Arable News

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Cultivating ideas to boost weed control and crop establishment

Syngenta has been looking at the interaction between direct drilled, min-tilled and ploughed plots of winter wheat and winter and spring barley at its black-grass trials site in Barton, Cambridgeshire. The company has begun looking at how herbicide programmes could be adapted based on cultivation, soil type and drilling date, which could influence the amount of grass weed emerging. 

When comparing the performance of the three different cultivation methods at the trials site over the past two years, headline figures suggest that, in 2017 and 2018, direct drilled wheat plots achieved the best margin (over establishment and herbicide costs) despite in 2018 achieving the lowest yields. However, this has to be balanced with the fact that, in 2017, direct drilling returned 10,000 more black-grass seeds/m2 compared to the plough.

Looking at black-grass control comparisons; in 2017 the direct drilled plots returned the worst control (91 percent), compared with the best – the plough – at 98 percent control and min-till at 92 percent (and all following pre-emergence and spring post-emergence herbicide treatments).

In 2018, following a pre-emergence of Defy + Crystal + DFF (and where untreated plots featured 460 black-grass plants/m2), the plough and direct drill achieved the best control of 97.9 and 97.8 percent respectively, and min-till 95.5 percent control.

Interestingly, where min-till in 2017 was followed by min-till in 2018, this gave the poorest control of black-grass at 92 percent.

2019 observations

With the potential loss of glyphosate looming, Syngenta is looking at how best to use residual products when drilling early. Allowing the black-grass to emerge after drilling, then spraying a residual. Comparing this to drilling later in the season when the weather can delay spraying, leaving the growers to rely on a ‘one hit opportunity’.  

“In an early drilling scenario we would expect to see a benefit from sequences of herbicide treatments that will prolong control over successive flushes of grass weeds,” said Syngenta field technical manager Georgina Wood. “There’s a greater chance conditions will be drier. We have been looking to assess the impact of this on pre-emergence performance using cricket covers.

“The sequencing approach, to use a follow-up peri-em application around three weeks after drilling and pre-em treatment, has proven highly successful. It spreads the inherent risk of relying on just one heavily stacked pre-em application, and limits any potential for crop phyto effects.”

In high weed burden situations the work had showed sequencing of actives delivered significantly better control compared to a pre-em stack alone across all establishment techniques. It has proved especially beneficial in min-till establishment systems, where weeds had continued to emerge from depth over time, she added. 

However, Georgina pointed out that for later drilled crops, from the end of October, growers were more likely to err on the side of a single bigger pre-em stack, since the opportunities to get back on with a peri/post-em treatment could be limited, especially on heavy land. Ultimately, moisture and a good seedbed are crucial to ensure reliable performance of residual chemistry.

“The great advantage of successive years’ results on one trials site, to investigate multiple approaches to integrated grass weed control, is that we now have a huge matrix of results and practical ideas to share with growers, which they can try out on their own farms, in their own situations.

“Establishment technique clearly has a significant impact on grass weed populations; it has shown growers and agronomists might need to be flexible in adopting different options to manage serious situations,” she advised. “With direct drilling, for example, the effects of crop residues have been seen to have up to 20 percent impact on herbicide performance, resulting in effects on crop yield.”

Cultivation impacts

Among the many different aspects on trial at Barton, cultivation technique impacts on black-grass seed banks and emergence are a key feature and this year their effects have been monitored in Shabras winter wheat plots (drilled 25th October 2018) following winter wheat and winter barley the preceding years. The herbicide treatment across all plots included a pre-em of Defy + Crystal + DFF on the 1st November.

“Where we ploughed to a depth of 20–21cm in (autumn) 2017 and then intentionally ploughed lower at 27cm in autumn 2018, everything we buried in 2017 we brought up again and, as a result, the control of black-grass was poor,” explained Georgina.

“It demonstrates that ploughing is not always the answer and, if you keep ploughing, then it’s not going to work where black-grass is a problem.

“If you are going to do a first plough after a long time, then go deep and, in subsequent years, cultivate shallower,” she said.

Where direct drilling in 2018 followed the plough in 2017, there was little return of black-grass seed which had initially been ploughed down. Direct drilling left the seeds on the surface and black-grass control was good in both the treated plots (where the herbicide had worked well) as well as the untreated.

