Arable

Survey highlights extent of UK-wide brome problem Meadow brome is one of the five species of brome found in the UK.

A four-year project investigating the extent of brome on arable farms in the UK is also focusing on the weed’s potential for herbicide resistance. Dominic Kilburn writes. Results of a survey carried out last year on the extent of brome present on UK farms has revealed that the weed species is more widespread on cereal growing land than previously thought. In addition, 59 per cent of respondents suggested that brome was becoming an increasing problem on their farms. Speaking at the AHDB Agronomists’ conference at the end of 2017, ADAS weed researcher Dr Laura Davies (right) outlined that the survey was part of an ADAS-led AHDB-funded project investigating the distribution and presence of brome in the UK, as well as identifying the potential for herbicide resistance among the species. Partners in the four-year project, which started in March 2017, include BASF, Bayer, Dow AgroSciences, Monsanto, UPL and Rothamsted Research. According to AHDB, bromes are highly competitive weeds with infestations of sterile brome at densities of 5 plants/m2 causing up to a 5 per cent yield loss. Herbicide resistant brome populations have been found in other parts of the world but not in the UK as yet, however lessons learned from black-grass herbicide resistance build up means that careful attention needs to be paid to other high risk grass weeds, warned the AHDB.

Survey The project got underway with a survey last summer to identify the 8

main species being found on UK farms and where they were occurring. “The last time a survey was carried out relating to brome in the UK was in 1989, so it was clear that we didn’t have any up-to-date information, and, while we expected responses to highlight most populations of brome to be in the North West, West and Scotland, we actually found there was a wide presence of brome in the South and South East too,” explained Dr Davies. “Brome weeds are present across the whole of the UK’s cereal growing regions,” she added. According to the survey of 200 growers, sterile brome was the most abundant species of the five found in the UK. “That said, we also had 58 samples of brome sent in for herbicide sensitivity testing of which 38 per cent were identified as the wrong brome species,” Dr Davies continued. “It may, or may not, be important to get the identification of bromes right but part of the project is looking to see if different species are more or less sensitive to herbicides, and therefore whether growers and agronomists need to know what they are dealing with down to an individual species level,” she pointed out. Dr Davies added that the best time to identify brome species was at flowering and seed shedding when the difference between the species was most easily defined. For more help with identification, the ‘Which brome is that?’ guide can also be viewed on the Crop Protection

website, she said. With 59 per cent of responses claiming that brome was becoming a worse problem on farm, Dr Davies suggested that the move to min-till and no-till on many arable farms as part of a strategy to reduce the incidence of black-grass, could inadvertently increase populations of sterile and great brome. “In addition, some growers have moved away from certain herbicide actives due to resistance problems with black-grass, without realising that they were getting incidental grass weed control with them,” she commented. On the flip side, a lot of those who thought they had seen a decrease in brome populations on their farms cited better crop rotations, more spring cropping, good use of herbicides and better cultivations as the reason. The survey also highlighted the worrying trend that as well as brome being found in its traditional field margin and headland locations, the vast majority of those surveyed said it was appearing in the centre of fields. This is an increasing problem, stressed Dr Davies.

Resistance As many as 59 growers surveyed suspected they had brome on their farms which was resistant to herbicide; ALS and ACCase chemistry getting most of the blame. “We still have no confirmation of brome resistance to herbicides in the UK and it could well have been poor herbicide application at the time that caused the lower levels of control, but the number of suspected cases is worrying,” she suggested. The results of the survey, alongside experimental work examining herbicide sensitivity, will

be used to map brome population changes and update best practice weed management guidelines for brome in the future. Glasshouse and laboratory tests began last autumn testing populations of sterile, rye, meadow and great brome for resistance to ALS herbicides, with early results showing that ALS-treated sterile brome showed the greatest variation in the level of control achieved. “Some populations were less well controlled than others and so the question is that if I took those less well controlled populations and started doing different control methods with them, would I get resistance?,” said Dr Davies. “That’s something I’ll be looking at in the future,” she added. “There was less variation in the control of great and meadow brome and so this points to the fact that we may need to identify which species we have in the field as some are harder to control than others,” she explained, adding that growers should always use the full recommended rates when tackling brome with herbicides. This spring, populations of brome will be tested for sensitivity to ACCase, fops and dims and glyphosate herbicides. “As well as developing an integrated brome management plan for the future, a big part of the project is focusing on herbicide resistance testing, and so any growers who have a sample of brome that they think is resistant to a herbicide, can send it in to ADAS to be tested for free. “There’s no brome resistance reported in the UK as yet but there is the potential for it and we don’t want to get into a situation like black-grass. “We want to be proactive about preventing resistance rather than having to control it once it has evolved,” she concluded. ■

In the past, brome was typically found at field margins and on headlands (above) but the survey suggested that it is increasingly being found in the centre of fields too.

www.farmersguide.co.uk February 2018

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