Arable News

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Black-grass control Looking at the long-term legacy

As a location to study the effects of black-grass control over time, crop protection and seeds business Syngenta may have hit the jackpot with its Barton site near Cambridge.

As part of Larkrise Farm, two years ago this heavy land site was yielding as many as 650 black-grass heads/m2. At 100 seeds per head, that equates to 65,000 seeds/m2 being returned to the soil each season.

An unsustainable situation for any farm, particularly with 2016 tests confirming three types of herbicide resistance present, but as good a place as any, perhaps, to begin an in-depth and innovative study of the long-term effects of a matrix of cultivations, crop rotations and pre-emergence herbicide applications on black-grass control.

And in-depth it certainly is. As well as a focus on the effects of plough-, min-till- and direct drill-based establishment systems across winter and spring cereal regimes, and all aspects of cultural and chemical control of black-grass in-between, Syngenta has also brought its long-held spray application knowledge to the trials site.

The benefit of quicker establishment with the use of a seed treatment when drilling late, as well as crop residue management, is also a focus.

Furthermore, to add a little extra interest, even propane burners and black-grass seed ‘vacuuming’ have been employed in plots to see if the removal of the season’s seed return can really make a difference.

As Syngenta field technical manager James Southgate explains, Barton is more than just a series of trial plots. “In what is likely to be a five-year matrix, we are trying everything here in order to be able to help growers progress with their black-grass control, rather than it standing still or, worse, going backwards,” he stressed.

“Black-grass is an on-going problem on many farms and if just one of the pieces of the jigsaw is missing, then it’s very hard for a grower to move forward in terms of overall control,” Mr Southgate pointed out.

“Not all farmers are specifically interested in the decisions surrounding the chemistry that’s applied to their crops, but using this site as a hub for farmers we can also demonstrate that what they cultivate with, what they grow, or how they use their sprayer, for example, can make a big difference to the success or otherwise of their black-grass control,” he said.

Different cultivations

In autumn 2016, the main body of the trials site was divided into a grid featuring 12 and 24m width strips. The narrower plots all featured winter wheat variety Shabras, and each was allocated a different cultivation method including ploughing, min-till (to a depth of 12–13cm) and direct drilling (ie no cultivation prior to the drilling). 

The larger plots were all direct drilled, containing hybrid winter barley, spring barley and spring wheat.

Pre- and post-emergence herbicide stacks, as well as untreated, were applied across all crop types and methods of establishment, and plots taken to yield.

In autumn 2017, the plots were rotated 90 degrees to overlay 2016’s matrix of rotation and cultivation trials.

Although Mr Southgate concedes that this is only the start of a long-term study of the effects of black-grass control over time, he believes that some of the initial findings are already giving visitors to the site some food for thought.

Ploughing in autumn 2016 ahead of drilling winter wheat, which was then followed by a pre-em herbicide application, gave the best control of black-grass that year, said Mr Southgate – considerably better than when a pre-em was omitted, he noted.

“There was also a 6 per cent difference in control between a pre-em only, compared with a pre-em followed by an early post-em residual application,” he continued. “You can question whether this 6 per cent difference is worth it – but it’s well documented that 97 per cent black-grass control means that you are standing still, however that extra 6 per cent got us to 98 per cent control.

“That’s the difference between continuing to go backwards, or getting to the point of going forwards and making progress with control.

“Always try to maximise black-grass control,” advised Mr Southgate. “Don’t cut back otherwise it comes back! Stack as many different actives as you can at pre-em,” he said.

Syngenta’s pre-em trials included a number of actives including Crystal (flufenacet + pendimethalin) at 4-litres/ha + 60g/ha DFF + 3-litres/ha Defy (prosulfocarb). 

“This kind of stack provides more control – but on farm, if your seedbed isn’t perfect, then crop safety can be an issue with this many actives, so perhaps it’s best not to put all your eggs in one basket at pre-em but go with as many as are reasonably possible.

“A flufenacet base plus 3-litres/ha Defy should be considered as a minimum for pre-em,” he added.

