After Italian ryegrass with resistance to high rates of glyphosate was discovered on a Kent farm earlier this year, it was zero-till systems researchers pinpointed as particularly at risk.

They found a strong link between farms adopting reduced levels of cultivations and more spring cropping, and an increased risk of glyphosate resistance developing.

While spring cropping is typically deemed good practice for weed management, ryegrass can germinate 365 days of the year, making it much more persistent than weeds such as blackgrass.

See also: 4 reasons Italian ryegrass is a growing threat to arable growers

Flex-till farming 

By springtime, especially in the absence of cultivation, any Italian ryegrass weeds that emerged over the winter are usually well established when cover crops or stubbles are given a dose of glyphosate.

This, combined with the grassweed’s genetic propensity to develop resistance to herbicides, has created the perfect storm for the herbicide’s downfall, meaning no-tillers may need to resort to light cultivations.

Hutchinsons technical manager and cultivations expert Dick Neale is increasingly promoting the idea of “flex-till” farming because he believes it is very difficult to get consistently strong control of Italian ryegrass just by using a chemical approach.

“I’m not saying you have to use aggressive cultivations, but whipping across the top with something slightly more than a rake to pull out established grassweeds and leaving them on top to desiccate will help stop weeds getting out of hand over winter,” he says.

However, he acknowledges it does make it difficult to put a cover crop in, but if farmers put themselves in a position where they are totally reliant on glyphosate, they won’t be able to grow a crop as it will be overridden with weeds.

“If you’re sowing a winter cover crop, to get the best establishment you tend to drill it in August.

“If you then have August-germinating ryegrass coming up in that cover crop, by the time you get to mid-January or February, those ryegrass plants are monstrous, multi-tillered plants.

“The only thing you are then using to control those plants is glyphosate, and that’s the problem,” says Dick.

Italian ryegrass does not respond to cultural controls like blackgrass does, so stale seed-beds, delayed drilling and use of spring barley are simply not as effective.

Its growth habits make it very difficult to pinpoint when to apply both contact and residual herbicides.

“If the weed isn’t all there on the day you spray, or you can’t thoroughly hit it, control will be poor.

“This selects for resistance because you’re not always hitting the emerging population with a sufficient dose of herbicide,” explains Dick.

“The weed then metabolises the herbicide because it’s not at a full effective dose, so that plant becomes resistant over time.

“The rate at which Italian ryegrass develops resistance is off-the-scale fast compared to blackgrass or wild oats.”

Targeting cultivations

Adas principal consultant and weed specialist John Cussans reiterates that the reintroduction of targeted cultivations for mechanical weed control does not have to mean unpicking the positive work done in going no-till.

“We are not saying start ploughing everywhere, but there comes a point with weed management where more movement of soil is necessary,” says John.

“If you see Italian ryegrass surviving in sown crops after glyphosate applications, you must tweak the system and include some cultivation, whether that’s after harvest or before you drill.

“It doesn’t have to be every year, everywhere, but it is a really important part of weed management.”

However, John highlights this should be on a case-by-case basis.

“An absolute zero-till system is fine if you do not have weed issues, but be mindful that when you are using a drill that’s purpose is not to move soil, you are totally reliant on glyphosate.”

Where glyphosate is used, John reminds growers to stick to stewardship guidelines.

“Firstly, make sure you’re using the right glyphosate rates.

“If you have a lush cover crop, the first application of glyphosate is mainly going onto the cover and you’ve effectively got a low dose going on the grassweeds underneath, so take that into consideration,” he says.

“We know there are also conditions such as very cold or waterlogged soils where weeds aren’t growing and glyphosate isn’t as effective.”

He also warns those drilling “on the green” to be wary if they have weed issues. Where there’s grassweeds, John discourages drilling on the green until weeds are combated.

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In-crop herbicides

Resistance to glyphosate and resistance to in-crop herbicides are not the same, so it is unlikely a grower would have weeds resistant to all herbicide modes of action.

To understand how to get the best possible results from herbicides on individual farms, John encourages growers to carry out resistance testing, which is widely available through organisations such as Adas.

“Resistance to residual in-crop herbicides is much more common than glyphosate resistance so test for that first. The two types of resistance are not linked, so it’s important you understand which herbicides are going to contribute best to overall control,” he explains.

“If you see a pattern of glyphosate not working as well as it should, or patchy clumps of Italian ryegrass survive particularly in no-till systems, consider glyphosate-resistance testing.”

The rate at which Italian ryegrass has developed resistance to glyphosate in the UK is very much a developing picture.

“The more we test, the more we’re identifying troublesome populations.”

He points out just because a farmer doesn’t have a herbicide-resistance problem with post-emergence products, they are not immune to glyphosate resistance.

“Everyone is under threat and needs to be aware of this problem.”