Blackgrass is not going away any time soon and a recent expert Question Time-style discussion aimed to answer the burning questions that need answering to get on top of the arable grower’s number one weed threat.

Despite reports of good control from residual herbicides last autumn, a mild and wet winter allowed vigorous blackgrass tillering and in June, high head numbers appeared in crops across the county.

It has been a stark reminder of the difficulties growers face in getting on top of a weed that is threatening the sustainability of winter wheat production in the worst affected areas.

Delayed autumn drilling and spring cropping have long been established as the two major cultural practices that help make a dent in bulging seed banks and reduce in-crop germination.

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And it is how these two are deployed – and the cultivations that precede them – that will make the most difference and experts at a recent panel discussion agreed that being more reactive to each season will maximise results.

Inflexible rotations

Chairing the Bayer Blackgrass Live event in Peterborough was Essex grower Tom Bradshaw, who noted that inflexible rotations have contributed heavily to the problem and said breaking that rigidity could help to get on top of high weed populations.

“We should judge each field, every year and decide whether it can have a winter crop or a spring crop and then we might be able to manage it [effectively] ourselves,” he added.

Agrii’s agronomy manager Colin Lloyd, who has led the company’s Stow Longa blackgrass trials for 16 years, agreed that in the worse situations growers need to be open to change.

“Growers will say ‘that will ruin my rotation’ and it probably will, but you need to stay in business and you need to beat this thing [to do so]. It is change where change is needed,” he said.

Mr Lloyd added that the diminishing reputation of oilseed rape as a “cleaning crop” complicates matters and it can no longer be relied upon to deal with high seed return situations.

Five-year rotation

He suggested a five-year rotation, with six potential crop options – including a mix of winter cereals, oilseed rape and spring crops – taking into account yield potential, cost of production and margin over the course of rotation.

These can then be introduced at the appropriate time, depending on the blackgrass situation in each field. “We are going to have to mix and match,” he said.

Paul Drinkwater, crop production manager at the Abbots Ripton Farming Company, added that the best rotation is the one that makes you money, but agreed they do need a degree of flexibility.

“Look at every field on its merits and if you have some clean land, you don’t change anything. Where you have a problem though, spring cropping [gives you most benefit].”

Timing of cultivation

While planting the right crop at the right time is critical, choice and timing of cultivations can have a huge impact on the success of blackgrass control strategies and ideally growers should be flexible enough to adapt accordingly.

Work at Agrii’s Stow Longa trial site has shown rotational ploughing to bury seed and “reset” the system, followed by four years of shallow cultivation gives the best results and potential extra income of £360/ha a year from improved blackgrass control alone.

However, Bayer’s development manager Gordon Anderson-Taylor reaffirmed the importance of knowing where blackgrass seed is through the soil profile.

“That is the challenge – is it at the bottom, is it mixed through the profile or is it on the top? There have been cases where growers have pressed the ‘reset button’ too quickly and come unstuck,” he added.

Rotational ploughing

The quality of rotational ploughing, if deployed to bury blackgrass seed, was also considered crucial to its success, according to Buckinghamshire-based AICC agronomist Andrew Cotton.

With deep one-pass cultivators largely taking over from ploughs in recent years, ploughing skills have been lost and one of his clients is now sending staff on a training course to re-educate them with the skills to make a proper job.

“You can see seams of blackgrass down the field where land has been ploughed badly. If you make a bad job of the ploughing, the field is ‘mullered’ for blackgrass control,” he said.

Mr Lloyd said that where ploughing is used, growers should aim to plough as early as possible – whether delaying autumn sowing or establishing a spring crop – while conditions are good.

“Plough early, plough while its dry and plough well. You should then drill with as little disturbance as possible,” he added.

In the current economic climate, investing in costly kit specifically to control blackgrass is out of the question for some and Mr Lloyd reminded growers they achieve better results with the resources they have.

He pointed to trials using a deep one-pass system – thought to worsen blackgrass in a bad situation by mixing seed through the profile – in a trial establishing winter wheat after oats full of blackgrass.

They were able to reduce blackgrass from 876 ears/sq m to 72 ears/sq m by just shifting drilling date from 30 September into the third week in October.

“You can make a huge difference without changing machinery, but there is no doubt that if you carry on the same way where you have high seed return, moving soil around and popping it in at the end of September, you are on a road to nowhere,” said Mr Lloyd.

It was also suggested that various establishment systems can be made to work for blackgrass control, but much will depend upon the farmer and his or her situation.

Mr Drinkwater said there are advantages of no-till, min-till and ploughing, but it’s important growers know their farm and its blackgrass challenges, choose a system that fits and stick to it.

He warned against too much mixing and matching various practices and pieces of machinery from the plethora of conflicting information out there in the industry. “If you do, you will break the system,” he added.

Resistance risk

Some good news in the battle against blackgrass is that there are still no cases of resistance to the broad spectrum herbicide glyphosate in UK weed populations, including blackgrass.

Mr Cotton said the risk is there, however, and acknowledged recent Adas research looking at glyphosate resistance and how to combat its development.

“The takeaway message is to avoid lower rates and if in doubt [about control], treat again. You should also avoid using the product if no subsequent cultivation is to take place,” he explained.

Mr Lloyd favours just one application before drilling, with repeat flushes and applications of glyphosate having little effect on large seedbanks and also fanning the flames of resistance.

“We need to limit the amount of glyphosate we use and use it wisely at sensible rates,” he added.

Rothamsted Research resistance expert Richard Hull added that another key blackgrass killer, residual pre-emergence active flufenacet, saw less than 1% per year decline in efficacy after reviewing manufacturer data between 2001-14.

“The risk is there, but it’s low risk like most other residuals. It isn’t working quite as well as when it was first introduced, but it’s still one of the best actives we have,” he added.

Dr Hull added that enhanced metabolism resistance to ALS-inhibitors such as Atlantis (iodosulfuron + mesosulfuron) could not cross over to other modes of action, such as flufenacet, in recent Rothamsted experiments.

“It appears that Atlantis is only selecting for an ALS-specific non-target site resistance, so there is no difference in control with flufenacet,” he said.

With pre-emergence residuals the most effective chemistry, Mr Lloyd also noted the importance of ensuring growers apply sprays effectively to maximise performance.

“You need to consider where the target is, what you are trying to achieve and choose the right nozzle for the job,” he said.

The Blackgrass Live panel

Chairman – Tom Bradshaw, Farm Manager, Proagri

Andrew Cotton, Independent Crop Consultant, Cotton Farm Consultancy

Colin Lloyd, head of agronomy, Agrii

Richard Hull, research technician, Rothamsted Research

Gordon Anderson-Taylor, development manager, Bayer

Paul Drinkwater, crop production manager, Abbots Ripton Farming Company

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You can watch the Blackgrass Live debate in full by visiting the Bayer website