In terms of post-emergence options in 2016 trials, a 0.3-litre/ha rate of Liberator (DFF + flufenacet) + 2-litres/ha prosulfocarb was applied 18 days after the pre-em. “Our advice is to do it within three weeks of the pre-em so that any black-grass that survives the initial treatment will be at the 1-leaf stage for the second application. It’s better to control them early, as these will be the plants that have the bigger heads and produce the greater return of seed to the soil if allowed to survive,” explained Mr Southgate.

“Preventing seed return is the most important thing where progress with controlling black-grass is concerned,” he stressed.

Despite the direct drilled winter wheat plot suffering the worst level of black-grass control, interestingly it delivered the highest yield (harvest 2017) compared with the ploughed and min-tilled plots. This, according to Mr Southgate, was due to a lack of moisture in the plots where soil had been moved by the cultivation and subsequently dried out – the ploughed strip delivering the lowest yield.

Seed treatment boost

In autumn 2017, plots comparing late September-drilled winter wheat with early November drilled, demonstrated that the delayed drilling date significantly reduced black-grass pressure, continued Mr Southgate, who said that when drilling later the aim is to establish wheat as quickly as possible, to achieve quick growth and smother any black-grass.

In trials at Barton with the company’s latest seed treatment, Vibrance Duo (fludioxonil + sedaxane), he said that while the difference in speed of crop emergence was minimal between treated and untreated seed, one additional tiller per plant was seen where the treatment was used.

“Where you really see the advantage of Vibrance Duo is when wheat is struggling and under pressure from black-grass on heavy land. I’m not sure if getting that extra tiller suppresses black-grass additionally, or not, but if crop production is about margin, then it’s likely to give you more yield.

“We’re seeing that affect through all types of cultivation,” he added.

Grains of truth

In a study to see how different cultivation directly affects grass weed seed in the soil profile, 65,000 rice grains/m2 were applied to the soil surface in plots in 2017 – replicating the number of black-grass seeds/m2 returned in the previous season at Barton. Cultivations included shallow (max 5cm depth), min-till (12–13cm depth) and ploughing (20cm depth).

“Establishment systems are so different and it’s important to get growers to think about where returned black-grass seeds will end up in the soil profile as a result of their cultivations,” said Mr Southgate.

The plough’s skimmers took the soil surface and rice into the bottom of the furrow, 20cm below ground, which would have kept it out of the germination zone, and proved less of a burden to the following crop, while shallow cultivation kept the grains close to the surface and within the germination zone.

“However, the trial demonstrated that when using min-till, some seed remains on the surface but it is also mixed all the way through the soil profile right down to the cultivation depth.

“This was confirmed on the site in 2017 where, although crop establishment was better with min-till than the plough, there was more black-grass in evidence,” he said.

“People have used min-till for many years and it looks good in terms of crop establishment, but you never know where the black-grass seed is in the top 12cm of the soil profile. And if the same regime is maintained for a number of seasons, it’s difficult to know what to do to control the black-grass, unless you plough early and start again with a stale seedbed.”

Mr Southgate said that direct drilling across the plots in 2017 resulted in a thinner plant stand which is likely to result in lower yields this harvest.

The combination of drilling winter wheat seed late and into tight soils covered in crop residue last autumn, meant that even in the best-established plots (min-till), establishment was only 50 per cent. However, where a 5cm pass with a Carrier cultivator was made ahead of direct drilling, establishment was much better.

“Black-grass dormancy has also been high during the past two years and there was a lot of spring-emerged black-grass in 2018,” said Mr Southgate.

“The lesson is that if you allow light into the crop, black-grass keeps coming through and – worryingly – often outside of the control programme.

“Growers must maximise establishment,” he added. 

Spring crops

Common across the spring barley and spring wheat crop plots over the past two years has been the high level of black-grass populations, said Mr Southgate.

“Last year when comparing spring barley versus spring wheat there was no difference in the black-grass populations that came through with the crops. But it is important to know that spring barley reduced the number of black-grass heads by 32 per cent, compared with spring wheat.

“This year it has been the same. Spring wheat certainly has its place but if you can grow the most competitive crop, ie spring barley, then do so as there is considerable difference in the number of black-grass heads/m2,” he advised.