Min-till woes

Georgina Wood shows the size of a single black-grass plant established on barren land with no crop competition, compared with (below) a significantly smaller black-grass plant found in the neighbouring winter barley plot

Where min-till in 2018 (to a depth of 15cm) followed the plough, it was clear that the black-grass seed bank had been stirred up again, however min-till following min-till has proved even worse, said Georgina. “What we see in this instance is a disaster in terms of black-grass management. Despite the chemistry applied, seeds are germinating from different depths throughout the top 15cm of soil, making germination time less uniform and control with chemistry more difficult. 

“Min-till establishes wheat well and so it’s a strategy growers have adopted – it’s robust and reliable, but that’s only half the problem. They see good crop establishment but then the black-grass comes with it,” she stressed.

Where direct drilling followed min-till, the untreated plots looked similarly poor. “The herbicides have certainly worked in this scenario although the direct drill establishment is not as good as the min-till.

“This is an area we need to get better at,” she added.

According to Georgina, ploughing in 2018 following min-till in 2017 inverted a seedbed which had black-grass seed spread throughout its profile transferring some of the lower seed bank back up into the germination zone. If growers are looking for a ‘re-set’, they should follow a plough with a spring crop for the best opportunity to take out black-grass.

“Direct drilling, when everything is left on the surface, followed by a plough and good bury is a typical reset. The earlier you plough following a winter crop the better – working it into a good seedbed early to get the black-grass to grow, and provide an opportunity to spray it off,” she said.

“No one cultivation system is the answer – it’s about knowing where the seed is in the soil profile and using the kit you’ve already got to get the job done.”

Crop competition

The competitiveness of winter barley was highlighted in a visual demonstration at Barton alongside wheat and also a barren plot where no crop was planted.

Bazooka hybrid barley was direct drilled last autumn and received the same base herbicide programme as the rest of the field, but increased crop competition from the hybrid barley had reduced black-grass development. “This demonstrates the strength of hybrid barley compared with wheat – it’s much more competitive against black-grass said Georgina who claimed that the extra vigour of hybrid barley in the spring is important.

“The barren patch had the same herbicides but the black-grass plants are huge compared with those in the barley, so when we talk about the importance of crop competition – this is what we mean.”

In terms of spring barley, she pointed out that most are growing it to reduce black-grass on their farms but if it’s planted too early (in the autumn for example), black-grass will compete, the barley will be shorter, more open and allow greater weed populations to grow.

“If you are growing spring barley in a black-grass area you will be mitigating the effects of a spring crop by planting it too early,” she said. 

Syngenta has also run a series of trials this year to look at how crops are drilled in more detail, particularly the subtleties of crop competition and the effects of light interception due to increased use of ‘low disturbance’ drills and wider row widths.

Half of the trials area was cultivated with a one-pass Kverneland CLC cultivator prior to drilling second wheat on the 21st October last year, while the other half was direct drilled into stubble with four different makes of drill.

“Where we went with direct drilling, establishment dropped off on average by 14 percent compared with the one-pass cultivated area,” explained Georgina, adding that it was “a big drop-off.”

“However it’s not all about establishment,” she continued. “Ultimately it’s also about tiller numbers, ear counts and then yield, but direct drilling is an important aspect on farms and we need to find out how to do the best job with it.

“So if establishment was 14 percent less, do we need more seed/m2 to achieve the same result as the cultivated half?” she questioned.

Row widths between 12.5 and 31.0cm were all included in the trial with single row (disc) and band formats as well as varying spacing of seed within the row, over a wide range of seed rates.

“The advice for seed rates is potentially different based on row width but is it right to increase the seed rates on wide rows?” said Georgina. “There are positives and negatives for wider row widths; with more airflow there is the potential for less disease and better trash management, but wider rows with more plants can mean that early season light interception is not so good.

Row width trials were a feature at Barton in 2019

“Wide rows also let more light in for black-grass to germinate which can then tiller wider because of the space,” she added.

“When looking at 25cm row widths, we saw very little difference in establishment between 450 and 225 seeds/m2. However, when the rate was reduced to 125 seeds/m2 there were clearly gaps down the rows and this is likely to have an impact on yield.

“We also looked at high extremes of seed rates, comparing 600 and 800 seeds/m2,” continued Georgina.

“It’s not just about getting the number of ears. There were notably fewer ears with 200 seeds/m2 compared with 600 seeds/m2 but a lot of the ears at the higher seed rate were smaller, and this could mean that quality is affected too.

With 800 seeds/m2 plant flag leaves were much smaller than 200 seeds/m2 and it shows that we are stressing the whole crop. It is competing with itself at high seed rates and can’t compete against the weeds as well.

“These are extremes of seed rates and we are showing that on a wide row width, just upping the seed rate is not always the answer as current advice suggests.”

  • Written by: Farmers Guide
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