Getting crops off to a clean start is vital in the pursuit of top yields. Over the next eight pages we relay the latest advice on autumn weed control, starting with what will be the top priority for many growers with blackgrass – maximising Atlantis efficacy. Mike Abram visited Agrovista trials to get the latest advice

Predicting whether a particular day will be the one when Atlantis will work less effectively is virtually impossible it seems. Which makes it all the more important to make sure that as many of the little things that can make a difference are done correctly, Mark Hemmant, technical manager for Agrovista stressed.

Those included using a strong pre- or peri-emergence treatment, applying the product in the autumn if possible, and looking carefully at nozzle choice, he said.

A new liquid formulation of Atlantis, being marketed as Horus by Agrovista, shouldn’t affect performance, the trials suggested (see panel).

The firm’s blackgrass trials at Maidwell in Northamptonshire had three main objectives, Mr Hemmant explained. “We’re looking to find what are the best products to apply, the best timing for them and the best way of applying them.”

The first two objectives were mainly met by conducting traditional small plot trials, while the latter was achieved through the use of a sprayer on a quad-bike, which more closely mimicked farm sprayer applications.

This year’s trials had again demonstrated that autumn Atlantis treatments ran much less risk of poorer performance, he said. Atlantis had been sprayed at regular intervals from just after the crop emerged, when it was difficult to see emerged blackgrass, to April.

The very earliest application had done a reasonable job, giving 97% control when following an effective pre-emergence spray, he noted. “It was too early, but it had done surprisingly well. We’re not recommending spraying before you can see blackgrass, but this should give confidence that you can start earlier than you perhaps think.”

Indeed the later October timings suggest that applying Atlantis from the one-leaf stage wouldn’t be too early, with control reaching 99% following the best pre-emergence treatments.

“If the blackgrass is there [at one-leaf] I’d spray it,” Mr Hemmant said. “It does need to be with a residual, but by starting earlier it could let you get more acres sprayed in the autumn.”

That was important because failures in the spring tended to be more spectacular, he pointed out. “And a failure in the autumn is pretty unusual, whereas it is not so much in the spring.”

The optimum timing remained at the two- to three-leaf stage of the blackgrass, the trials showed, giving 97-98% control without any pre-emergence treatment. “This year it worked really well throughout November.”

The December application illustrated the importance of a pre-emergence spray to help mitigate against any drop in control. “In December there was a bit of a wobble, control dipping to under 75%, but with a good pre-emergence we managed to maintain a decent level of control.”

That drop-off in control was probably because of the colder weather slowing growth, Mr Hemmant believed. “It had been cold for quite a period beforehand.”

Choosing the right mixture partner in that situation could help maintain efficacy a bit better, he added. “In previous years we’ve seen better results in cooler weather from clodinafop where there isn’t any target-site resistance to fops and dims.”

Spring applications in the trial ranged from excellent in late February (99%) to pretty poor in April (54%). “It clearly isn’t just soil temperature dependent,” Mr Hemmant observed.

Indeed soil and air temperatures in late February were below 6C, he noted. “Clearly at that time the blackgrass was actively growing, but it’s not always easy to see or know that.”

In April it was very dry which might have been affecting growth, despite warmer soil temperatures. That combined with larger blackgrass size probably accounted for the poorer result from the timing, he suggested.

“There is clearly also a yield penalty from delaying – in our trials it has been about 1t/ha for every month delay after January in moderate blackgrass pressure.”

It is not just application date that is important with Atlantis. The spray application itself can make a huge difference, too. In three years of Agrovista trials Atlantis sprayed with different nozzles varied in control from 50% to 99%, he noted.

“In the first year the finest sprays were giving the best results. Last year it was Syngenta’s potato nozzle, which is a more coarse (red) nozzle that was best.

“We think that might have been because of less drift. If it doesn’t hit the target it isn’t going to work so well.

“This year the flat fan blue nozzle is against the best overall – over the three years is has been the most consistent nozzle.”

Angling that nozzle 30° forward had also shown a benefit, he said. “Our best application advice is to use a blue 03 flat fan nozzle angled forward and spray at 10km/h.”

Leaf Wetness

Agrovista had also attempted to investigate claims that leaf wetness at application could affect Atlantis performance by simulating those conditions in its trials.

Unfortunately the application date – 12 November – was one where Atlantis worked very well, Mr Hemmant noted. “So there wasn’t any difference. If you could predict days when Atlantis was going to work well it shows spraying onto a wet leaf is not a factor, but on days when it is affected I think this can be a factor.”

Replacing trifluralin

Diflufenican could replace the no longer approved trifluralin in pre-emergence residual mixtures, Mr Hemmant said.

By mixing 0.3 litres/ha of Firebird with 2 litres/ha of Trooper, growers would be applying a full rate of flufenacet plus pendimethalin and DFF. In trials that mix had given between 5 and 10% improvement over full rate Trooper.

“It will cost a bit more, but clearly you can’t use trifluralin this autumn, and DFF could replace it.”

Atlantis available as a liquid

A new formulation of Atlantis, being marketed as Horus and Hatra by Bayer CropScience, will offer growers a liquid form of mesosulfuron-methyl + iodosulfuron-methyl-sodium, in addition to the granular Atlantis formulation.

But the formulations are identical in terms of performance, according to the firm’s Gilles Chevallier. “In some trials the new oil dispersible (OD) formulation is better than the WG, in others the WG is better, and in the vast majority there is no difference.”

So why introduce a new formulation? According to Mr Chevallier there are three reasons for the introduction. “One, to give more choice to the farmer. We’ve done a survey where some farmers have told us they prefer a liquid, while others prefer a granule. With this introduction we will be able to address the different segments.

“The second reason is to secure the supply of mesosulfuron so farmers always have access to the actives. The best way to do that is through the introduction of new products and developments.

“And the third reason is that we believe it gives us an opportunity to remind growers to pay more attention to spray technology and application to get the best out of the actives. When Atlantis came along it was so good that growers didn’t necessarily use it in the best way, but now blackgrass is tougher. This gives us an opportunity to tell growers to pay attention to water volumes, nozzle choice, boom height and forward speeds.”

Those were the type of trials Agrovista were conducting at their trials site. “The benefit we see is you are able to play tunes around application more than you can with Atlantis,” Mr Hemmant said.

“If you want a finer spray you can’t engineer out drift with a three-star nozzle without affecting efficacy. You can manage drift with Companion Gold, but it is not compatible with Atlantis. It is with Horus though.”

In the trials there had been a benefit in mixing Horus with Companion Gold when using a 03 flat fan nozzle at 100 litres/ha at 3 bar and a forward speed of 14km/h. “It is allowing you to use a finer spray, manage drift and not lose efficacy compared with spraying with the same nozzle at 150 litres/ha and 10km/h,” he explained.

“On large estates being able to cover more area in a day might mean you can spray more of the blackgrass area in the spring and be less likely to have a failure in the spring.”

Mr Chevallier wouldn’t be drawn on whether the two formulations would be priced differently to farmers.

Active ingredients

• Atlantis – mesosulfuron-methyl + iodosulfuron-methyl-sodium
• Firebird – flufenacet + diflufenican
• Trooper – flufenacet + pendimethalin