The development of glyphosate resistance in Italian ryegrass (Lolium multiflorum) is progressing statistically with the high use of chemical herbicides and has now also reached the UK .

The large number of herbicides still authorised in the USA, and even more so the significantly reduced range in Europe for good reasons, no longer offer any simple solutions. Therefore, the use of Italian ryegrass in green manure and arable grass must be reconsidered and innovative methods must be quickly included in the plant control toolbox.

In Kent, UK, an Italian ryegrass resistant to glyphosate was found for the first time in 2024. (Link)

This discovery shows that the number of resistances ultimately increases with statistical probability when very high levels of individual herbicides are used. Furthermore, the case shows how problematic the use of Italian ryegrass in the field, e.g. as a cover crop component, can become in the long term in Europe if it has to be controlled in many arable crops in all circumstances.

In the UK, 4 cases of resistance of Italian ryegrass to 4 other herbicide classes were already known prior to the discovery of glyphosate resistance (HRAC 1, 2, 5, 15). For comparison: In the entire EU, only 12 cases of resistance to 5 herbicide classes including glyphosate have been detected so far (HRAC 1, 2, 5, 9, 15). The freely accessible international database for herbicide-resistant plants also already documents 6 cases of multiple resistance to 2 herbicide classes each. (Link) Italy accounts for around half of all incidents in Italian ryegrass.

Compared to the USA with a total of 36 resistance events in Italian ryegrass, including 9 against glyphosate, the numbers in Europe are still low. However, this should not be a reason to sit back and relax, because once resistance is present, it will continue to spread needing continuously higher herbicide dosages if resistance management is limited.

Many resistance events have certainly not yet been discovered – but they still exist.

Italian ryegrass is a high-yielding grass that is valued as a green manure and also as a frequently mown arable grass. At the same time, however, it is also a massive weed, especially in wheat, where it can reduce yields by up to 50 %. All 3 areas of use are therefore also points of contact with glyphosate and other herbicides, which in turn leads to the development of resistance.

The risk of resistance development will certainly not be reduced by the further ban on particularly toxic or poorly degradable herbicides (e.g. PFAS herbicide flufenacet).

In Europe, a return to herbicide mixtures with glufosinate (no longer authorised in Europe since 2017), as is currently being discussed in the USA for Italian ryegrass (https://colab.ws/articles/10.1017/wsc.2024.93), can certainly be ruled out. The use of paraquat (banned in Europe since 2009 due to acute toxicity and Alzheimer’s risk) is also recommended there, although there is already resistance to this active ingredient in the USA.

For the control of resistant ryegrass, the electrophysical crop.zone method is an additional tool in the complex control process. Even with the many herbicides still authorised in the USA, this remains a multi-stage process and is becoming increasingly difficult as multiple resistance increases.

 In Europe, there will be an even greater reliance on non-chemical methods without soil movement, which can easily be applied multiple times. This applies in particular if ryegrass is also to be controlled on field margins and in clearance areas.

Good and rapid rooting of the soil with cover crops can also be achieved with phacelia, for example, especially in more complex mixtures that are beneficial for the soil and biodiversity. Increasingly, completely grass-free or at least low-grass green manure mixtures are also available on the market for various applications.

These mixtures are also even more suitable for the crop.zone electrophysical crop protection method. This means that the use of glyphosate can generally be further reduced or avoided. Among other things, this also further reduces the risk of resistance to glyphosate.

Neither lower application rates of herbicides nor spot spraying are suitable for controlling resistance in pre-sowing treatments.

In the field of arable grass, crop.zone is working on combination methods to minimise multiple soil movements when using glyphosate-free arable grass.

This is because soil health and a sustainable yield depend to a large extent on the soil only being moved when absolutely necessary. For all these challenges, crop.zone is an innovative and residue-free tool that opens up new perspectives.