Ryegrass spreads fast as new trials target growing UK weed threat

Italian ryegrass is spreading rapidly across UK farms, with new trials launched to tackle what growers warn is an increasingly costly and difficult-to-control threat.

At a demonstration farm near Harwich in Essex, the impact is already stark. Ryegrass populations have surged to as high as 120–150 plants per square metre, with wheat yields in the worst-affected fields falling by up to 60%.

The heavy land site, run in partnership with agronomy firm Hutchinsons, has battled grassweeds for years. While black-grass has largely been brought under control, ryegrass has now become the dominant issue.

Host farmer Andrew Strachan said the shift has been gradual but significant.

“We’ve made great progress against black-grass, and have farmed around 98% of it out,” he said. “But Italian ryegrass has taken over as the main issue, and is proving a lot harder to control.”

Weed pressure has been building since the stubble burning ban in the 1990s, he added, with historic land use also playing a role. Some fields were previously used for ryegrass seed production, while others were orchards with grass beneath the trees.

In response to severe infestations, one field was ploughed and left fallow for a season.

“That field is now one of the cleanest on the farm,” Mr Strachan said.

Targeted cultivations and herbicide applications were used during the fallow period to reduce weed populations before returning to wheat.

Rotational ploughing remains part of the system, used once every seven years within a min-till approach. However, in dry seasons, the weed can still emerge through cracks in the silty clay soil.

The farm is also exploring a range of integrated measures, including alternative cropping, clover undersowing, revised herbicide strategies, improved machinery hygiene and drainage improvements to boost crop competition.

Despite this, complete control remains elusive.

“We’ve made some progress, and the worst fields are getting better, but at the moment, there’s still always some level of seed return, so it’s a question of what’s acceptable,” Mr Strachan said.

Beyond this farm, the issue is becoming more widespread.

ADAS weed science consultant John Cussans said Italian ryegrass is no longer confined to isolated hotspots and is now affecting many parts of the UK.

“Sometimes it is because of an historic legacy, but other times that’s not the case, and it can be hard to pinpoint exactly where issues have come from,” he said.

The growing spread of the weed poses a serious risk to arable productivity and long-term farm profitability.

What makes ryegrass particularly challenging is its biology.

It has a prolonged germination period, with peak emergence in the autumn and another flush in spring, but the ability to emerge throughout the year limits the effectiveness of cultural controls such as delayed drilling.

Once established, plants are highly competitive, forming large, tufted growth that outcompetes crops for light, water and nutrients.

Seed return is also significant. A single plant can produce several times more seed than black-grass, allowing populations to rebuild rapidly even from low levels.

The species is also more tolerant of stress, including drought, due to its Mediterranean origins.

Herbicide resistance adds a further layer of difficulty. Resistant populations have been confirmed across the UK, affecting multiple modes of action including ACCase and ALS inhibitors, as well as flufenacet and glyphosate.

Testing at the Harwich site has confirmed resistance to several key herbicides, including “RR” resistance to cycloxydim, pendimethalin and pinoxaden.

While some chemistry remains effective, early signs of reduced sensitivity are emerging in certain cases.

Hutchinsons development manager Jennie Watson said growers still have options, but these must be used carefully.

“With new chemistry available, there are still plenty of effective options for controlling ryegrass, but the challenge is often the cost-effectiveness,” she said.

“We have to consider how they can be best used alongside other cultural controls.”

The trials are designed to test both chemical and cultural approaches under real farm conditions.

They include 25 different herbicide programmes, variations in glyphosate timing to reflect prolonged germination, and comparisons of cultivation techniques and drilling methods to improve crop competition.

Results from the work will be shared later this year, offering practical guidance for growers.