According to Mr Southgate, spring barley direct drilled into an over-wintered oat stubble in late April last year a was a mess in terms of black-grass, despite 20 black-grass plants/m2 being sprayed off ahead of drilling in the spring.

In another plot, a shallow (5cm) pass with a Carrier was made in the stubble in early October before being sprayed off prior to the spring barley being drilled. “Here, 80 black-grass plants/m2 were sprayed off – a difference of 60 plants/m2 compared with the uncultivated stubble.

“As well as better black-grass control using the Carrier, the crop achieved better establishment too. A little soil movement early on allows the black-grass to come through and then be sprayed off prior to drilling.

“Dormancy is a factor here and we know that about 20 per cent of black-grass establishes in the spring. In the crop that had no cultivation prior to drilling, the black-grass came up later in the crop, whereas the extra cultivation in the autumn helped with black-grass control and crop establishment.”

Mr Southgate also posed the question as to whether there would be a benefit from a shallow cultivation in the spring, rather than the autumn, ahead of drilling a spring crop.

“We found initial crop establishment was better with good-seed-to-soil contact, but moving the soil germinated more broad-leaved weeds. They were wide rows but better establishment also meant improved competition from the crop. 

“This method can be risky though as the later cultivation can mean the soil dries out but If you are confident that the conditions are suitable, and the crop will benefit from the cultivation for establishment and competition for the black-grass, then do it,” commented Mr Southgate.

Wide rows

With the question of using wider spaced crop rows to help with trash flow when drilling, other plots in the spring trials highlighted the problems associated with black-grass competing for light between rows, causing crops to grow upwards rather than outwards due to the competition.

Where spring barley row widths were tightened from 16.70 to 8.35cm, and crop seed rates remained the same (450 seeds/m2), typical black-grass plant heads were smaller and tiller numbers were reduced, resulting in less seed return.

Residue result

To gauge the affect that straw residue has on the efficacy of pre- and post-em herbicides when targeting black-grass, Syngenta applied extra straw to seedbeds ahead of spray applications.

“We broke a bale and put extra residue on the surface meaning it was difficult to hit the soil with the herbicides,” he explained.

“In untreated plots, ie where there was straw without chemistry, black-grass germination was less than plots with no straw and no chemistry – possibly because of the lack of light.

“But in herbicide treated plots – much less black-grass control was seen where there was excess straw due to herbicides binding with the residue and not the soil.

“Residue management is very important in terms of maximising the efficacy of the residual chemistry, and if you are not going to bale straw then it is likely that there will be an effect.

“Those drilling straight into trash must spread it as evenly as possible beforehand otherwise it could reduce herbicide efficacy. And, obviously, following on from a crop like spring barley is going to be easier than following a second wheat in terms of the amount of biomass to deal with.”


Syngenta has long been associated with nozzle application work and it continues to be a focus at Barton.

“Historically we’ve talked about 100-litres/ha with a Defy 3D nozzle but over the past two years we have seen a marginal improvement in black-grass control at 200-litres/ha compared with 100-litres/ha applications,” commented Mr Southgate. “Last year however we compared a whole range of water volumes and 200-litres/ha always gave the best control no matter which nozzle was used, although control in plots where Defy 3D and 90 per cent drift reduction nozzles were used was best. 

“Overall the best pre-em spray control was achieved using a 90 per cent low drift nozzle but there is definitely resistance from growers to using that rate,” he said.

“If we can reduce drift then we should be doing it by using drift reduction nozzles,” suggested Mr Southgate. “We are not saying that this means you can spray in conditions when you shouldn’t be, but we know spraying is taking place on marginal days and that’s when drift reduction is key.

“They are good for the environment and good for the crop.”

In boom height trials, while drift reduction and flat fan nozzles achieved the same level of control at 0.5m above the ground, at a raised height of 1m, when more drift is likely, control using drift reduction nozzles was improved compared with flat fan.

“It’s about using everything you can to do the job properly,” concluded Mr Southgate. “Otherwise the black-grass situation will only get worse.”


