Stubble to stubble grass weed control

02 August 2022, UK: Extreme dry weather could compromise efforts for grass weed control in stubbles across the eastern counties this season, while welcome rainfall in western regions offers the valuable chance to tackle difficult ryegrass populations.

Adapting post-harvest cultivations and crop establishment systems to target specific grass weed populations can have a huge impact on weed pressure in the autumn, as well as optimising the results of Defy pre-emergence herbicide programmes, advocates Syngenta Technical Manager, Pete Hawkins.

“Grass weeds have to be considered at virtually every stage of the crops agronomy, from stubble to stubble,” he advised.

“While most elements of an integrated strategy have a general benefit for all grass weeds, there are some strategies that can be best used where specific species are the primary target.”      

For ryegrasses and black-grass in particular, once the season’s crop has been harvested Syngenta trials have shown the benefit of shallow stubble cultivations to encourage germination, he urged. But If conditions are too dry and unlikely to produce a seed chit, then avoid cultivations.

“With bromes, however, some species, including meadow, rye and soft brome, are best left on the soil surface for up to a month to encourage germination. Earlier cultivations will delay the breaking of dormancy in these species.

With other brome species, such as sterile (Barren) and great brome, immediate shallow soil disturbance can encourage rapid germination.”

Pete is mindful that growers will be highly conscious of cultivation costs this season, especially with the high cost of fuel and machinery parts, along with labour availability for stubble work.  

“Adapting your stubble cultivations, and subsequent crop establishment techniques, remains highly valuable and cost effective as part of the overall weed control strategy,” he pointed out.

A 30% reduction in the weed seed bank with a stale seedbed would make a big contribution in terms of overall weed control.

“Reducing grass weed populations prior to drilling could facilitate the use of lower cost shallow or min-till establishment systems for more seasons, before the need for rotational ploughing to bury any build-up of seeds at the top of the soil profile,” he added.

Syngenta grass weed research has repeatedly shown rotational ploughing, once every four to five years, has proven the most effective strategy in high black grass and ryegrass situations, reported Pete.

The new Cultivation Insight app on the Syngenta website provides an easy-to-use guide of where grass weed seeds will end up over successive seasons, with any combination of establishment techniques.

“Based on years of research at the Barton Black-grass Innovation Centre, near Cambridge, it calculates where weeds seeds will move in the profile and the potential viability of emergece in the autumn.

“Growers and agronomists can use the information to assess likely impacts of what has happened in fields in previous seasons, as well as the implication of adopting any chosen establishment system for this year, or future seasons.”

He believes the Cultivation Insight could prove extremely useful for planning the optimum approach for each field across the farm, to make best use of available options and maximise the grass weed control through cultivations and establishment.

“The Syngenta five-year Sustainable Farming project has consistently shown the greatest financial returns have come from direct drill establishment, albeit at a yield penalty, compared to plough-based establishment.

“However, when the weed burden gets too high, our grass weed research shows the plough is the best way to reset the situation.

“The Cultivation Insight app can help to work out just when and where it can be best utilised to reduce grass weeds in the autumn.”

Targeting grass weeds in the autumn, through a combination of cultural controls, delayed drilling and Defy pre-emergence herbicide treatments, will maximise control of the most competitive early emerging weeds.

“That’s crucial to achieve the highest possible yields from this season’s crop, as well as the most sustainable long-term management of grass weed populations,” Pete advised.                

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