Battle against brome requires multi-pronged approach

• Problem weed now in more fields

• Herbicide resistance is challenge

• Range of options required to win

Cereal growers are being reminded to use a selection of herbicide active ingredients when tackling brome this autumn.

Although classified as a  competitive weed, brome has until now been largely confined to field margins, with any seeds that migrated into fields prevented from germinating by the burying action of ploughing.

So far, so good. But the increasing popularity of min-till and no-till establishment as a cheaper and more soil-friendly alternative to ploughing has resulted in more brome in cereals and oilseed rape.  This poses a significant threat to crop viability.

A vigorous growth habit means just five brome plants per square metre can cause a 5% yield loss in cereals – similar to blackgrass and ryegrass. A nd herbicide resistance means a range of options should be considered when tackling the weed.

Full control

A robust sequence of pre- and post-emergence sprays is needed to ensure adequate levels of control are achieved, says herbicide expert Bill Lankford, of Adama UK. A range of active ingredients and timings is required to provide full control of the UK’s five main brome species, he adds.

Independent trials carried out by Adas suggest the efficacy of Tower (40 g/l diflufenican, 300 g/l pendimethalin and 250 g/l chlorotoluron) varies according to target species and timing of application, with each species of brome responding differently, says Dr Lankford.

Herbicide Tower  is not only effective against troublesome annual meadow grass and broad-leaved weeds, but also offers useful activity against sterile, meadow and rye brome, he adds. “It also provides good activity as a partner product in ryegrass and groundsel control programmes.”.

Field-by-field approach

“Instead of 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.”

Rye and sterile brome are most susceptible to Tower when applied at pre- or early post-emergence (GS11-13) timings, suggest the Adas findings. But meadow brome is only susceptible when applied with diflufenican at pre-emergence, or with prosulfocarb from pre-emergence to tillering.

The addition of prosulfocarb was also shown to improve control at all timings for all species of brome.

Residual life

This all means growers and agronomists should no longer rely solely on post-emergence ALS treatments to clean-up crops in the spring. Instead, they should also use early post-emergence treatments to extend the residual life of pre-emergence sprays.

“The trials indicate a clear difference in 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.

“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.”

Four species

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 – and it can also be used as part of an integrated pest approach for brome reduction in winter oilseed rape and other broad-leaved crops,” says Dr Lankford.

“We also found that cycloxidim works well to control ALS-resistant brome species in oilseed rape, with an application of Falcon to control volunteer cereals and a subsequent treatment using cycloxydim to tackle later emerging grassweeds [including brome] throughout the autumn.

“This gives oilseed rape growers the option to target subsequent flushes of brome with different active ingredients than those used in their autumn cereal herbicide stack.”