Blackgrass resistance poses real threat to UK cereal production, say growers

Grassweeds could start to dictate the way that land is farmed unless action is taken now.

That was the stark message arising from a recent grower survey, representing about 50,000ha of winter cereals, commissioned by Syngenta. The aim was to establish an up-to-date picture of grassweed resistance on farm and to find out whether it was likely to affect cropping and agronomy, says Syngenta’s Simon Parker.

The survey is part of the company’s Grassweed Ultimatum, a new initiative to encourage winter wheat growers to act against the growing problem of grassweed resistance.

“The loss of IPU and trifluralin, together with the spread of resistance and the lack of new chemistry in the pipeline, have concentrated minds and made the industry look for alternative solutions,” he says.

“But we didn’t have the same level of information about growers’ understanding and their future intentions. So we conducted a survey of larger arable farms to get an accurate picture.”

Not surprisingly, blackgrass was the weed identified as having the biggest resistance problem, with 85% of the respondents nominating it as the most difficult grassweed to control. It was followed by ryegrass, and then annual meadowgrass.

But the more shocking revelation was the number of farmers who believed that blackgrass resistance could get to the stage where it undermined the sustainability of winter cereal production.

Over 70% said that without any changes to farming practices, the future of winter cereal production was uncertain.

Even more (89%) said changes in blackgrass control methods were required. “This demonstrates that there is an awareness of the problem at the farm level and that growers are not simply sticking their heads in the sand,” comments Mr Parker.

“The fact that they are open to ideas and are looking for help is a very positive sign.”

The loss of IPU was seen by most of the survey participants (90%) as a further risk to the future use of sulfonylureas. Without its different mode of action, the sulfonylureas were considered to be more exposed to the development of resistance, due to greater reliance on them.

Indeed, 31% of the survey respondents said they were already seeing resistance to products like Atlantis on their farms.

“Most of the growers we spoke to expected to see widespread resistance to sulfonylurea chemistry within five years,” reports Mr Parker. “But around one-third of them were already experiencing it and just over a half predict there will be a major problem within two years”

That ties in with previous experience with products such as Lexus, he adds. “Lexus was launched in 1996/1997 and by 2003, resistance was widespread. Six years appears to be the lifetime of such herbicides.”

Atlantis came along in 2003, which is why it is so important to protect it, he says. “We must keep it going beyond six years. Greater use of pre-emergence herbicides, together with a programmed approach to grassweed control, will help.”

Growers were asked about the best ways of protecting such chemistry. Top of their list was the greater use of non-chemical control methods, next came spraying when weeds are small with mixtures and third came the use of pre-emergence herbicides to reduce pressure.

“Although cultural control methods came out on top, there was good realisation about the value of pre-emergence herbicides, both for the control of weeds and for their ability to sensitise plants.

“The other valuable insight from this was that growers intend to use sulfonylureas in the autumn and in mixtures, which ties in with best practice advice.”

The survey also showed that anticipated levels of control from pre-emergence herbicides were between 60 and 80%, with nearly half of the participants expecting results in this range.

“Interestingly, there were a number of growers who expected to get 98% control,” says Mr Parker. “That’s a realistic target for the whole blackgrass programme, but not for pre-emergence treatments alone. So some expectations are too optimistic.”

But overall, the survey results showed that growers are aware of the grassweed resistance threat and are starting to think differently about how to tackle the problem, he adds.

“The fact that some of them mentioned switching to spring cropping as a remedy where resistance is widespread shows how the situation is developing. They are being very realistic about the threat and are prepared to make changes to protect the valuable chemistry they have.”

He believes that the appropriate use of cultural control methods and pre-emergence herbicides this autumn will make a difference. “It’s also important to get the most from any herbicide treatment, by using the right application technology.”

Case Study – Alswick Hall Farms

Atlantis is still working well for Hertfordshire farm manager Ian Gray, but like many other growers, he is not taking anything for granted.

Mr Gray adopts a three-pronged attack on the weed at Alswick Hall Farms near Buntingford, making good use of cultural control techniques and rotation, while also alternating his use of different pre- and post-emergence chemistry.

Enhanced metabolism resistance has been confirmed on the farm and Mr Gray has his suspicions about target site resistance in a 6ha field, which had serious blackgrass control problems last year.

“I’m getting the seed tested. Knowing what you’re up against is important when it comes to planning a control programme.”

Farming 800ha on heavy land, he grows oilseed rape, wheat, beans and oats, using the plough on land going back into cereals. “It definitely helps with grassweed control, but it also has a soil-conditioning benefit.”

Otherwise, cultivations are done with a Vaderstad Topdown, which Mr Gray describes as true minimum tillage rather than scratch tillage.

Where time allows, stale seed-beds are used to deal with the first flush of blackgrass. “That tends to be before our second wheats, as we have more time to ensure that we’re getting the technique right and seeing the benefits.”

His first wheats are drilled in the second and third weeks of September, while the second wheats go in during the first two weeks of October.

Pre-emergence herbicides are used as a matter of course, with very good results coming from Defy mixes in the past two years.

“We used a Defy/Crystal mix on a large percentage of our wheat in 2007/08,” he recalls. “And the results were very good indeed.”

Last year, he applied a full-rate Defy/Liberator mix across the whole farm. “Again, the results were excellent. Having more than one mode of action in the mix is important.”

His preference is then to use Atlantis in the spring, to control the spring flush of wild oats as well as any remaining blackgrass.

“Our blackgrass control costs are high,” admits Mr Gray. “But we are getting good control by using all the options. We will also be growing spring beans this year, so that any late germinating blackgrass can be dealt with by non-chemical means.”