Post-harvest stubble management systems can be used to get on top of many herbicide-resistant grassweeds.
It is part of an integrated pest management (IPM) approach to the control of weeds. Stubble management is also inextricably linked to the new nitrates regulations.
Teagasc specialist, Shay Phelan has said: “There has been a significant increase in the cases of problem grassweeds like bromes, wild oats and blackgrass being reported to Teagasc advisors again in 2023.
“Stubble cultivations are the first step in the control of many grassweeds as the reliance on herbicides is not achieving adequate control on many farms.
“As part of the IPMworks project, we visited Denmark in June, where Italian ryegrass has become a bigger problem than blackgrass on many farms.
“Where the problem is bad, growers are spending up to €15/ac on various herbicides trying to control grassweeds, on top of all the IPM measures available.
“Herbicide resistance is widespread, as Italian ryegrass has the ability to develop resistance even faster than blackgrass.”
Stubble management
Teagasc has already received samples to Oak Park, Co. Carlow of both Italian ryegrass and blackgrass from growers in Ireland, which are resistant to many of the common herbicides.
“In Denmark, a full IPM approach including crop rotation, rogueing, stubble cultivations, machinery hygiene, herbicides and possibly grass ley are being considered to eliminate the problem, as using herbicides alone was not the answer,” Phelan continued.
According to Phelan, shallow cultivations, no deeper that 2cm, will encourage up to 80-90% of sterile brome and blackgrass seeds to germinate.
But growers should be careful not to cultivate too deeply as this can induce dormancy in some weed seeds and delay germination until next season.
Recent surveys carried out by Teagasc have confirmed the scale of the growing challenge posed by herbicide-resistant grassweeds to Irish tillage farmers.
Moreover, this is a problem that will escalate dramatically, if the required preventative steps are not taken now.
A case in point, blackgrass counts of up to 400 plants/m² were recorded in parts of England earlier this year.
The Nitrates Directive is designed to prevent pollution of surface waters and groundwater from agricultural sources and to protect and improve water quality.
As a consequence, tillage farmers are now required to take measures to establish green cover as soon as possible post-harvest to prevent the pollution of waters caused by nitrates.