Top pre-em tips from FSOOTY finalist

Finalist in this year’s Farm Sprayer Operator of the Year Awards, Northamptonshire-based arable foreman Steve May is responsible for covering around 4,500ha of arable cropping and grassland each year for the home farm (Fromant & Sanders, Kislingbury) and six contract clients.

He reckons his typical daily coverage when applying pre-emergence herbicides is between 70–100ha with his 24m trailed John Deere 740 sprayer. In ideal conditions he uses 05 3D nozzles at 200-litres/ha water volume (previously 150-litres/ha), travelling at 12kph and with a boom height of 50cm .

Where spraying conditions are compromised, speeds are marginally reduced and he switches to 90 per cent drift reduction nozzles.

Mr May admits that factors such as higher water volumes, distances between fields and folding/unfolding booms eat into daily pre-em spraying outputs, and so he provides the following top tips to help sprayer operators mitigate any loss in operational time:

  • Start early to make maximum use of daylight hours and fit boom lighting to prolong the working day
  • Run a water bowser or have satellite water tanks positioned around the farm
  • Watch the weather forecast closely
  • Don’t drill more ground than you can spray in the weather window available
  • Make sure chemical is on the farm before it’s required and inform your agronomist when the crop is being drilled

Lessons being learned for host farmer

Tim Scott has been a tenant on the land that makes up the trials site at Larkrise Farm, Barton since 1998, the year it came into the ownership of the Countryside Restoration Trust (CRT)*.

A farmer with a keen eye for environmental stewardship and conservation, Mr Scott has been involved with CRT for many years, as well as having had a long-term relationship with Syngenta particularly where nozzle application work is concerned.

He explained that four years ago the site, which he describes as featuring “exceptionally” heavy soil, was relatively free of black-grass and there was little cause for concern.

However, in the spring of 2015 he drilled canary seed and after harvest it turned very wet.

“There were signs of some black-grass in the canary seed when it was growing although nothing unusual for a heavy land farm,” pointed out Mr Scott. “But because of the rain following harvest I couldn’t get on with my usual min-till approach to autumn establishment. So I was forced to plough when I didn’t want to, to try and get a seedbed. It consequently made a terrible job of it and, in places, I had to plough twice and I still struggled to get a decent seedbed,” he explained.

According to Mr Scott it was the perfect storm. His ploughing had brought several seasons’ worth of black-grass seed to the surface, highlighting the significance of seed dormancy, and because of the poor seedbeds the pre-em herbicides were also less effective than usual.

“It was a lesson,” he concedes. “In hindsight, and with a mess like that, I should have sprayed it all off and waited until the spring. Perhaps as farmers we are sometimes a little short-sighted in that we don’t think back far enough as to what we’ve done and how that might affect the next crop in terms of pressure from black-grass.”

In following developments with Syngenta’s trials, of key interest to him has been the moisture retention advantages gained from direct drilling, he said.

Direct drilling has delivered much greener, healthier looking crops each summer compared with ploughing and min-till establishment methods, in addition to an increase in yield.

“The three or four more days extra grain fill achieved by direct drilled crops makes all the difference to end yield and I’m not sure if farmers are looking at this aspect of their crop establishment enough,” he suggested.

Another message from the trials work he is keen to share is that of water rates and pre-emergence herbicides. He said that in autumn 2016 he began his pre-em spray applications at rates of 100-litres/ha. However, after discussions with Syngenta, he changed rates to 200-litres/ha and switched to 90 per cent low drift nozzles to complete the pre-em programme. 

“When applying fertiliser in the spring I noticed two or three fields where weed control hadn’t worked well and these were where I had applied pre-ems at 100-litre/ha.

“The same result was also seen very clearly in the trials,” he added.

“A few years ago there wouldn’t have been such a difference in performance between 100- or 200-litres/ha rates but with resistant weeds creeping in, we are now seeing the differences in control being highlighted,” concluded Mr Scott. 

*Celebrating its 25th anniversary in 2018, the Countryside Restoration Trust (CRT) was established in 1993 in response to growing fears about intensive and industrialised farming. The CRT promotes a working countryside using sensitive and sympathetic farming practices that encourage and protect wildlife to produce quality food.

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