadow, soft and rye bromes – are more typically species of field edges, with seeds ripening later than sterile brome and great brome. Burying them straight after harvest will therefore induce dormancy, aid survival and lead to later emergence in the crop. The approach here should therefore be to leave the shed seed on the field to allow it to mature for a month, before cultivating shallowly and spraying off.”
Sarah Cook of ADAS points out that brome is often an incidentally-controlled weed, knocked back as a result of aiming primarily at other target grassweeds such as blackgrass.
“This has meant that, as problems have developed in achieving good control of these primary targets with post-emergence ALS herbicides, and fewer are being used, then poorer control of brome has also become more evident,” she explains.
“The AHDB Information Sheet 31, or the more recent ‘Identification of brome grasses’ written by Dr Stephen Moss, can help with the identification of the different brome species, and therefore the correct control approach to take. Once the seed heads are visible in June-July, identification is easier. The key difference is that the anisantha species have long awns and loose, floppy flowering heads, while the bromus types have short awns and neater heads.”
Dr Cook warns against being complacent if using mowing to deal with problem patches on field boundaries, in margins or under pylons.
“This must be done before the panicles begin to emerge as viable seed is produced soon after flowering. But the same plant can head again, so it’s necessary to observe the mown area for some time afterwards to address this if it happens.”
Brome species of all types appear to favour the light, chalky soils that make up much of the land overseen by Hampshire-based independent AICC agronomist Seumas Foster, who reports seeing a shift in types in recent years.
He says: “The predominant type here used to be sterile brome, but now we’re seeing more great, rye and meadow bromes. Great brome in particular can be an issue – one or two plants often creep into field areas unseen or are mistaken for wild oats, and once they have shed seed the population explodes. In addition, there have been some cases where herbicide control has not been great, with the weed appearing dead and then beginning to grow away again a few weeks later.
“The wider adoption of min-till has almost certainly helped create problems by developing seed dormancy in shallowly-buried seed that then chits later on in the next crop.”
Some farmer clients are reintroducing the plough as a 4-5 year rotational grassweed control tool, he says, with knock-on benefits for brome control aside from the main target weeds. In terms of other elements of cultural control, as well as echoing advice on correctly-timed mowing, he urges farmers not to cultivate too closely to hedges or field margins, and to ensure that sprayed-off separation strips are sufficiently wide to prevent seed shedding from hedge/margin-residing brome.
“If it is established in the crop, then early control in autumn using Broadway Star (pyroxsulam + florasulam) is the best measure, to tackle the weeds when small. There is always the risk of a later flush, and if necessary then Pacifica (mesosulfuron-methyl + iodosulfuron-methyl-sodium) is a spring control option.”
Great and sterile brome species can be the most difficult to eradicate, so a robust autumn spray programme is required, believes Stuart Jackson of Dow AgroSciences.
“They are more effectively controlled when small, at weed growth stage 11-13, and actively growing. Autumn spray programmes should include a pre-emergence spray such as 4.0 l/ha Crystal (flufenacet + pendimethalin) soon after drilling, followed by an appropriate post-emergence contact graminicide such as Broadway Star (pyroxsulam + florasulam) with adjuvant, and a residual partner such as Stomp Aqua (pendimethalin).”
Timing post-emergence sprays to control meadow, soft and rye bromes can be more flexible, he suggests. Autumn treatment off the back of a pre-emergence foundation to the programme still provides the best results, though.
“A post-emergence application of Broadway Star can be applied in autumn, but can be delayed until early spring if necessary.”
Devon farmer and contractor James Lee, who farms 300ha of sandy soils, has been successfully direct drilling with a Claydon machine since 2007. Sterile brome, though, has been one weed that, in some fields at least, occasionally rears its head.
Centurion Max applied Saturday. Already starting to work on the brome and ryegrass and black grass not looking happy pic.twitter.com/EtvFrPY6Z4— David Lines (@LinesDavid)
“After a spring tine pass to stimulate weed growth before spraying off, my aim is to move as little soil as possible when drilling,” he explains.
“That works very well in keeping grassweed burdens down, but brome has been a puzzle for a year or two now in some small areas. Even in adjacent fields under the same rotation, some develop bad patches while others have none. It’s not a significant problem but we know development is a risk, so we farm using a rotation and practices that bear this in mind. Dealing with weed issues like this was one reason I volunteered to be the AHDB Monitor Farm for this region.”
To tackle it, he is taking a largely cultural approach, to supplement a herbicide programme based on Broadway Star and Pacifica.
“Our farm is a mixed unit with beef and sheep, and we’re using rotational grass as one control measure. Adding further crops in a broader rotation is also helping. We’re growing wheat, maize, barley, some linseed, and had been growing winter beans, but as an open crop with few grassweed herbicide options, they can provide an environment for brome development. That’s one reason I’m dropping our bean acreage and putting in oilseed rape next year.
“We’re also taking extra care near field boundaries to avoid dragging seed out into the field, and drilling the headlands last. Ensuring both combine and baler are properly cleaned down after working in fields where brome is present is also hopefully helping to contain any spread of the weed.”