Cover Crop + Direct Drilled Spring Wheat = Best Blackgrass Control

Article taken from Farm Contractor  & Large Scale Farmer, September 2017.

For the fourth season running, the best control at Lamport, where untreated resistant blackgrass populations exceed 2000/m2, has been achieved by using the correct cover crop in tandem with direct-drilled spring wheat.

The aim is to establish a low­-biomass cover crop, based on black oats, in early autumn, sown with a combi-drill after a light discing. This maximises blackgrass germination and establishment, before the cover crop bulks up to condition and drain heavy soils over winter. It is then burnt off, along with the blackgrass, ahead of the spring wheat.

This system has enabled a profitable spring wheat crop to be established on potentially difficult clay soils over a series of very different seasons, while driving down blackgrass numbers in crops and reducing the soil seed bank, according to Agrovista technical manager Stewart Woodhead.

"It is well documented that spring drilling is key to controlling grass weeds. The challenge is to spring drill consistently well," says Mr Woodhead. "The key is to move the soil to maximise blackgrass germination when we establish the cover crop so we 'capture' it and kill as much as possible when the cover crop is burnt off.

"We then want to minimise soil movement when establishing the wheat crop to minimise the chances of a spring flush. The last thing we want to do is select for spring germination - we are effectively limited to an annual meadow grass type of spray programme in spring cereals, so most of the effect is coming from cultural control."

The spring wheat, KWS Willow, was sown at 500 seeds/m2 on 28 March with a Great Plains Saxon direct drill, although observations elsewhere on the site suggest a Vaderstad drill or similar used with its legs removed can produce a similar low-disturbance performance, says Mr Woodhead.

"Seed rate is key - we only expect 40-60% germination in this land, and blackgrass will quickly fill any gaps."

Attention to detail is essential when drilling - the operator must be fully on board with the process, he says. "You need to check tractor tyre pressure and travel at the appropriate speed and direction to reduce unnecessary soil movement."

Last year the spring wheat achieved almost St/ha under this system, and profits topped £900/ha. The blackgrass count was just 8.4 heads/ha.

By contrast, the standard farm practice plot (two winter wheats followed by oilseed rape) of first wheat, combi-drilled at the end of September, is inundated with blackgrass, despite a full herbicide programme costing around £150/ha.

"Four years after using the plough and throwing the best chemistry we have at it, the plot still contains about 500 heads/m2," says Mr Woodhead. "We are expecting this wheat to yield in the region of 5-7t/ha, which will lose money."

It is all too easy to undo all this good work by reverting to winter cropping too soon, especially on a high blackgrass site such as Lamport, Mr Woodhead warns. "In autumn 2015, one plot was put back into winter wheat after two years of overwintered cover crop/spring wheat which was a massive mistake - we got an enormous chit of blackgrass."

The cover crop/spring wheat sequence was re-introduced this season but has had to be sprayed off due to the blackgrass pressure.

"The question now is how can this be controlled," says Mr Woodhead.

"We played our trump card with the plough when we established Project Lamport in 2012. Back then, only about 40% control was being achieved with a full herbicide programme.

Even after four seasons there will still be plenty of viable blackgrass seed below the surface, so we certainly don't want to plough that up again.

"It can take a number of years to reduce this seed bank to manageable levels even without returning blackgrass seed to the soil, which means several seasons of at least 98% control."

The trials also show that Agrovista's spring cropping system outperforms the more common practice of spring cropping after a stale seedbed fallow (see table 1 ).

"Using a cover crop helps bind the soil together, improving the benefits of no-till. Omitting it means there is nothing to help soil structure - apart from producing poorer yields and profits, opting for an over­wintered fallow failed to achieve consistent blackgrass control in the following wheat crop," says Mr Woodhead. "The soil is moved too much and shattered, allowing blackgrass to chit, returning more than six times as much seed to the soil, which is allowing the population to increase."

Destroying the cover crop with glyphosate around Christmas appears to be the optimum timing, rather than a couple of weeks before drilling, which can leave excess debris that traps too much moisture in the top inch or two of soil. The cover crop still has time to develop enough root to condition, dry and stabilise the soil ahead of sowing.

Under this regime yields and profits have risen substantially compared with early spring destruction, while the blackgrass count dropped sharply.

Key principles

• Choose the right cover crop for the job
• Drill correctly for minimal soil disturbance in the spring
• Attention to detail



04 September 2017

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