Blackgrass control strategies should change and adapt if growers are to keep on top of this constantly evolving threat, say experts. CPM visits Hutchinsons’ Cambourne grassweed demonstration to learn more.

“It’s about questioning and scrutinising everything that may, or may not, have an impact on blackgrass.” DICK NEALE

By Rob Jones

When it comes to weed control, important changes observed at South Sea Farm – home to Hutchinsons’ blackgrass demonstration site – are protracted germination, and populations dominated by fewer but more aggressively tillering plants.

According to technical manager, Dick Neale, this is representative of many other farms across the country, therefore it could be time for growers to refine their grassweed management approaches accordingly.

In the case of South Sea Farm in Cambourne, a range of approaches are now being taken. “It’s about questioning and scrutinising everything that may, or may not, have an impact on blackgrass,” says Dick.

“In many cases, we’re optimising simple factors, from cultivations, cropping, variety choice, and seed rates, to drill type, sowing date, and placed nutrition to increase crop competition. There’s no single answer.”

Mapping blackgrass populations and identifying potential causes is key to targeting control strategies and technology can help, suggests Dick. At South Sea Farm, field populations have been mapped in Omnia and then overlaid against Terramap soil analysis.

Soils specialist, Jade Prince, explains that properties such as the silt:clay ratio, plant available water, organic matter content, and organic carbon:clay ratio are all useful indicators to highlight where the heaviest, wettest, soils are, and therefore where blackgrass is likely to thrive.

Other factors such as the calcium:magnesium ratio also provide a good indication of soil ‘tightness’ and workability. “Here we have high magnesium content soils, so we’ve used gypsum to address the issue – gypsum allows magnesium to flush lower into the soil so the seedbed becomes more friable.”

Poor drainage has been identified as the main cause of many blackgrass issues at Cambourne, meaning a concerted effort to repair existing drains and mole plough problem areas, points out head of farm business consultancy, Will Foyle.

“Poor drainage not only increases waterlogging and creates conditions for blackgrass to thrive, but it also reduces crop establishment and growth, and compromises the ability to travel on land at the optimum time for cultivations, drilling, or herbicide applications.”

A cost benefit analysis of growing spring barley with and without good drainage has indicated the case for rectifying problems (see table). This analysis is based on yields from a crop of Planet spring barley grown at the site in 2024, where drainage problems were evident on parts of the field during the exceptionally wet spring.

 Without drainageWith drainage
Yield (t/ha)3.757.25
Output (£/ha)7691486
Variable costs (£/ha)478500
Fixed costs (£/ha)475475
Net margin-184511
Drainage cost (£/ha) – assumes an average cost of £3000/ha, borrowed at 4.5% over 10 years0373
Blackgrass seed return (%)15035
Adjusted net margin (£/ha)*-244178
* Adjusted net margin assumes additional inversion cultivation cost of £60/ha to address extra seed return without drainage, and a herbicide saving of £40/ha where drainage has been improved and seed return is lower.

“Such conditions won’t occur every year but are becoming more frequent. Yields were broadly representative of spring barley grown elsewhere on the farm that year, with poorer areas averaging just under 4t/ha and better land just over 7t/ha,” notes Will.

“Drainage is something we can’t neglect as it offers one of the greatest returns on investment. In this scenario, we were effectively £422/ha better off by investing in drainage – getting better crops, reducing blackgrass and returning more money to the business.”

As for protracted germination, one trial at Cambourne has illustrated the patterns now being seen, where plots were sprayed off with glyphosate every two weeks during the autumn and subsequent blackgrass emergence recorded.

“After every glyphosate application there was further germination right through to the end of November,” says Dick. “They weren’t big numbers – 16 plants/m2 at the 26 Nov assessment – but they did keep coming.”

Like many farms, stale seedbeds have been used successfully for the past 8-10 years, largely exhausting the late-September/early October blackgrass population, he adds.

“Therefore we aren’t seeing the same performance from stale seedbeds anymore. Blackgrass numbers are down by a factor of 10 compared with what we used to see at our old Brampton site. Instead of 400-600 plants/m2, we’re now dealing with 40-60/m2. However, their ability to tiller is strong with some producing more than 40 tillers per plant.”

Dick adds that because of the lower blackgrass pressure, there’s an argument for drilling slightly earlier to help to create a more competitive crop. “It’s something we’re looking at in the trials, as well as other ways to maximise crop competition.”

In terms of herbicide programmes, the shift to more protracted germination has had significant consequences. According to ADAS’s John Cussans, this means well-timed sequences offer more effective control compared with large stacks of residual chemistry.

Not only has this been was evident during a herbicide trial at the site, but mirrors results elsewhere, suggests John. “We’ve seen across a lot of different trials, that a herbicide sequence is more robust and gives the highest level of blackgrass control compared with putting everything in the tank pre-emergence.

“Even with our best products, we still find they’re better used in a sequence rather than as a single product at a single timing. But, we must maintain tight sequences, which for a September/October drilled wheat, might start with a pre-em straight after drilling, followed by a second application 5-10 days later.

“As soon as that second application is delayed too long, control can really drop, so you have to be able to make it work,” he stresses.

*****************************************************************************************************

This article was taken from the latest issue of CPM. Read the article in full here.

For more articles like this, subscribe here.

Sign up for Crop Production Magazine’s FREE e-newsletter here.