Focus on soil management for blackgrass control
Appropriate soil management can play a major part in controlling your blackgrass 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 recent Seed-bed Management Techniques Day, Agrii technical manager David Langton warned that a strictly limited chemical arsenal, growing weed resistance and increasing climatic uncertainty make it vital to manage soils and tillage as effectively as possible to minimise the pressure on in-crop herbicides.
Armed with 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 seed-beds and delayed drilling as particular opportunities for tackling problem fields.
“We’ve conducted carefully controlled trials on the same challenging heavy land fields at Stow Longa for more than 10 years now,” he explained. “Not surprisingly, with a marsh weed like blackgrass, 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 to reducing blackgrass in a single season, giving us nearly 100% control in our 2010/11 wheat through effective seed burial. Indeed, with 100 blackgrass 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 3in in the profile. And ploughing two years in a row can lead to greater problems by bringing up non-dormant blackgrass seed buried the previous year. Ploughing after direct drilling wheat the year before, for instance, resulted in an average of just six blackgrass plants/sq m in our oilseed rape compared with 123 plants/sq m from ploughing after ploughing.”
On this evidence, rotational ploughing certainly looks to be a better bet than a complete return to the plough. Careful ploughing about once every three years – when time and conditions allow – is suggested as the best option for badly-infested ground.
Where ploughing is not a viable option, extensive studies at Agrii farm trial sites with particular grassweed problems show some reduced tillage regimes can be almost as effective at controlling blackgrass, while generating higher margins over establishment and chemical costs; providing they are accompanied by effective stale seed-beds.
“Good stale seed-beds plus the cheapest available blackgrass herbicide – glyphosate – are essential here,” Mr Langton insisted. “This can eliminate up to 90% of the season’s potential blackgrass population. But it must be done correctly and is dependent on sufficient soil moisture.
“The fact that early-germinating blackgrass can suppress the germination of other blackgrass seed means two cycles of two stale seed-bed 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 blackgrass fields to give time for repeated pre-planting control can be enormously beneficial wherever conditions allow. As, of course, is a robust pre-emergence programme in wheat, wherever possible, and effective propizamide/carbetamide treatment in OSR.
“If we are to rise to a blackgrass challenge which is just as great for many today as it was before the advent of Atlantis, we really need to know our weed,” Mr Langton concluded. “As well as its resistance status, we should identify where it is, both in the field and in the soil profile. That way we can use the tillage and other soil management tools at our disposal in the most cost-effective, integrated control approaches.”
