06 March 2025, UK:How does herbicide resistance occur?
Think of it like natural selection or the survival of the fittest. Some weeds have natural inherited mutations which allow them to survive and reproduce after they’ve been exposed to a herbicide with a specific mode of action. When the weed survives, its seedlings may also carry resistant traits, and the cycle of resistance carries on.
What’s making tackling resistance even more challenging?
Repeated use of products with the same mode of action: Resistant weed populations don’t just survive herbicide application, they go on to thrive, passing resistance onto their offspring, until they become dominant in your field.
Regulation has reduced herbicide options: With the current regulatory system closing the door on new actives coming through, you may find that you’re reliant on the products you’ve always used. This makes tackling resistance even more challenging.
Which weed poses the biggest problem?
When it comes to problematic weeds, blackgrass is the one to watch. This native annual weed can destroy important cereal crops like winter wheat and in many areas of the UK, it’s now resistant to herbicides. Let’s put this into context, research on the impact of resistant blackgrass in different farming scenarios has found worst case if all UK fields had high levels of resistant blackgrass, 3.4 million tonnes of wheat could be lost each year. The economic cost of which would be an eye-watering £1 billion.
Know your chemistry-which products are weeds becoming resistant to?
Weeds are more likely to become resistant to the products you use when they are slightly bigger, because you need more active ingredient to kill them. We call these ‘contact chemistries,’ and ALS and ACCase are the key ones to note in grass weeds.
Tackling herbicide resistance-strategies for success
There’s no one magic way to manage herbicide resistance. Farmers should focus on integrated controls, aimed at reducing the weed population from the very beginning so there are less survivors and there’s less chance of resistance developing in those weeds that do survive. Follow these strategies for success:
Carry out weed mapping: This will help you keep an eye on populations in your field.
Get out in the field: There’s no better way of spotting signs of resistance early. Get some resistance testing done if you notice any issues.
Rotate crops: There are plenty of benefits of using crop rotation to manage herbicide resistance, not least that it disrupts weed growth cycles and allows you to rotate between herbicides with different modes of action.
Make use of mixtures and sequencing: Using herbicide mixtures can kill weeds that evade control following the use of a single herbicide. Sequencing allows you to alternate between herbicides with different modes of action. Both help break the cycle of repeated use of the same herbicide.
For more expert advice on managing herbicide resistance and controlling weeds in cereal crops, click here
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