Resistance to Atlantis has been confirmed on 24 farms across 11 counties, according to latest testing results reported by the Weed Resistance Action Group.
Most appear to be at the early stages of resistance development, says ADAS grassweed expert, and WRAG member James Clarke.
“But it is confirmation of the resistance risk and an early warning of the wider potential threat.”
The findings need to be put into perspective, says Rothamsted Research’s Stephen Moss, who collated the data.
“It is a very small number of farms compared with the area sprayed, and most of the sites are not complete failures.
Overall, the level of control from Atlantis is very good in most fields.”
Atlantis has worked as expected in the majority of situations, agronomists are reporting, but there are more cases of slightly poorer control this year than in previous seasons.
ProCam technical director David Ellerton puts the 5-10% of fields falling into that category more down to poor timing than resistance.
“We had a lot more problems with Atlantis at certain timings, particularly when it was applied in late March, early April.”
A couple of frosts during that period, on top of the cold, dry March, meant grassweeds were not actively growing, he says.
“It looks like the weeds didn’t take up enough chemical to kill them.”
The overriding factor in any poor control seen this season has been application timing, agrees Bayer CropScience’s Gordon Armstrong-Taylor.
“Some growers got seriously delayed – weeds were GS32 and beyond.
It is not the time to be controlling blackgrass.
Where applications went on in the autumn control has been good.”
Frontier technical manager Bob Mills has also seen more problems than in previous seasons.
“I’m hoping it is more to do with the weather and timing than resistance, but we will be taking seeds to check.
“From [the WRAG] results it does seem, however, resistance is more of an issue than we thought, although I’m not surprised.
It is worrying and disappointing how soon it has developed though.”
UAP’s Chris Bean wouldn’t be surprised if tests on grassweed seeds from the handful of fields where control has been much poorer than expected do show low levels of resistance.
“My guess is it could be in the background on top of the dip in the performance because of the weather.”
Where resistance is suspected it is important to get a seed test done, Dr Moss says.
“Once you know what you’re dealing with, you can decide on the best herbicide and cultural control strategies.”
The optimum time for collecting blackgrass seeds is the second and third week in July, although where plants have recovered from Atlantis’ initial knockdown growers may have until the end of July.
All three agronomists are advocating more autumn Atlantis use next season.
“Overall, Atlantis worked well in the autumn,” Dr Ellerton says.
“It is clearly better to apply it going into rather than coming out of cold weather.”