Soil management plays major role in controlling black-grass

Appropriate soil management can play a major part in controlling your black-grass before it controls you, growers and agronomists were advised at the latest national Soil and Water Management Centre improvement event in Lincolnshire.

Speaking at the Seedbed Management Techniques Day, Agrii technical manager, David Langton said a strictly limited agrochemical arsenal, growing weed resistance and increasing climatic uncertainty made it vital to manage soils and tillage as effectively as possible to minimize the pressure on in-crop herbicides.

Drawing on the latest results from the company’s long-term system trials on fields with serious multiple herbicide resistance near Huntingdon, he highlighted cultivation flexibility, multiple stale seedbeds and delayed drilling as particular opportunities for tackling problem fields.

He said: “We’ve conducted carefully controlled trials on the same challenging heavy land fields at Stow Longa for more than 10 years now. Not surprisingly with a marsh weed like black-grass, these have shown that rectifying drainage issues and cultivating to facilitate water infiltration are key areas for improvement.

"In our latest trials with Lemken, ploughing stood out as the best way of reducing black-grass in a single season, giving us nearly 100 per cent control in our 2010/11 wheat through effective seed burial. Indeed, with 100 black-grass ears/sq.m taking almost exactly 1t/ha off wheat yields, we recorded a net benefit of £100/ha over our shallow min till regimes after accounting for the extra £45/ha cost.

"It’s important to stress, though, that ploughing needs to consistently bury the seed below 3” in the profile. And ploughing two years in a row can lead to greater problems by bringing up non-dormant black-grass seed buried the previous year.  Ploughing after direct drilling wheat the year before, for instance, resulted in an average of just six black-grass plants/sq.m  in our OSR compared to 123 plants/sq.m from ploughing after ploughing.”

Good stale seedbeds plus the cheapest available black-grass herbicide – glyphosate – were essential, said Mr Langton. “This can eliminate up to 90 per cent of the season’s potential black-grass population. But it must be done correctly and is dependent on sufficient soil moisture.

"The fact that early germinating black-grass can suppress the germination of other black-grass seed means two cycles of two stale seedbed treatment in a row tend to be better than one, although it’s important to appreciate that not all glyphosates allow this on the label.

"Under these circumstances, delaying the drilling of the worst black-grass fields to give time for repeated pre-planting control can be enormously beneficial wherever conditions allow. As, of course, is a robust pre-em programme in wheat, wherever possible, and effective propyzamide/carbetamide treatment in OSR.”