Dry conditions this autumn have led to variable effectiveness of pre-emergence herbicides with some growers opting to apply another residual herbicide at the one-leaf wheat crop stage.
Arable Alliance consultant Andrew Wells, who advises growers in the East Midlands, where conditions have been particularly dry, says: “Although growers have tried to delay drilling wheat, not enough have delayed long enough before they have drilled. There is quite a bit of black-grass coming through with the wheat and although, in most cases, it is not a carpet, there is perhaps more than they would really like to see, having spent money on residual products.”
Some growers are applying a further residual at the one-leaf crop stage, however, this could have crop safety consequences for following crops, he warns. “It is not an easy decision.”
There is the option of applying contact herbicides, however, there are resistance issues associated with these, says Mr Wells. “I’m not convinced they will add an awful lot.”
ADAS arable weed specialist Dr Sarah Cook says if it remains mild and black-grass is small, post-emergence herbicides should be applied. “The effects of enhanced metabolism resistance can be reduced by applications at these early growth stages when plants cannot metabolise the herbicide as effectively,” she says.
Mr Wells is more optimistic about crops which have only recently been drilled. “It has been cooler, with more moisture around and pre-ems should be more effective.”