Don’t rush into applying sulfonylurea herbicides until weeds are showing sustained active growth, even though soil temperatures are rising, warns Agrovista technical manager Mark Hemmant.
“In some areas, soil temperatures are about 6C and we are seeing signs of growth, but it’s not active growth,” he says. “Blackgrass is waking up after the winter and it is likely to be at least a week before there is sufficient growth for Atlantis and Horus (mesosulfuron + iodosulfuron) to be effective.”
If warm temperatures continue there is a good chance Atlantis and T0 fungicide applications will coincide at the end of March/early April, he says. “Yellow and brown rust have been spotted and I think most growers will be planning to tank mix Atlantis with a T0 fungicide.”
This is not a problem as long as Bayer’s tank-mix recommendations are followed, he says. “For rusts and low levels of septoria, our T0 of choice is straight cyproconazole and for mildew and eyespot it is Ceando (epoxiconazole and metrafenone).”
These have been biologically tested and are not antagonistic to Atlantis control, he explains. “We recommend these tank mixes with Atlantis.”
Pushing back Atlantis applications means blackgrass will be large and application technique is important, he says. “We recommend 150 litres/ha of Atlantis applied at 10kph with a standard blue flat-fan nozzle angled forward at 30 degrees.” These nozzles performed consistently in three years of small plot replicated trials, he says.
ProCam technical director David Ellerton agrees that waiting for active growth before applying Atlantis is crucial. “You need a settled soil temperature of 6-8C for about a week before applying.”
Most soils are not warm enough, but if the weather holds it might be possible to go next week, he says. “However, don’t be tempted to apply to struggling crops or waterlogged soils.”
Forward crops at late-tillering may require an early T0, which could clash with Atlantis applications, he says. “Ideally, Atlantis should be applied on its own with adjuvant Biopower, but if it can’t be avoided, don’t mix with chlorothalonil or imazaquin products.”
In most situations, there should still be time to apply Atlantis before T0, he says.
AICC agronomist Bryce Rham, from Shropshire, thinks Atlantis shouldn’t be applied until the first week of April. “It’s too cold and I advise my growers to wait; soil temperature has to be 8C and you need a run of warm nights.”
Othello (mesosulfuron + iodosulfuron + diflufenican) could be applied to control annual meadowgrass, but growers who want to apply Broadway Star (pyroxsulam + florsulam) need to wait, he says. “If Atlantis coincides with T0 there are tank mixes you can do, but with Broadway Star you have to go before or after T0.