Knowledge Hub Article

The Changing Grassweed Threat


Brome and Italian ryegrass infestations have been growing notably faster than black-grass in recent years, reveals a state-of-the-nation grassweed study. Wild oats are only slightly less problematic than they used to be. And couch remains an issue across a surprising area.


Paralleling  similar work in 2000, the study undertaken over the past season by Monsanto with almost 400 UK growers shows black-grass problems now affecting just under half the winter cereals area against around a third previously. While brome and Italian ryegrass continue to affect relatively smaller proportions of the national winter cereals area, both these problems  have grown more substantially than black-grass over the years (Figure 1).

While wild oats are less widespread than they were in 2000, they still present a particular threat for many growers. At the same time, couch problems certainly haven’t disappeared.

Unveiling the findings at the launch of a special initiative to help growers and their agronomists regain control of grassweeds, Monsanto technical manager, Barrie Hunt pointed out that even in the less affected areas of the west and north, black-grass is now a problem on an average of between 23% and 41% of the winter cereals area.

Brome and Italian rye-grass are most problematic across southern, western and northern counties, while wild oat and couch problems are remarkably consistent across the country.

 “Herbicide resistance is seen as the most important factor behind increasing grassweed problems,” he reported. “In total, over 80% of growers are experiencing black-grass resistance problems, with nearly two thirds rating these as serious or very serious.

“Problematic on more than 90% of farms in central and eastern England, black-grass resistance remains noticeably less widespread in other parts of the country. “However, even in the north and Scotland, two thirds of growers are encountering some resistance problems with nearly 40% of these rating them as serious or very serious.

“At the same time, more than 40% of growers overall and nearer 50% in the west and north are reporting herbicide resistance problems with ryegrass.” 

The increasing difficulties being caused by grassweeds are clearly reflected in the changes the Monsanto studies have recorded in both chemical and cultural control practices over the years.

Back in 2000, autumn post-em spraying was the overwhelming chemical control priority for black-grass, with only minorities of growers employing spring post-em, autumn pre-em or stubble pre-planting sprays. Today, though, the primary emphasis of chemical control has swung emphatically to stubble pre-planting and pre-emergence treatment (Figure 2).

In parallel to this, alongside the workload-drive decline in ploughing, there’s been an equally big swing to stale seedbeds, delayed autumn drilling and spring cropping for cultural grassweed control (Figure 3).

“Our latest study shows growers are employing an average of 2.4 sprays a year to control black-grass,” said Barrie Hunt. “This rises to 3.0 per year where resistance problems are serious or very serious, with greater emphasis put on all spray timings, particularly stubble pre-planting and autumn post-emergence.

“The average winter wheat herbicide spend is currently £89/ha, with a third of growers spending over £100/ha and more than one in every 10 over £125/ha. Growers with the most widespread black-grass problems are spending an average of £109/ha compared to £63/ha for those with few, if any, problems.”

In addition to rotational ploughing, stale seedbeds, delayed drilling and spring cropping, a large number of cultural practices are now being widely used to control grassweeds. These include increased seed rates, more competitive varieties and longer rotations as well as spraying-off infested crop areas and hand-rogueing.

On average, growers are using 6.25 of these techniques, with 45% employing seven or more and 12% nine or more.

“Growing more spring crops, improving stubble weed control, drilling more winter wheat later and improving weed control in winter OSR are the most popular management changes being considered to address grassweed problems,” noted Barrie Hunt.

“Using higher wheat seed rates, increasing break cropping, reducing second wheat growing and greater use of rotational ploughing are also on the agenda for a quarter or more of managers, underlining the extent to which problem grassweeds are now becoming the key management driver for so many farms.”



An innovative on-line resource has been launched this summer to bring the best available industry intelligence together to help growers regain control over their most damaging grassweeds. 

Developed by Monsanto specialists with weed authority, Dr Stephen Moss, Grassweed Action ( provides well-researched, practical frameworks for regaining control over black-grass, Italian rye-grass, bromes, wild-oats and couch that can be implemented by growers and their advisers in ways which best suit their own farm conditions and circumstances.

The free-to-use resource is built around three keys to success in modern grassweed management – understanding, commitment and flexibility.  It includes a knowledge hub providing the best current understanding of each weed, a newsroom offering the latest control intelligence and advice, and a growing network of industry links for extra information, guidance and support.

A special Grassweed Tracker allows growers to rapidly and effectively benchmark their grassweed position with other farms in their area.