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Multiple herbicide actives required to power-up brome control

With brome infestations becoming more widespread, and ALS resistance confirmed in UK populations, cereal growers will need to use a selection of herbicide active ingredients to achieve acceptable levels of weed control this autumn.

Whilst classified as a very competitive weed, brome has largely been confined to field margins, with any seeds that migrated into fields traditionally prevented from germinating by the burying action of ploughing. However, the increasing popularity of min-till and no-till establishment systems – as a cheaper, more soil-friendly alternative to ploughing – has resulted in increased brome populations within cereal and oilseed rape crops. 

This poses a significant threat to crop viability, not just because their vigorous growth habit means brome species can cause yield reductions on a par with black-grass and ryegrass (a population of five plants/m2 typically causes a yield loss of 5% in cereals), but because resistance to ALS-inhibiting herbicides has already been confirmed in UK brome populations.

Growers must therefore use a robust sequence of pre- and post-emergence herbicides to ensure adequate levels of control are achieved. That’s according to Dr Bill Lankford, Herbicides Technical Specialist for ADAMA UK, who explains that a range of active ingredients and application timings is required to provide full control of the UK’s five main brome species*. 

“New box trials carried out on behalf of ADAMA have shown that TOWER® (40 g/l diflufenican, 300 g/l pendimethalin and 250 g/l chlorotoluron) is not only effective against troublesome annual meadow grass and broad-leaved weeds, but also offers useful activity against sterile, meadow and rye brome,” Dr Lankford explains. “It also provides good activity as a partner product in ryegrass and groundsel control programmes.”

The independent trials, carried out by ADAS, indicated that the efficacy of TOWER® varies according to target species and timing of application, with each species of brome responding differently.

“As a result, instead of taking a ‘carte blanche’ or farm-wide approach to brome control, growers must understand exactly which species they are tackling before tailoring their weed control programme to match the growth stage of crops and germination phase of weeds on a field-by-field basis,” Dr Lankford recommends.

For example, rye and sterile brome were shown to be the most susceptible to TOWER® when applied at the pre-emergence or early post-emergence (GS11-13) timings, while meadow brome is only susceptible to TOWER® when it is applied in combination with diflufenican at the pre-emergence timing, or when applied with prosulfocarb from pre-emergence through to tillering (GS21). The addition of prosulfocarb was also shown to improve control at all timings for all species of brome.

Dr Lankford’s core message is that growers can no longer rely solely on post-emergence ALS treatments to clean-up crops in the spring. “Instead, agronomists and growers should also use early post-emergence treatments to extend the residual life of pre-emergence applications,” he explains.

“The trial results indicate a clear difference in terms of the performance of different active ingredients when applied to brome which has germinated from a controlled depth, at the same time and with sufficient moisture, but these conditions are not the same as those found in field situations,” Dr Lankford continues. “Practical brome control programmes therefore need to consider the biology of the field population and the sensitivity of that population to herbicides, particularly ALS inhibitors to which there is already some known resistance.”

Additional trial work has also shown that FALCON® (100g/l propaquizafop) provides excellent protection against four of the brome species, giving a 92-98% reduction in target populations of ALS resistant barren, great, meadow and rye brome.

“FALCON® is the leading herbicide for the control of volunteer cereals in broad-leaved crops,” Dr Lankford explains, “but can also be used as part of an IPM approach for brome reduction in winter oilseed rape and other broad-leaved crops.

“We also found that cycloxidim works well in controlling ALS resistant species of brome in oilseed rape, with an application of FALCON® to control volunteer cereals and a subsequent treatment using cycloxydim to tackle later emerging grassweeds the recommended way of controlling brome species as they emerge throughout the autumn. This gives OSR growers the option to target subsequent flushes of brome with different active ingredients than those used in their autumn cereal herbicide stack.”