Why the control of black-grass needs a rethink – Farmers Guardian

Ever adaptive, black-grass is changing – and that means approaches to its control must change too. That was the message from Hutchinsons technical manager Dick Neale to growers attending the firm’s Cambourne Grass- weed Demonstration open day at the Clear family’s South Sea Farm near Cambridge.

Mr Neale said that good progress had been made with reducing populations of September-emerging and October-emerging black-grass on the farm, but full control of the grass- weed was still not being achieved.

Trials at the 40-hectare site will build on findings from Hutchinsons’ long-running former grass- weed site at nearby Brampton.

“What we are seeing here, and what we are seeing across a range of our off-site black-grass trials, are black-grass numbers that are a factor of 10 lower than the ones we were dealing with in the days of Brampton,” said Mr Neale.

“Populations at Brampton were 400, 500, 600 black-grass plants per sq.m. Now we are dealing with 40, 50, 60 plants/sq.m, but their ability to tiller is strong.”

Key areas of work include the im- pact of cultivation practices, drilling date, soil health, cropping systems and drainage on black-grass populations and their management. How Sustainable Farming Incentive management practices can affect black-grass is also being examined.

Mr Neale challenged growers at- tending the event to reflect on the black-grass control they are achieving in their stale seedbeds.

“Are you seeing the same performance from your September stale seedbeds that you saw five years ago?” he said.

“I am certainly not, and that is because for the last eight to 10 years, we have done an extremely good job and have largely exhaust- ed that huge late September, early October population of black-grass.”

Black-grass is emerging later, and its emergence is more protract- ed, but there is less of it. Data suggests that moving the drilling date for winter wheat earlier – to early October – could increase crop competition against black-grass during autumn, said Mr Neale.

“Because we are dealing with less black-grass, there is a strong argument that we should drill a bit earlier and create a competitive crop against that lower population of black-grass.

“I am not talking about the middle of September, and I do not yet fully have the answers, but it is something we will be looking at going forward,” he added. Another aspect of crop competition under investigation is the use of variety blends.

“One of the reasons we are growing a blend of wheat here is that I want more diversity of rooting in the crop to compete with the rooting of the black-grass,” he said.

This follows AHDB-supported PhD work showing that black-grass is outcompeting wheat because of the weed’s greater root mass.

“Can we select varieties or blends of varieties that compete with black- grass from a rooting point of view?” said Mr Neale.

Accurate pinpointing of where black-grass is on the farm is being achieved using Hutchinsons’ Omnia digital farming platform to map weed populations.

Elsewhere on the site, black-grass emergence following different glyphosate application timings is being tracked. Plots were sprayed off with glyphosate at two-week intervals between early October and late November last autumn (see table, below) and black-grass emergence recorded.

“Every time we made an application of glyphosate, we got a further germination of black-grass plants right until the end of November and we were getting quite significant numbers in terms of their impact in the crop,” said Mr Neale.

While the 16 plants recorded following a November 26 glyphosate application might not seem like a big number, careful management is needed.

“I suspect that what I am seeing is exactly what is happening on your farms, whether you realise it or not. These are where your numbers are now, and you need to be very specific in your management of them,” Mr Neale told visitors.

Each of the 34 black-grass plants recorded in the untreated plot at the end of November had only to tiller out to cover an area equivalent to an A5 envelope to result in complete field cover, he added.

“It is not a lot of plants but it is about the ability of those plants to tiller, and we are seeing that as being extremely strong at the moment – a few plants producing a lot of tillers, giving a lot of ground cover, suggesting you have got a lot of black-grass, but you have not-you have got a smaller number of very aggressive plants.”

In another approach, data generated by the TerraMap high-resolution soil scanning service is being used to map the heavier, more moisture-retentive soils on the farm, enabling inputs to be targeted in areas where black-grass is most likely to be found.

TerraMap is also being used to monitor plant available water, again linked to heavier soils.

“More water in those areas pro-motes more black-grass, or at least allows more black-grass to survive,” said Mr Neale.

With a wide range of seed drills available for use in reduced tillage farming systems there is a need to consider the effect of drill row width on black-grass, Mr Neale told the meeting.

“You may be using Horizon, Horsch, Claydon, Mzuri drills – they are all very different, yet we put the same seed rate through them,” he said.

“It is becoming obvious that that is not what we should be doing. When we are using a wide row setting, we need to put in fewer seeds per hectare to establish the right spacing down the row, so that those plants have got room to spread out and tiller.”

Using the latest technology to help better understand soils is a key theme at South Sea Farm.

Soil organic carbon to clay ratio, available sulphur, and calcium to magnesium ratio are just some of the measurements available through the TerraMap soil scanning service that can help inform black-grass management, visitors to the Cambourne Grass-weed Demonstration open day heard.

Highlighting data showing an available sulphur deficiency identified in a field at South Sea Farm, services specialist Jade Prince explained how this had adversely affected germination and establishment in the winter wheat.

“If a crop is not establishing as we would like, and it is not well as getting away and competing with black-grass, that straightaway gives an easy gateway for black-grass to start proliferating,” she said.

“We need to make sure that all the nutrients that our crops want are available, giving them the opportunity to grow away and outcompete black-grass.”

The cropping system includes winter wheat and spring barley implemented in a 3C rotational system that incorporates catch, cover and companion crops.

Key features of the cropping system include:

• Winter covers and companion crops claimed under Sustainable Farming Incentive 2023
• 127 hectares of zero tillage
• Winter and summer covers are a six-plus species mix
• Companion crop used is beans at 30kg/ha
• Flexibility allows for inclusion of oilseed rape if establishment conditions are favourable