Project Lamport leads fight against resistant blackgrass

Article taken from Anglia Farmer, October 2017.

Spring drilling on heavy land can help control blackgrass - but reverting to winter cropping too soon can quickly undo the good work, according to the latest trial results from Agrovista.

An early autumn-sown cover crop based on black oats, followed by spring wheat, has achieved the best blackgrass control for the past four seasons at Agrovista's Project Lamport site in Northamptonshire.

Untreated populations of resistant blackgrass at the site can reach 2000 plants/m2. The cover crop is combi-drilled after a light discing. This, together with the slow early growth of black oats, encourages blackgrass to chit and establish well.

The cover crop then bulks up, conditioning and draining the heavy soil over winter. Both it and the blackgrass are then de­stroyed with two sequential app­lications of glyphosate before drilling.

This has allowed allows a prof­itable spring cereal 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, says Agrovista technical manager Stewart Woodhead.

No spring flush

"The key is to move the soil to maximise blackgrass 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."

Spring wheat KWS Willow, was sown at 500 seeds/m2 on 28 March with a Great Plains Saxon direct drill to keep soil movement to a minimum. But 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% germination in this land, and crop competition is im­portant-blackgrass 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."

Optimum timing

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 that traps too much mois­ture in the top couple of centime­tres of soil.

Under this regime yields hit 8.65t/ha last season, while profits neared £1000/ha, 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/m2. 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, was 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. This wheat would yield in the region of 5-7t/ha, which would lose money.

No quick fix

Reverting to winter cropping too quickly can lead to big problems, 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. "This was a massive mistake - we got an enormous chit of blackgrass."

The cover crop/spring wheat sequence was re-introduced this season but was sprayed off due to blackgrass pressure. 'We have lost two seasons of profitable crop­ping and will have to reset the blackgrass control clock," says Mr Woodhead.

"We played our trump card with the plough when we estab­lished Project Lamport. 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.

"We certainly don't want to plough that up again. It can take a number of years to reduce this to manageable levels even without returning blackgrass seed to the soil, which means several seasons of at least 98% control."

 

17 October 2017

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