A key role in tackling blackgrass

Article taken from Farmers Weekly magazine

Cover crops have an important role in tackling herbicide-resistant blackgrass by improving soil conditions to enable direct drilling of spring wheat on heavy land.  Results from trials in Agrovista’s Project Lamport, in Northamptonshire, shows a spring wheat based system can successfully bring heavily infested blackgrass heavy land back into productivity.  The combination of spring cropping and cover cropping resulted in a viable crop of spring wheat, which last summer yielded more than 10t/ha.
Blackgrass counts were just four heads/sq m, in the same field where untreated areas had more than 2000 heads/sq m.

The system
Stewart Woodhead, technical manager at Agrovista, looked at work done by blackgrass guru Stephen Moss showing that spring cropping is the best cultural approach to reduce the grass weed.
“But drilling on heavy soil in spring can be a real challenge.  So how can you increase success using cover crops?” asks Mr Woodhead.  French researchers have worked on this problem and Agrovista looked across the channel for some solutions using cover crops to control blackgrass.
“But unlike the French system, we are not looking to smother blackgrass, we want it to germinate in autumn.
“This is achieved by drilling at a lower seed rate,” he says.
However, he has made sure there is enough cover crop to get moisture extraction in winter, thereby providing well drained soil for direct drilling in the spring.

The cover crop
So what makes the ideal cover crop? It has to be easy to establish, not compromise yields, not create a new volunteer weed problems, not harbour pests and diseases and be easy to kill, says Mr Woodhead.  The carbon to nitrogen ratio is also important as it allows nutrients to be returned, and they have developed two specific mixes – black oat/vetch and black oat/berseem clover.
He warns that not all black oats are the same.  “We use a later maturing variety (Avena strigosa) to avoid seeing seed heads in the autumn and creating a new volunteer problem.”
The cover crop is drilled, ideally in late August, and by drilling at a low seed rate, the creation of the seed bed will allow and encourage blackgrass germination.
“We did try phacelia, but it smothered the blackgrass and once it was killed in spring, we saw blackgrass spring up and there was no reduction in blackgrass numbers the following year,” he says.
Another learning point was to tweak seed rates where there are high residual nitrogen levels, such as when following oilseed rape, to allow blackgrass germination.
Niall Atkinson, national trials co-ordinator, says some growers have adopted the system and seen disappointing results.  He says these growers were starting with a very high blackgrass population, and he advised them to plough the land first and bury the seed.
“It has to be proper ploughing to get numbers down and this is not easy on strong land,” he says. 

Spring establishment
One important factor when establishing the spring wheat is two strikes with glyphosate.  The first application goes on two weeks before drilling the crop, followed by a second hit two days before drilling, to hit blackgrass hiding under the cover crop.  Mr Atkinson says growers should not hear drills bunging up when direct drilling, as the extensive root structure means plants are well anchored and the drill just runs through.
“The roots also reduce soil disturbance.  Stale seed beds tend to be dry on top and you see more soil fracturing when direct drilling, therefore, you see more blackgrass germinating in the spring,” he says.