Tackling sterile brome through integrated weed management
With high seedbank populations, sterile brome is a persistent weed. Teagasc researcher Vijaya Bhaskar outlines some of the integrated weed management (IWM) options to prevent the weed from growing into yield-robbing infestations.
In Ireland, there are five different brome types: 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 (headland meeting main field) can result in brome appearance in ploughed fields.
In the UK, the economic threshold for sterile brome is just five plants/m2. Unmanaged brome can directly decrease yields, cause lodging, contaminate grain, increase control costs, and return an incredible number of seeds to the soil seedbank to reinfect your land.
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 areas:
Pre-harvest decision:
- Looking for flowering heads and accurate weed identification (main picture);
- Marking/mapping the weed patches and inspect field margins;
- Never miss an opportunity to stop seed set (eg. hand rougeing for small infestations, spray off distinct patches, etc.).
Decision at harvest:
- Machine hygiene (before coming into fields as well as before moving from field-to-field), and harvesting fields with high weed pressure last to stop seed spread.
Post-harvest control measures:
- Single or multiple stale seedbed: Shallow cultivation (max 5cm depth) immediately after harvest will result in higher germination of freshly-shed seeds and the opportunity to spray off with glyphosate or to cultivate again. 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.
- Delayed drilling: Delayed autumn-drilling of winter cereals until the second half of October to avoid the main autumn flush.
- Cultivation systems: 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. 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.
- Field margin management: 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.
- Herbicide options: In winter wheat or winter barley, residual herbicides applied as pre-/early post-emergence based on flufenacet-based mixtures (eg. Firebird Met) will offer limited 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.
In the below video, Vijaya Bhaskar gives an overview of his work in Teagasc and how are we going to control weeds in the future with an even smaller armoury of herbicides and herbicide resistance increasing:
If brome levels are higher than would be controlled by any of the above measures then more long-term actions are required which may include:
- Change rotation to give more control options
- Good – oilseed rape, beans, beet, maize; Moderate: winter wheat, winter rye; Poor – winter oats, winter barley (avoid).
- For example, using winter oilseed rape allows the use of early post-emergence propyzamide (eg. Kerb Flo) in sequence with spring post-emergence herbicides (eg. Centurion Max, Falcon, Stratos Ultra).
- Incorporate spring crops or an entire spring rotation to reduce the challenge.
- Switch to a plough-based tillage system in conjunction with the above.
In the below video, Charlotte Morgan, a PhD student based at Oak Park, outlines her research activities and discusses what she will be presenting at next week's Crops and Cover Crop Cultivations open day.
Adopting these measures in conjunction with stale seedbeds and meticulous attention to detail may allow a brome ‘reset’. This may allow a return to non-inversion tillage and more winter cropping, but very tight brome management would need to be incorporated to reduce the need for, or time to, another ‘reset’.
If you suspect herbicide resistance, you can send your population for resistance testing to Teagasc Oak Park to know effective herbicide options. Contact your advisor or follow instructions on https://bit.ly/3MrlcgR
Photo caption: Dropping sterile brome seed heads visible above barley crop. Distinct feature: the main axisof panicle is hairless or only minutely hairy. Ligule is medium (2-4mm) and serrated. Leaves rolled within stem.
Crops and Cover Crop Cultivations open day
The Teagasc Crops and Cover Crop Cultivations Open Day takes place Wednesday, 21st June, 10am to 5pm in Teagasc Oak Park, Carlow. This event brings the Oak Park Crop Research Programme to the public, supported by researchers, PhD students and advisors.
For more information on this event, click here.