Blackgrass resistance to key herb-icide Atlantis is increasing, according to the latest figures from the Weed Resistance Action Group.

Plants resistant to the chemical were detected on 81 farms across 19 counties by 2006, says Stephen Moss of Rothamsted Research. That’s considerably higher than 2005 when the problem was found on 24 farms across 11 counties.

Some, possibly most, of the resistant populations are due to target site resistance to ALS (sulfonylurea) herbicides, rather than enhanced metabolism, Dr Moss reports.

Testing carried out by Rothamsted Research, Bayer CropScience and Syngenta detected a high proportion of populations showing double-target site resistance they also showed resistance to cycloxydim, an ACCase inhibitor. “This demonstrates that two different resistance mechanisms can occur in the same plant,” says Dr Moss.

Higher risk

RESISTANCE SITES IN THE UK

Both types of resistance are known to pose a higher resistance risk than other modes of action. While there’s no cause for alarm, Dr Moss warns that the widespread target site resistance to fops and dims shows what could happen to Atlantis and other sulfonylurea herbicides.

“We need to think about the long-term consequences of using these graminicides,” he stresses. “It is worrying that three-quarters of the Atlanti-resistant populations show high resistance to fops and dims.”

Gordon Anderson-Taylor of Bayer CropScience agrees. “We are monitoring the situation and communicating with growers.”

He adds that surviving Atlantis-resistant plants were found in less than 0.1% of the area treated.

“Even where Atlantis-resistant individuals have been found, the level of control achieved overall was usually very good.”We’ve seen more cases in the past year, but that could be because of the late timing of some Atlantis applications last spring.”

Control

Early applications are best, in terms of blackgrass control and resistance management, says Dr Anderson-Taylor. He also believes pre-emergence herbicides help protect Atlantis. “Putting more emphasis on effective pre-emergence herbicides is important, as is the use of integrated control programmes.”

WRAG chairman James Clarke says the figures confirm the risk is high and increasing. “Growers must take resistance management seriously. Not only are there few new active ingredients coming along, there’s the prospect of fewer existing ones being available. Protection of existing valuable actives is essential.”

TAG agronomist Bill Barr is not surprised by the WRAG figures. “Bedfordshire and Northamptonshire are some of the worst places for blackgrass. Resistance to fops and dims was found early in this area, so it was a possibility that the same would happen with Atlantis.”

WRAG ADVICE
  • Be aware of resistance risks – do the resistance risk audit
  • Investigate poor grassweed control
  • Collect seed samples in July for resistance testing
  • Use cultural control measures and lower-risk herbicides
  • Consider pre-emergence herbicides in winter cereals
  • Visit the government pesticide site for advice

 

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