Sequence or Stack Strategy for Grass Weed Control
12 September 2024, UK: After the disastrous 2023/24 season for grass weed control, that has set-back programmes by up to a decade in many fields, it will be more important than ever to adopt the right strategies and optimise the herbicide application to get back on track.
Drilling date for this season’s autumn crops will have major implications for tackling grass weeds – including decisions on adopting a stacked or sequenced herbicide strategy with DEFY to get back in control, advises Syngenta Technical Manager and grass weed specialist, Georgina Young.
With many fields suffering an immense burden of grass weeds after last year’s challenging conditions, delayed drilling could be highly beneficial to clean up seedbeds.
However, repeated bad experiences of difficult autumn establishment is likely to see a preference to get crops in the ground and away when conditions allow.
Coupled with more farmers’ commitment to faster and more cost-effective min till or direct drill establishment, the appetite to plough down and bury the seed burden could be limited.
Stale seedbeds
Conditions for stale seedbeds have been good this season, with some soil moisture and warmth. Although an initial light scratch of surface cultivation, to encourage weeds to chit, does add time and cost, if the first soil movement is the drill pass that will likely trigger a big flush of weeds just as the crop is emerging.
Syngenta grass weed research has demonstrated the benefit of early shallow cultivation of a stale seedbed, which reduced subsequent black grass seed head numbers by 15% compared to a later min-till pass, along with 5% fewer than direct drill establishment.
Black-grass dormancy
Furthermore, weather conditions during black-grass seed set in the summer indicated high levels of seed dormancy.
That means more of the grass weeds will escape the initial seedbed clean up, and we are likely to see a prolonged germination of weeds emerging through the autumn, exacerbating the issue in earlier drilled crops.
For these fields a sequenced approach with a strong pre-emergence treatment, followed by a later post emergence application, will provide the necessary longer activity against germinating grass weeds.
Including DEFY in the grassweed strategy gives growers the immense flexibility to typically use it in wheat with recommendations in stronger mixes up to 3.0 l/ha at pre-em for black-grass or 5.0 l/ha targeting ryegrass, or at up to 2.0 l/ha in the follow-up post-em sequence.
In a high dormancy season, such as this year, trials applying a pre-em of DEFY, Crystal and DFF, followed in sequence with a post-em at GS11, increased black grass control by 27%, compared to a pre-em application alone.
Sequencing herbicide applications, with pre-em and peri-em treatments, has also been shown to increase ryegrass control.
Single-shot pre-em
Where farmers can select fields suitable to delay drilling, the weed burden should be lower. Combined with the risk of poor weather or soil conditions limiting follow-up spray applications, a switch to a robust stacked pre-em strategy becomes the appropriate approach.
The key to success with the single-shot pre-em strategy is providing sufficient herbicide activity to control later emerging weeds. Syngenta trials have shown in low pressure or later drilled fields DEFY can be highly effectively incorporated into pre-em stacks for both black-grass and ryegrass situations.
Grass weed research over the past 15 years has consistently shown increasing the number of active ingredients in the stack, along with using increased rates of DEFY, improves the reliability and levels of black-grass control.
Strong stacks of reliable, well-proven products, including higher rates of DEFY, have shown to give highly cost-effective grass weed control at least as good as newer chemistry introduced in the past few years.
Supported mixtures
The new list of DEFY supported mixtures and recommendations of use for the 2024 autumn season are now available quickly and conveniently in the field on the Syngenta MyField app.
Application Advice
Discover the power of precision with the Syngenta Spray Assist app, your go-to digital tool for spray operators.
Customizable to fit your farm’s unique equipment, this app harnesses high-definition weather data to pinpoint the perfect spray times. It also suggests the ideal nozzle combinations and application techniques for outstanding results in both pre- and post-emergence applications. Stay ahead with real-time weather forecasts and alerts for changing conditions, ensuring your operations are always on track. Best of all, Spray Assist is free to download.
Recommendations are designed to reinforce the advice on forward speed, boom height and water volume, to achieve maximum spray deposition on the soil surface and consistent coverage to achieve the best possible results – Go Low; Go Slow; Get Covered!
Poor application can reduce grass weed control by up to 50%.
However, paying attention to maintain boom height at 50 cm, to operate at less than 12 km/hr and apply at a water volume of 200 l/ha, using drift reducing 3D ninety technology nozzles, will each incrementally improve results.
Although spraying at 12 km/hr and applying 200 l/ha does take longer, trials have shown an 8-10% improvement in weed control, compared to application at 100 l/ha.
MyField
The Spray Assist app dovetails into the Syngenta MyField digital farm set-up. MyField is a comprehensive app that puts essential decision-making tools, product support and Syngenta rewards into the palm of your hand, simply download myFIELD and register to start receiving weather warning risks for your area.
Add in your fields, using the integrated Google maps tool, and get BYDV forecasting tailored precisely to your location and crops, as well as all Syngenta’s product information and labels.
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