A change of culture is needed to beat blackgrass, say agronomists

Agronomist Selwyn Rees looking for blackgrass in a field of wheat. Picture: Ian Burt

Agronomist Selwyn Rees looking for blackgrass in a field of wheat. Picture: Ian Burt - Credit: Ian Burt

Agronomists say non-chemical 'cultural control' is becoming an increasingly important tactic in the ongoing battle against blackgrass on East Anglia's arable farms.

Battling the scourge of black-grass is a constant thorn in the side of the region's arable farmers.

And the challenge is not made any easier by a regulatory clampdown on crop protection products, while the rampant weed develops resistance to traditional solutions.

So with chemical options restricted, 'cultural control' has become an increasingly important part of the strategy to keep black-grass at bay, according to an award-winning agronomist.

Selwyn Rees, who was named the agronomist of the year at the Food and Farming Industry Awards in London in December, works from Agrovista's base at Great Ellingham, near Attleborough. He advises a network of 42 farms covering 17,500 acres in South Norfolk between Swaffham, Thetford, Diss and Norwich.

While advising 'stacking' available chemicals to get the best combination of results and to avoid resistance build-up, he is also urging farmers to consider rotational and cultivation changes such as spring cropping, late drilling, careful use of ploughing or cover crops.

'Cultural control has got to be the start of everything,' he said. 'The agro-chemical industry is struggling with the loss of old active ingredients. Through EU laws, the products have to go through re-registration every ten years, and it's getting tighter.

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'So my job as an agronomist is to talk to my customers about how to reduce chemical use, and use more cultural techniques to control black-grass. It is not easy, but we are getting to a point where we are having to really go back to the drawing board as far as rotations go.

'Black-grass is ideally suited for winter wheat production in the UK. It germinates in the autumn, so when the winter wheat crop has been drilled, the weed germinates and seeds before we go to harvest.

'Everything happens within that crop cycle, so we cannot just use a glyphosate on it.

'Some people are switching from winter wheat to spring wheat as it is drilled later and they can use stale seed beds to grow the black-grass and spray it off before they drill the wheat.

'There is also a lot of talk about cover crops. By having a crop in the ground over winter we can capture any excess nitrogen and put more organic matter back into the soil. Some plants will produce roots that will stop black-grass from germinating, but the problem is how do we measure the effect of those things, and how do we cost it for the farmer?'

Minimising the seed return from black-grass plants is an essential factor in controlling the plant's success.

'We need 98pc control of black-grass in order to put fewer seeds back into the soil than we produce,' said Mr Rees. 'It is very difficult to achieve, especially when you are dealing with a resistant population.'

Ploughing, on a rotational basis every three to six years, can reduce the risk from grass weeds by burying seeds below 5cm depth, from which seedlings are unlikely to emerge.

But as the seeds need sunlight to break dormancy – and 60pc of them will die every year if left underground – Mr Rees said ploughing every year could allow them to germinate.

Shallow, non-inversion tillage generally tends to favour black-grass as freshly-shed seeds are retained in the soil surface. But Mr Rees said it does have the benefit of avoiding bringing large numbers of buried weed seeds back to the soil surface.

'If you direct till, or till with minimum surface disturbance, you will lose 60pc a year, so the longer you leave it down there the less it will be viable,' he said.

Mr Rees said agronomists are trying to multiply the effects of chemical and cultural options to find the right solution for individual farms.

'By stacking cultural techniques and stacking chemistry we can get to this magic 98pc control,' he said.

'We are using lots of different types of chemistry and different timings to try and get on top of this problem, but it won't be an instant solution. It is something we are going to have to live with for a long while.'

Are you wrestling with a crop protection problem? Contact chris.hill@archant.co.uk.