As grassweeds continue to rob growers of their yield, the industry continues the search for a solution. CPM delves deeper into some of the key issues as growers get stuck into the autumn drilling window.
New chemistry will be completely useless unless we keep on keeping on with alternative weed control strategies.
By Charlotte Cunningham
Though some progress has been made, grassweed burdens continue to plague arable land right across the country. Integrated weed management strategy is talked about regularly, but there’s arguably still questions over exactly how to combine a multitude of approaches to achieve the best possible control on farm.
When it comes to the grassweed causing the biggest headache, blackgrass still appears to be king, with a recent survey carried out by CPM and BASF revealing that 62% of growers rate this as their biggest weed challenge.
However, there’s other species creeping up the ranks, with 14% calling brome their greatest issue and a further 12% suffering with annual meadowgrass burdens. “What’s interesting about these results it that it gives us a good picture of what is happening nationally,” says BASF’s Steve Dennis. “However, it’s important to note that these pressures could vary massively on a farm-to-farm basis.
John Cussans, weed management specialist at NIAB agrees: “Although blackgrass remains the most significant grassweed in the UK, I think there are an increasing number of other grassweed challenges facing growers in practise and these results show that a significant number of growers cite other weed species as their main challenge.”
With blackgrass stealing the limelight over recent years, John believes it’s perhaps this narrow focus that’s led to the onset of increasing problems with other species. “The issue growers are now facing is that weeds – such as brome, wild oats and ryegrass – are starting to creep through, most likely due to the measures put in to control blackgrass.
“For example, spring cropping can actually encourage other species and many growers are also using less ALS herbicides but without perhaps realising the level of control they were giving.”
There’s also the issue that with more spring cropping being used to control blackgrass, there’s an increasing number of weeds being seen in these crops, adds John. “Meadow brome, for example, has both autumn and spring germination which is causing a few issues.
“In the short term, the solution is vigilance – being aware of your weed burden and putting measures in place to reduce the impact where possible.”
Agrii’s trials manager, Steve Corbett, reckons the increase in other species could be down to a shift in cultivation approaches. “What we’ve seen over the past few years is on land where growers implement more minimum tillage or direct drilling – particularly within barley crops – then more brome seems to be creeping in.
“Likewise, we’re also seeing more pockets of ryegrass where there’s no plough in the system.”
With the events of last autumn forcing many into later drilling or spring cropping, it’s perhaps of little surprise that 38% of growers noted a lower weed pressure during the 2019/2020 season, compared with the previous year. However, it’s important not to be lulled into a false sense of security or take a foot off the gas in terms of weed control, adds Steve Dennis.
Though the autumn no doubt brought challenges for growers, Steve Corbett reckons it actually presented a unique learning opportunity. “One thing we can take from last year is that the chemistry worked very well because it was going into moisture and much later than usual, meaning all of the usual blackgrass flushes had already come and gone.”
And while it still causes headaches for many, John actually believes the UK is getting much better at taking back control against blackgrass. “2012 was probably a bit of a tipping point – it was an awful year, and since then, everyone’s got much better at using the tools they have.
“With declining blackgrass pressure in some areas, agronomists and growers are starting to see the benefits of the improvements they’ve made on farm, and I think the industry sometimes doesn’t get enough credit for the progress we’ve made, but we really have come a long way.”
When it comes to best practice for blackgrass control, the importance of integrated weed management is something that’s been emphasised across the industry for quite some time.
The survey revealed that 78% of growers are including spring cropping in their rotation, 70% are delaying drilling, 56% making use of rotational ploughing, and almost half are hand roguing or deploying crop-destruction techniques in the hope of reclaiming some level of control.
While spring cropping can be hugely beneficial, it’s important to note that not all grassweeds will respond in the same way, warns John. “This is why a combination of techniques is hugely important, so you can be sure you’re covering a broad spectrum of weeds.”
Steve Corbett recommends a traffic light approach when it comes to deciding what controls to implement. “If you assess your fields on a per-field basis, scoring them either as red, amber, or green, it really helps when trying to understand exactly where your blackgrass risk is.
“If red means that the blackgrass is so severe that it’s going to cause serious issues financially and subject you to yield penalties then perhaps it’s time to implement some of the more robust measures, such as rotational ploughing.
“The key point here, however, is ensuring you focus on that attention to detail, and in places where blackgrass burdens are high then decisions must be made on a field-by-field basis.”
When it comes to cultivations, though, many growers are shifting towards a less intensive approach. 56% of growers stated that they use rotational ploughing to control blackgrass – highlighting the importance of the tool that’s become somewhat blacklisted lately, says John. “There are a lot of people using inversion cultivation in a more strategic way – as an intervention rather than as a routine fixed in the rotation. A lot more people are using inversion cultivation in the real world than they let on in the Twitter-sphere which I think is spot on – the plough is still one of the main tools in our armoury to manage grassweeds but in a smarter way.”
With spring cropping topping the list in terms of the most popular control, it’s unsurprising that the survey showed that 71% of growers planted more spring crops than usual in 2020 – though it’s important to remember the conditions that potentially forced this, adds Steve Dennis.
However, whether this decision was planned or not, 55% of growers who planted more spring crops also noted less weed pressure, compared to just 4% who noted a greater presence of weeds.
