Refining spring cropping approaches for blackgrass control

Article taken from Farmers Guardian, September 2017.

Spring drilling on heavy land can help control black-grass, according to the latest results from Agrovista's Project Lamport site in Northamptonshire.

For the past four seasons, an ear­ly autumn-sown cover crop based on black oats, followed by spring wheat, has achieved the best black­grass control at the site, where un­treated populations of the resistant weed reach 2,000 plants/sq.m.

The cover crop is combi-drilled after a light discing. This, together with the slow early growth of black oats, encourages black-grass to chit and establish well.

The cover crop then bulks up, conditioning and draining the heavy soil over winter. It and the black-grass are destroyed with two sequential applications of glyphos­ate before drilling.

Profitable

This has allowed a profitable spring cereal to be established on poten­tially difficult clay soils over a series of very different seasons, while driving down black-grass numbers in crops and reducing the soil seed bank, says Agrovista technical manager Stewart Woodhead.

He says: ""The key is to move the soil to maximise black-grass ger­mination when we establish the cover crop, but to minimise soil movement in spring when estab­lishing the wheat crop to minimise the chances of a spring flush.""

In 2017 spring wheat, KWS Willow, was sown at 500 seeds/sq.m on March 28 with a Great Plains Saxon direct drill to keep soil movement to a minimum.

However, using discs-only on a Vaderstad drill or similar can produce a similar low-disturbance performance, says Mr Woodhead.

""Seed rate is key- we only expect 40-60 per cent germination in this land, and crop competition is important-black-grass will quickly fill any gaps.""

Attention to detail is key when drilling - the operator must be on board with the process, says Mr Woodhead.

""You need to check tractor tyre pressure and travel at the appropri­ate speed and direction to reduce unnecessary soil movement.""

Glyphosate

Destroying the cover crop with glyphosate around Christmas, rath­er than a couple of weeks before drilling, appears to be the optimum timing in year two onwards. This avoids leaving excess debris which traps too much moisture in the top couple of centimetres of soil.

Under this regime yields hit 8.65t/ha (3.5t/acre) last season, while profits neared £1,000/ha (£404.85/acre), allowing for the cost of cover crop seed and with wheat priced at £135/t. The black­grass count was reduced to just 1.4 plants/sq.m. Mr Woodhead expects a similar performance this season.

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 black-grass, despite a full herbicide programme costing about £150/ha (£60.72/acre ).

""Four years after using the plough and throwing the best chemistry we have at it, the plot still contains about 500 heads/ sq.m," says Mr Woodhead.

""We are expecting this wheat to yield in the region of 5-7t/ha, which will lose money.""