Part article taken from Crop Production Magazine, September 2017, written by Lucy de la Pasture.
When it comes to blackgrass control, every little bit helps. Competition between the crop and weeds is a two-way process, but tipping the balance in favour of the crop will help suppress blackgrass, says Dr Stephen Moss. The big question is how much can you do to help influence this?
""There's a lot of mumbo-jumbo associated with cover crops but they have the potential to offer lots of value in blackgrass situations, in an indirect way," believes Stephen.
Agrovista's Stewart Woodhead agrees, adding that cover crop is a misnomer and should really be called a trap-crop where blackgrass is concerned.
""In our view, a cover crop isn't there to out-compete blackgrass. The last thing we want is to shift the germination of the weed to the spring by selecting for spring-germinating types of blackgrass. The aim of an autumn cover crop is to trick the blackgrass into germinating by planting into shallow cultivated soil, where only the top 5cm has been disturbed," he says.
Stewart believes the best cover crop in a blackgrass situation is one with a low biomass in the autumn and drilled at a low seed rate, so that there's plenty of space for the blackgrass to emerge. The initial concept behind planting a cover crop was to reliably enable spring drilling on heavy land because a spring crop is more able to reduce blackgrass populations, he explains.
Soil workability
""The cover crop biomass helps remove water from the soil while binding the soil together, meaning soils can be worked earlier in the spring. Where fields have been left over-winter as a stale seedbed, soils are normally dry on the top but wet underneath. For cover crops, this is often the other way around but there's still an improvement in the earliness the soil becomes workable," he explains.
At Lamport, Agrovista's heavy-land blackgrass site in Northants, four year's work on cover crops and companion crops has shown some promising results in a background blackgrass population of over 2000heads/m2 ""A cover crop followed by spring wheat has given at least 98% control for the past three years. It's important not to look at any one year in isolation when it comes to blackgrass, different strategies and types of cover crop will be appropriate for different fields in different years.
""Spring wheat following black oats and vetch has consistently performed well at Lamport. The project was originally intended to be a five-year project but it's been extended because five years won't be long enough to bring blackgrass back down to manageable levels," he says.
Stewart believes that there's been far too much reliance on chemistry to solve the blackgrass problem and it should be considered as a last resort.
""We need a change of mindset and cultural strategies in place even before blackgrass becomes a substantial problem on the farm. On top of that, attention to detail is most important.
When direct drilling into a cover crop, all the good work can be undone by drilling too fast and creating soil disturbance, enabling a new flush of blackgrass to come through,"
he comments.
Stephen agrees, adding that cover crops aren't a magic solution but part of a much bigger picture when it comes to influencing blackgrass populations.