Despite the reported positive results, the effects of cultural controls – in particular, spring cropping – often take more than one season to come to fruition, says Steve Corbett. “To really draw down blackgrass levels, at least three or four back-to-back spring crops will be needed – this approach is not a one season wonder, it has to be a determined focus and monitored each year.”
Delayed drilling has also been a long-standing ally in the battle against blackgrass. But given the devastating impact of last autumn, there’s likely to be many growers who have been tempted to throw caution to the wind on their weed control and target that earlier window just to ensure crops are in the ground in hope of a more productive harvest in 2021. “There’s certainly been a great deal of fear over whether or not we’ll see the same pattern as last year, however, I can’t stress enough how important it is to hold off if you can,” says Steve Corbett. “I’ve actually threatened to take keys out of tractors just to stop growers going in too early. People are still getting really badly bitten by blackgrass and we don’t want to encourage that this year, particularly following a difficult season.”
At the time the survey was conducted (Jul 2020), 29% of growers said they planned to drill the majority of their crop in early Oct, while 23% said they’d be hanging on until the middle of Oct, and just 4% revealed they’d be drilling as early as they can.
When asked about their approach in general this year 41% said they’d be waiting to judge the weather.
So what’s the best way to strike the balance between optimal weed control and a profitable crop?
“Firstly, it has to be said that it’s incredibly encouraging to see that not many growers are aiming for that earlier slot, despite last year’s autumn, which just shows how much awareness there is regarding the role that drilling plays in potentially reducing weed burdens,” says Steve Dennis.
“While it’s tempting to wait to judge the weather, quite often it’s impossible to drill all of your cropping area in the short weather windows, so my advice would be to go when you can, prioritising the less affected fields first.”
John agrees: “It’s inevitable that some growers will have been swayed to drill earlier this year, because the hard truth is that we simply cannot afford to have another year where we don’t have crops in the ground.
“The limited data we have on sowing date trends show that the trend towards earlier drilling is slowly being reversed, however you can also see year-to-year variability and this is actually correlated with the weather during the season before and not the current season, which is slightly unnerving.”
“However, most growers will also be aware of an ‘optimum date’ from a weed pressure perspective, so if you’re thinking about drilling earlier going forward, the advice from me is to drill the fields with less pressure first to avoid creating further issues down the line.
Though the weather poses perhaps one of the greatest challenges to growers, it’s unfortunately an uncontrollable factor.
Other than the weather, the survey highlighted that resistant weeds present the next biggest challenge for 33% of growers, while 31% said they struggle due to a lack of chemistry, and a further 28% noted limited rotation choices as their biggest issue.
“Limited rotation choices really means a limited number that are profitable I think, and in an ideal world if you could offer me one thing going forward it would be more crops that make money,” says John.
“Lack of chemistry seems a bit unfair as we have lots of herbicides to choose from compared with some countries – though a wider base in terms of mode of action would be a massive benefit, of course.
“However, it must be said that simply adding a couple of new modes of action isn’t going to solve the underlying issues with weed control. We can’t get back onto the treadmill of not doing the right thing culturally and just waiting for a new herbicide to come along.”
Steve Corbett echoes these sentiments. “There’s no doubt that resistance has meant people have hit a brick wall very rapidly – the dramatic drop off in terms of performance has been really quite staggering. However, this has come as a result of our own behaviour – overusing chemistry and implementing continuous cereal rotations – so we’re entirely responsible about the protection of any future chemistry and ensuring we don’t break it and cause more resistance issues.
“We know there’s products in the pipeline, but they’re going to be useless unless we keep on keeping on with these alternative weed control strategies.”
Working in harmony
With a new mode of action on the horizon from BASF, it’s crucial to not forget the value of cultural controls and the role they’ll continue to play alongside whichever chemistry may or may not come to market, says Steve Dennis.
According to the survey, if BASF were to conduct farmer trials for new herbicide chemistry, but also incorporated cultural controls, 44% of growers said they’d be interested in learning more about how cultivation techniques could work alongside the product, 29% noted they’d like to know more about weed control without glyphosate, and 11% said they’d like to see the effect of rotations on any new chemistry.
“What BASF has realised is that if we launch a new herbicide, it needs to have the full package – meaning it’s essential that we work to understand how it fits in with other agronomic approaches,” says Steve Dennis.
“What we generally find, however, is that by incorporating a wide range of alternative controls we actually achieve better performance from the herbicide, meaning it fits in harmony with cultural approaches, rather than replacing them. This has been true for Crystal which still gives the best start for blackgrass control and it will be true for new herbicides when they become available.”
Winner announcement
Congratulations to our winner Fergus Hawkins from Devon who responded to the CPM/BASF survey on grassweed control and has won the fabulous prize of an iPad 11 Pro worth £869.
Fergus responded to the survey and completed the tie-breaker question asking participants to give their views on the most neglected tool when it comes to battling challenging weeds and why.
His comprehensive answer impressed the judges by stating that field drainage is something we can improve on easily and is neglected on most farms. “Better drainage allows later drilling, ease of travelling with pre and post em herbicides. You can get on to the ground earlier in the spring with weeds growing rather than being saturated in water. If weeds are actively growing, they have more chance to uptake the lethal dose of herbicide. Crops grow away from the weed burden, suppressing seed numbers through competition.”
The aim of the survey was to explore the ongoing issues surrounding grassweed control.
To take part in the next survey, make sure we have the correct details for you by emailing angus@cpm-magazine.co.uk
