With crucial spraying days just around the corner, growers have been urged not to overlook the importance of sprayer set-up and application technique.
Small grass weeds, particularly black-grass, are one of the trickier applications an operator will encounter. Contact herbicides, like ALS-Inhibitors, are effective only when they land directly on the leaf; they need to be applied accurately to get a good result.
“The optimum timing for controlling black-grass, and many other grass weeds, is at early growth stages,” explains Dr Clare Butler Ellis of NIAB-TAG. “Unfortunately, small, vertically standing grass weeds can be difficult to hit with the active substance so application method is important.
"A fine-medium spray from forward-angled nozzles is the most effective in these situations. But be careful – a very fine spray runs the risk of drift, whereas a coarse spray may land in large droplets on the soil and not the leaf.”
Growers are often under pressure to deliver a high work rate during spring, as the next spraying opportunity is never guaranteed, Clare points out. Increasing the speed of travel is the obvious way to up work rates, but be warned – it can affect the quality of application.
“At higher speeds the boom isn’t as stable so the distribution of spray will not be as consistent,” explains Clare. “The balance between maximum speed and a good application depends on the situation. Wider booms have more pronounced effects from instability and uneven ground also causes problems. The aim is for the boom to stay half a metre above the target at all times, so each operator has to judge how best to do this with their equipment.”
As boom stability is important, it’s worth checking that the boom suspension is in good working order well ahead of spraying. “The suspension will make the difference between doing a good job and a really good job,” says independent spray consultant Dr Paul Miller.
“The way to test it is to extend the boom arms completely, then push down at each end in turn and let go. A well-functioning boom will bounce just once before returning to its original position,” explains Paul. “If it bounces more than once, the dampers may need replacing. If it moves slowly, then it may need lubricating.”
Paul also recommends checking and cleaning the nozzles and filters, as any build up of deposits might cause a blockage that could deliver an uneven spray.
“There’s no point losing some of the herbicide’s activity through a poorly tuned sprayer,” says Darren Adkins of Bayer CropScience.
“Growers don’t need me to point out how every percentage point matters when you’re battling black-grass, but application technique is often overlooked as a cause of poor performance in the field.
“For Atlantis WG (mesosulfuron + iodosulfuron), a forward speed of up to 12km/h applying 100L – 150L/ha is the best way to cover as much ground as possible during the day.”
Like Clare Butler Ellis, Darren recommends using a fine to medium spray quality with flat-fan nozzles. “Once the sprayer is ready for action, don’t be too impatient,” he says. “You only get one spray with Atlantis, so make it count.
“Ensure the leaf is dry and there is enough time for the spray to become rainfast before starting to spray.” This can take up to 2 hours after spraying has been completed.