When it comes to herbicide applications black-grass is a notoriously tricky target. At the one to three-leaf timing - when Atlantis WG (mesosulfuron and iodosulfuron) is most effective - black-grass is only 2-3 cm tall with thin vertical leaves just millimetres wide.
Atlantis WG is a contact herbicide. That means it is absorbed through the leaves of the plant. For optimum effect, spray droplets must hit the target and remain there for at least two hours to allow sufficient uptake by the weed.
Black-grass not only has a minimal leaf area, but it’s hairless and often waxy surface means application technique can make a big difference, according to Phillippa Overson, the combinable herbicide campaign manager at Bayer CropScience. This year’s conditions demand careful attention to detail to optimise efficacy, she says.
“This autumn’s good growing conditions have resulted in thick crop canopies, which make it more difficult for spray to reach its target.
Ms Overson says that by increasing water volume, growers can increase the amount of spray that penetrates the canopy. “For guidance we normally recommend spray volumes of 100L/ha in autumn and 200L/ha in spring. The difference normally takes into account thicker crops going into the spring but circumstances this autumn could justify upping water volumes if conditions continue to promote growth.”
Growers should look to apply post-ems sooner rather than later, advises Ms Overson. As plant size is the dominating factor in the efficacy of post-em, application at the 1-3 leaf stage (GS11 – 13) is crucial for achieving a satisfactory result
AVOID WET LEAVES...IF POSSIBLE!
Try to apply Atlantis WG to a dry leaf and allow drying time. At this time of year that can be difficult, so take a sensible judgment. If the choice is between spraying Atlantis WG after rain but going into dry weather, or applying it to a dry crop with heavy rain forecast imminently, always do the former. Although it will take longer for the product to dry onto the leaf, it’s better than seeing it wash off within just a few hours.
“We’ve tested the impact of different nozzles with Atlantis WG and flat fans are the most reliable and remain our recommended choice,” points out Ms Overson. “That’s not to say on a particular day in the right crop and target other nozzles, or angled nozzles, may do a good job. But where there are different sized black-grass plants or the wind is likely to change direction, a flat fan will give the most reliable results.”
Speed is important too. Bayer recommends 12km/h maximum speed and while variable rate regulators automatically adjust the pressure if you travel faster, the spray quality is affected and with such a small target, it’s not worth the risk. If speed is doubled, pressure is quadrupled and that will turn a fine/medium spray into spray so fine it is off the scale and with a much higher potential to drift. Fine droplets have less kinetic energy and are less likely to go where you intend, you need some weight to get the momentum and the accuracy.
Finally, don’t forget the adjuvant! The most effective to use with Atlantis WG is bioPower; it is a very important aspect of the tank-mix. It helps the Atlantis WG to stick to the thin leaves of black-grass plants and will optimise efficacy.
Remember, at post-emergence you’ve only one chance to hit the target with your contact product. It’s important to make sure you get everything right.