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13 Sep 2022

Resetting the clock on grass-weed control

As featured in Arable Farming Magazine

Resetting the clock on grass-weed control

by Arable Farming Magazine August 2022 issue

A new mode of action for grass-weed control in wheat, as yet unaffected by cross-resistance, is available to growers this autumn.

New herbicide modes of action are a rarity these days but BASFs active substance Luximo, which recently gained approval for use in the UK, is one, albeit cinmethylin, the chemical behind the Luximo brand, was first discovered back in the 1970s.

Cinmethylin also has the distinction of being the first wholly Chemicals Regulation Division (CRD)-managed active substance to be approved since crop protection regulation was repatriated following Brexit.

BASF launched Luximo in a festival-style event at NIABs Black-grass Centre at Hardwick near Cambridge a weed scientists paradise, where in some areas of the site it can be difficult to spot a crop through the jungle of black-grass.

Luximo has been in development trials in the UK for several years, providing growers and agronomists with an introduction to its potential, but at the launch event there was opportunity to take a deep dive into its performance.

Amid the black-grass-infested plots at Hardwick, a key question was: where does Luximo fit? Is it a product for use only in the highest pressure and most difficult black-grass situations? BASF business development manager Stuart Kevis referenced a large data set, which has under-pinned the herbicides development, to provide the answer.

In a comparison of Luximo with solo flufenacet, taking in 106 trials across four years and in a range of different black-grass situations, from zero to 500-plus black-grass head counts per sq.m at final assessment, Luximo control levels always remained above those of flufenacet, regardless of the level of black-grass pressure, said Mr Kevis.

According to BASF, cinmethylin delivers a control uplift of 20% of both black-grass and Italian ryegrass compared to flufenacet.

The message from us is quite clear; Luximo is not just for your heavy black-grass pressure situations.

It works very well in lower pressure situations as well.

Remember that numbers count; every single plant that you can kill makes a difference in return to the seedbed, said Mr Kevis.

Growers and their advisers will also be keen to hear if Luximos activity is affected by soil type.

According to BASF, four years of trials across a range of soil types - light, medium, heavy and chalk - provide the answer.

The message is the same - Luximo remains above flufenacet across all those soil types, always with an uplift of around 20%, said Mr Kevis.

BASF has also assessed the performance of Luximo against current standard farm herbicide programmes, in a series of 21 trials conducted between 2018-2022.

Performance On the back of results from these trials, the manufacturer concludes that Luximo + pendimethalin (PDM) will deliver a performance comparable to Crystal (flufenacet + PDM) + diflufenican (DFF)) + Avadex (triallate).

So, if you are currently very happy with the performance you get with Crystal + DFF + Avadex you will probably be very happy with the performance of Luximo + PDM, said Mr Kevis.

That is not to say there is no place for Avadex with Luximo.

If you add Avadex, you will also get an uplift, so depending on the situation you have on the farm, Avadex may still add a benefit.

But Luximo + PDM really is a powerful solution going forward.

In the modern era the launch of any new crop protection active substance comes with the warning that it must be used within an IPM approach if resistance is not to significantly compromise its efficacy within a few short years.

BASF head of business development Steve Dennis tackled the thorny issue of what it means to have a new mode of action when target weeds - in this case black-grass and ryegrass - are adapt ed to it.

He highlighted results from a Rothamsted Research study over several years looking at Luximo and its efficacy against different strains of black-grass and ryegrass present across the UK.

The Rothamsted scientists studied more than 100 populations of black-grass from sites across the country, growing-on seed from these populations in glasshouse, pot and small plot trials and evaluating the performance of Luximo and other herbicides against them.

They looked at 18,000 plants, comparing them to the Rothamsted Research standard susceptible population or wild type, which is black-grass that has not adapted to herbicides at all.

Luximo gave 100% control of this population, said Mr Dennis.

At the other end of the spectrum is their standard resistant sample.

This is amongst the most difficult to control black-grass that they have ever found, and they have tried Luximo across that and they are still getting a very good level of control for a residual herbicide, with 86% control.

The average level of control of the 100 populations collected from fields across the UK was in excess of 97%, added Mr Dennis.

But there was also an early warning of the potential for resistance development.

That is a really positive set of results but within the individual populations there are one or two where, even though Luximo was not being used there, we can already see slightly lower performance.

We are talking about a couple of populations out of 100.

Detail A more detailed study conducted by Rothamsted Research to understand what was happening in these populations revealed that consistently good control was seen with the full field rate of Luximo, even in the harder to control black-grass populations.

But as the dose rate was reduced the performance of Luximo started to drop off.

Luximo is a full rate product.

It is a product we should be using properly.

We dont want to compromise its performance.

And it is also a product that we should be protecting because there are indications that although we are controlling all populations well, there is already diversity out there in terms of how well Luximo will work.

We need to protect the chemistry, we need to use it in mixture, we need to use it in conjunction with appropriate IPM techniques, said Mr Dennis.

Further work tested the activity of Luximo against black-grass populations artificially created by Rothamsted Research to be as resistant to herbicides as possible.

Three strains of highly adapted, non-target site resistance (TSR) black-grass were tested, with resistance to flufenacet, PDM and Atlantis (iodosulfuron + mesosulfuron).

The good news is that when we use Luximo at the field rate, the performance is really strong across all of those, said Mr Dennis.

Where PDM was giving 20% control, Luximo was delivering 90% control.

And with control from flufenacet down to 23%, Luximo was still giving close to 60% control.

And most remarkably they have created strains where they are getting zero control from Atlantis but 100% from Luximo, added Mr Dennis.

We have a new mode of action with no direct cross-resistance to other herbicides.

We are resetting the clock here, he said.

Luximo key points

  • Available as Luxinum Plus containing 0.7 litres/ha cinmethylin + two litres/ha PDM delivering 500g/ ha cinmethylin and 910g/ha PDM
  • Application window pre-em up to GS30
  • Recommendation is to apply pre-em to boost grass-weed control
  • Black-grass, ryegrass, annual meadowgrass and poppy on the label
  • For use in winter wheat only
  • Water volume currently 150-300 litres/ha
  • Non-target plant buffer zone applies 5m from cropped land

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