As featured in Arable Farming Magazine
Black-grass control – as good as it gets?
by Arable Farming Magazine September 2022 issue
For more than a decade, black-grass has been the foremost agronomic problem on many arable farms. But have most farmers now found a way to manage it?
A team of scientists at Rothamsted Research has monitored more than 160 arable fields for eight years to measure black-grass levels and record agronomic practice.
Since the project began in 2014, there has been a gradual decline in black-grass levels.
Weed ecologist Laura Crook says: “Black-grass levels have definitely come down since the project began.
We see far fewer fields with very high infestations and much more at the other end of the scale.
“Over the same period, we have recorded more delayed drilling, stacking of residual herbicides and spring cropping.
These are the main factors behind the change, with spring cropping making the biggest single difference.”
Her colleague Richard Hull points out that farmers’ overall approach to weed management has gone up a gear.
He says: “There are three stages to weed management: planning it, doing it and monitoring the results. I think this third step is where the big improvement has come. Farmers have been able to understand why something has worked and take that into next season.”
There is a lot of variability across 160 fields.
Some of that is down to seasonal differences, particularly whether conditions favour high levels of control from residual herbicides.
But a lot of it is due to farmers’ weed control strategies.
“Some fields continue to have high levels of black-grass because, for one reason or another, the agronomy and rotation has not really change
“Other farms have made sweeping changes to drastically reduce weed numbers.
A third group sits between the two and has more mixed results, depending on the season.
“Each farmer has a level of black-grass they are willing to live with.
For some it is zero tolerance but for others it is higher, but not significantly sapping yield.
I think there has been a plateauing of control with the tools available for many farmers,” says Mr Hull.
Looking ahead to this autumn, he expects dry conditions will work in farmers’ favour to allow good control of black-grass ahead of cereals.
“My guess is dormancy should be low. The four-week maturation period in June and July was fairly hot and dry. As soon as there is enough moisture, black-grass will germinate quickly and be controlled ahead of drilling.”
Advising farmers in Somerset, Dorset and Wiltshire, Agrovista agronomist Peter Waltham advocates a field-by-field approach.
“Farmers are now very good at using cultural controls such as spring crops, minimal disturbance and delayed drilling.
I think they are also more pragmatic; they know it takes more than one season to sort it out.
Plus, farmers can still get a good yielding crop with low levels of black-grass, I don’t think that’s a problem as long as they have a long-term plan to keep it under control,” he says.
He identifies a greater willingness to manage fields and crops in more detail to solve a problem in a specific field rather than a farm-wide approach.
This is particularly important when deciding how to manage land in those critical weeks between harvest and drilling.
“It’s all about a tailored approach.
The most important thing is to ask what you are trying to achieve and how are you going to do it.
“This will be different depending on the field, following crop and so on.
I am expecting a higher number of second wheats this season, which isn’t a problem for weed control, but these fields are best drilled later.
“In wheat crops, black-grass control is based on robust cultural controls and autumn chemistry.
Last season, the standard pre-em was Liberator + Proclus.
“I first saw it at Agrovista’s Lamport site. You could see an improvement in control compared to other products, so I was keen to use it. So far it is working well and farmers have generally been happy about the results.”
However, Bayer’s Tom Chillcott offers a note of caution to anyone thinking the black grass challenge is solved.
“Bayer has seen first-hand how the market for herbicides and the discussions people have about black-grass have changed.
Cultural controls are now the first line of defence and herbicides are what you use to finish the job.
“But in winter wheat and to a lesser extent winter barley, effective herbicides have been essential in reducing black-grass numbers while producing profitable crops.
We need to maintain efficacy and do our level best to prevent resistance.
Modes of action
“At the pre-em timing there are now multiple modes of action available so it’s possible to vary modes of action in season and across the rotation to prevent resistance.”
In the field
Essex farmer David Lord agrees black-grass control has stabilised, but he is on guard against complacency.
“The changes we made quite a few years ago have reduced the peaks; we don’t get the build up of really high populations mainly because of spring cropping.
We still have persistent populations across the farm, but it is manageable,” he says.
He thinks finding spring crops which suit the system is essential for durable black grass control.
Spring oats have been the most important, however, Mr Lord thinks there is a slight uptick in the amount of black-grass he sees.
“We drill in early- to mid-April, but some black-grass comes up even after this.
I wonder if we are selecting for spring germination because blackgrass finds a way?”
If spring germination becomes more of a problem, he will consider stewardship options to take the worst land out of the rotation.
He recently cut a crop of canary seed.
It is drilled late and is quite competitive, so it seems to be a good additional spring crop option, he says.
Adopting a regenerative approach is an important part of staying in control.
“We use cover crops and reduced tillage to improve soils, they are healthy and resilient and able to cope well with a bit of adversity,” adds Mr Lord.
Winter wheat is typically grown one year in three in the rotation.
Delayed drilling and pre-emergence herbicides are vital here, but the system overall does not put too much pressure on chemistry.
“We are not using huge stacks, but they bring a huge amount of control, we can see that with the occasional spray miss.”
But Mr Lord’s experience suggests black-grass will not ever be straightforward to control.
The reasons it became such a problem have not changed: it is still competitive in winter wheat, produces lots of seed and is quite often resistant to post-emergence chemistry.
Against that are the facts that earlier drilling and second wheats are both tempting options for farmers looking to maximise profitability but choosing low-risk, low weed population fields is essential.
Research and anecdotal evidence suggest farmers have found ways to manage black-grass, but the changes to rotation and agronomy required are here to stay.