According to Teagasc research scientist Vijaya Bhaskar, there are five different brome types in Ireland, of direct interest to farmers: Sterile; great; soft; rye; and meadow.
Of these, sterile brome is the most widespread. It typically encroaches from the field margins to headlands and then the main field body.
Poorly inverted soil can result in brome appearance in ploughed fields.
In the UK, the economic threshold for sterile brome is just five plants/m2.
Management of sterile brome
Unmanaged brome can directly decrease yields, cause lodging, contaminate grain, increase control costs, and return an incredible number of seeds to the soil seed bank to re-infect land.
The clear advice from Teagasc is that it is now time to plan integrated weed management (IWM) strategies, which are largely based on cultural and judicious herbicide use, to tackle the brome problem.
Decisions are needed in three key areas.
Pre-harvest, growers should be looking for flowering heads and making accurate weed identification. The marking or mapping of weed patches is also important. Field margins should also be inspected.
In addition, growers should never miss an opportunity to stop seed set i.e., hand-rouging small infestations and spraying-off distinct patches.
Machine hygiene
Machine hygiene is critically important during harvest. Fields with high levels of weed infestation should be harvested last.
There are a number of post-harvest control measures that can be taken.
Shallow cultivation (max 5cm depth) immediately after harvest will result in higher germination of freshly shed seeds.
Thereafter, the opportunity to spray off these plants with glyphosate or to cultivate again will present itself.
Multiple stale seed beds can have an additive effect, provided there is time to do it.
In other situations, a chopped straw cover spread evenly may provide adequate darkness and moisture to trigger rapid germination of brome seeds.
The delayed autumn drilling of winter cereals beyond the mid-point of October means that a new crop is going into the ground at a date beyond the main germination flush of brome seeds.
Ploughing to a depth of 15cm or more can bury seeds below emergence depth and, unlike other weeds, repeated ploughing may carry less risk of viable brome seeds to resurface.
Bromes are more difficult to control in non-inversion systems.
Cultivation
Shallow cultivation to establish a stale seedbed can be very useful in direct drill or strip-till situations. In deep non-inversion tillage, the weed seeds are distributed through the soil profile to the depth of cultivation.
This may bury seed and add these seeds to the seed bank rather than reducing their numbers through immediate germination.
Where field margins are concerned, establishing a perennial cover or grass margin will provide competition to slow the growth of brome from headland and reduce seed return.
Such field margins should be mown in the following May and September to encourage grass tillering and prevent seed return.
In winter wheat or winter barley, residual herbicides based on flufenacet-based mixtures will offer limited brome control.
The only products that offer effective control can only be used on winter wheat (eg., Pacifica, Monolith, Broadway Star) need to be applied at full recommended field rates, when conditions are optimum in terms of weed and crop growth stage and temperature/weather.
Unfortunately the continued use of these chemistries (particularly if used at rates lower than the recommended) does risk resistance development or less-sensitivity in bromes and other grass weeds.