Dealing with the threat of herbicide-resistant grass weeds

“But thankfully, the problems are not as large as those being faced by tillage farmers in Great Britain,” Derek Delahunty added.

“The herbicide resistant blackgrass we have in this country probably arrived on combine harvesters and other items of machinery imported from Britain.”

In order for farmers to deal with problems associated with herbicide resistant weeds, they need to know the extent of the challenge that exists in the first place.

Derek Delahunty again: “This means being able to recognise these weeds in the field at all their growth stages.”

The Lemken representative cites whole cropping as a means of reducing blackgrass infestations.

He said: “It’s an option that can be considered in cereal crops that are at an advanced stage.

“Blackgrass is an annual plant.

“So, taking this approach can help to reduce the weed burden, assuming the crop is ensiled prior to seed set taking place within the blackgrass population that exists.

“Some blackgrass seeds may well survive this process.

“It’s important then to ensure that the dung in which the seeds can be found is not spread back on to tillage ground.”

Putting tillage ground back into grass is another way of controlling blackgrass.

“Cutting silage for a number of years will act to significantly reduce weed population numbers,” confirmed Delahunty.

He added: “Blackgrass is not the problem in countries like France and Germany as is the case in the UK and Ireland.

“This is because farmers in continental Europe can successfully grow a number of crops on the same ground each year.

“In France, farmers will establish a cover crop as soon as they complete the annuakl cerelam harvest, most likely in late June or early in July.

“When it comes to establishing the subsequent winter cereal crops, they chop the cover crop using a front mounted machine with the drill attached to the rear of the tractor.

“This means the freshly planted grains have the immediate protection of the previous cover crop.

“As this organic material decays, it acts as a valuable fertiliser for the newly emerging cereal.”

Delayed planting is another blackgrass control option.

“As soon as fields are clear, following the previous harvest, growers should go in with a light harrow or tine, simply to disturb the top few centimetres of soil,” Delahunty commented

“This encourages the germination of blackgrass weed seeds that are lying close to the surface.

“This process provided very effective weed control options prior to planting the subsequent crop.”

He concluded: “I am very aware that delayed planting is a very weather-dependent option.

“And there’s no doubt that the weather last autumn and the year previous was not working in farmers’ favour in any sense.”

Transitioning to direct drill systems can take up to 10 years

Transitioning to min-till and direct drill production systems can take up to a decade, according to Derek Delahunty.

“And this is very much a gradual process.” he added.”

“Taking account of factors such as the enhancement of soil quality and key physical challenges, including compaction, is at the very heart of this progression.

“Given the complexity of this transition, the full conversion from plough: till: sow to a direct drill based-production system may take varying amounts of time across the different soil and land types that make up a typical arable farm in Northern Ireland.

Significantly, Delahunty, regards ploughing as a critically import technique both at the start of a commitment to min-till or a reset button at any stage thereafter.

He explained: “Historically, the plough was the go-to option when it came to securing effective weed control within Irish cereal production systems.

“And we have to learn from history.

“Chemical weed control systems have only been around for a relatively short period of time, relative to the overall impact made by production agriculture, going back centuries.”

The Lemken representative questions the long-term availability of chemical-based herbicides into the future.

“And this includes glyphosate,” he stressed.

According to the Lemken representative, ploughing will remain at the heart of the agronomic systems practised in Northern Ireland.

He further explained: “But the technique must be carried out properly.

“And this means achieving the complete inversion of the soil being ploughed.

“If it’s a case of only half turning the soil, problems will arise.

“For example, under these circumstances many weed seeds will still have the opportunity to germinate.

“So instead of only having weed seeds scattered on the surface of a field, they become distributed throughout an entire soil profile.”

Delahunty also recognises that climate change is acting to deliver new challenges for tillage farmers when it comes effectively establishing and management crops.

“As ambient temperatures rise, weed seeds will have an opportunity of germinating much more quickly and effectively,” he said.

“Back in the day, farmers would have been able to plough: till and sow their crops.

“The next time they would have visited the fields was at harvest time.

“Obviously this is no longer the case.

“And fundamentally, this is because weed populations are changing their growth habits.

“This reflects their ability to adapt to changing circumstances.”

He concluded: “So farmers here in Northern Ireland must learn from history and change their crop management systems in a corresponding manner.”

Enable Conservation Tillage

Meanwhile, Teagasc is confirming that the challenge of ‘uncontrollable grass weeds’ within crops remains a major challenge for all arable farmers.

