Constructing blackgrass herbicide programmes on the basis of final control levels alone may actually lose growers both yield and money, according to trials carried out last season by agchem distributor Agrovista.

In the trials an autumn application of Atlantis yielded 0.4t/ha more than a spring application, despite 97% control from the latter programme compared with 92% for the autumn programme (see graph), says the firm’s technical manager Mark Hemmant.

Both programmes started with a pre-emergence treatment of Trooper + trifluralin + Grounded, while an IPU holding spray was applied before the spring Atlantis treatment.

“That type of result shows constructing a herbicide programme on the basis of the final level of control alone needs to be re-examined.

Growers need to consider the impact of early removal of blackgrass on yield and margin.”

Other plots in the trial confirmed early removal of blackgrass was key to getting the best yields, he says.

“Research suggests weeds emerging with the crop are up to 10 times more competitive than later emerging weeds, which probably explains why the programmes giving the best control of blackgrass in the autumn had the best yields.”

Using a good pre-emergence treatment, such as Trooper + trifluralin + Grounded is an essential part of the programme to get the best autumn control, he says.

“There was a 0.4t/ha penalty for not applying a pre-emergence prior to the IPU/spring Atlantis treatment, as well as a 7% loss in control.

Our trials have consistently shown the benefit of that treatment over cheaper alternatives.

“Given the good seed-bed conditions and plenty of soil moisture this season, it should work particularly well,” he suggests.

Whether the pre-emergence should be followed by Atlantis in the autumn or a holding spray before spring application will depend on the season, he says.

“If blackgrass germination is complete and the weather conducive, applying Atlantis plus a residual partner in the autumn will be appropriate.

“If Atlantis is delayed until the spring, then growers should ensure the autumn programme will achieve good control of blackgrass to avoid losing out on yield,” he concludes.

mike.abram@rbi.co.uk