United Kingdom
October 21, 2013
UK arable farmers who seized the opportunity to drill winter wheat early are likely to have to deal with an onslaught of black-grass that has germinated in crops, agronomy experts are warning.
As many as four key factors have combined to exacerbate black-grass problems this season, agree Syngenta field technical manager, Iain Hamilton, and southern counties independent agronomist, Richard Cromie of Crop Management Partners.
Even where pre-emergence herbicides have been applied, some large flushes of black-grass have still emerged, they point out. That places even greater emphasis on using an effective post-emergence treatment with a residual partner to target survivors, they add.
“Where wheat was drilled say before 25 September, we’ve seen a big autumn flush of black-grass,” says Iain Hamilton.
“A key factor that has contributed to this is the usual phenomenon of more black-grass germinating in early-drilled crops. But it has been compounded by low black-grass seed dormancy this year, and good seedbeds that have encouraged both crop and weed emergence. There was also a relatively dry period a few weeks ago in early-drilled crops, which may have hindered the activity of soil-applied herbicides to some degree.”
If growers are to maximise yield and reduce black-grass seed return this season, Mr Hamilton stresses it will be important to remove these surviving black-grass flushes before they reach the three leaf stage. Otherwise, he says, they can become extremely difficult to control.
“If the herbicide Defy, which contains prosulfocarb, hasn’t already been applied, then winter wheat growers should consider tank mixing this as a residual partner with their post-emergence mesosulfuron / iodosulfuron black-grass treatment,” says Mr Hamilton, “provided the crop and weed are at suitable growth stages.
“Trials have been conducted on this tank mix, and adding Defy to mesosulfuron / iodosulfuron has given an extra 10% black-grass control. Consider using Defy at 2 - 3 litres per hectare with mesosulfuron / iodosulfuron,” he suggests.
Richard Cromie agrees with the factors that have increased black-grass in early-drilled winter wheat crops this autumn.
“There have been some excellent seedbeds, no black-grass dormancy and the crop and grass weeds have grown quickly,” Mr Cromie explains.
“Some fields have had four active ingredients as a pre-emergence treatment and black-grass has still come through.”
Mr Cromie says his first post-emergence mesosulfuron / iodosulfuron applications are set to start in late October or early November on the earliest-drilled crops – some six weeks after pre-emergence herbicide application. “Which partner product you use depends largely on what you’ve put on already, but also, depending on your timing, on how much additional residual activity you want.
“The best partner I’ve found when there’s bigger black-grass has been a prosulfocarb product,” he adds.
“This year has emphasised the value of sterile seedbeds and delaying drilling for black-grass control,” Mr Cromie concludes.
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