This is particularly so, where the use of minimum cultivation techniques, is concerned.

Teagasc’s recent Enable Conservation Tillage (ECT) project was developed to communicate the latest thinking on how these techniques can be applied in ways that respond to the grass weed challenge.

In the past, a number of Irish growers experimented with min-till, direct drill or no till systems, but were unsuccessful.

Many identified the difficulty of controlling of grass weeds as one of the primary reasons for reverting to plough-based systems.

The ECT project, however, highlighted a number of monitor farmers who had successfully made the change.

One of the big take-home messages from the project was the fact that that the establishment system is only part of the puzzle, more integrated pest management (IPM) tools must be incorporated into the farm system for the practice change to work.

According to Teagasc arable specialists, good rotations, avoiding compaction, learning from mistakes and reducing grass weed problems through cultural control methods, as well as herbicides, are all important parts of a successful transition.

Herbicide-resistant blackgrass populations are already creating challenges for Irish tillage farmers.

Experience at Teagasc Oak Park in Co Carlow is already confirming that that blackgrass can become an issue unless growers are vigilant.

In 2020, as part of a plan to increase biodiversity on the farm, wild flower margins were planted.

Significantly, the Oak Park farm manager identified blackgrass plants in one field.

A plan was put in place to eliminate the blackgrass.

Glyphosate was used to burn off the affected margins, multiple stale seed beds were applied and the margin in question was ultimately planted with grass.

Italian ryegrass is another grass weed that is starting to become an issue on many Irish farms.

The problem can be traced to the autumn of 2018 when arable farmers were paid to establish forage crops after harvest to produce much need forage for livestock farms.

Some of this Italian ryegrass has now become a problem with many herbicides struggling to control it.

Farmers have control over their own destinies

Teagasc’s John Mahon has been involved with the ECT project for a number of years.

“We looked at a number of weed types, including sterile bromes, canary grass, wild oats, blckgrass, Italian ryegrass and, latterly in the project, rat’s tail fescue,” he explained.

“We even had some samples of herbicide-resistant annual meadow grass presented to us.”

He added: “All of these weeds are problematic.

“But wild oats and sterile bromes are present on most farms.

“We have control options for these weeds.

“However, with the likes of blackgrass and Italian ryegrass, problems can escalate very quickly.

“Rat’s tail fescue is becoming more predominant in minimum disturbance system.”

Mahon continued: “Farmers need to be doing more when it comes to controlling these very problematic grass weeds.

“For years we have solely relied on chemical control, when it comes to dealing with grass weed problems in Ireland.

“But this situation is changing. Herbicide resistance has become an issue.

“And we are also losing a number of chemistries that were a mainstay of weed control policies up to this point.”

According to Mahon, the growing use of minimum disturbance crop establishment systems has allowed the challenge posed by pace of grass weeds to accelerate.

He concluded: “There is also a need for farmers to better recognise these more problematic weeds at an earlier stage of growth.

“We also need to include more cultural control systems into the future.”

Ploughing represents a re-set button for arable farmers

With the number of agrochemicals available to arable farming fast-reducing, it’s obvious that integrated pest management (IPM) systems will come to the fore when it comes to growing high quality crops.

And it’s in this context, that ploughing will have a vital role to play.

But’ there’s a lot more to ‘turning the sod’ than its role as a weed control option will deliver.

For example, recent research has confirmed that ploughing is not the ‘arch enemy’ when it comes to reducing greenhouse gas emissions within the arable sector.

The reality is that chemical nitrogen fertilisers are the bad boys in this context.

If one works on the basis that ploughing is, pretty much, a carbon neutral activity then one can quickly make a case for its continued use at the very heart of Northern Ireland’s crops’ sector

As that industry looks to the future, one within which the use of herbicides will be strictly limited, it is obvious to me that ploughing will – once more – become centre stage from a soil cultivation perspective.

Over the years, many grass weeds has developed an almost total resistance to selective herbicides.

The only way to minimise the impact of the weed on infected farms is through a combination of cultivation techniques and rotational crop changes.

From a cultivation point of view, the use of min-till or zero-till systems do nothing at all to help the situation.

In fact, they probably facilitate the further growth in blackgrass numbers.

Ploughing, on the other hand, acts like a re-set button.

By burying the likes of blackgrass seeds to depths below which they cannot germinate, genuine control of the weed is achieved.