Article taken from the Farmers Guardian
Spray application technique can have a dramatic effect on the performance of pre-emergence black-grass herbicides in winter wheat, latest Agrovista trials show.
With bills approaching £100 per hectare (£40/acre) for the pre-emergence spray alone on some farms, growers need to ensure they eke out the best possible performance from their pre-em chemistry.
Agrovista technical manager Mark Hemmant, says in a good year, 80 per cent or more control might be achieved but 60 per cent is the norm and it can be much less in a poor year, especially when seedbeds are dry.
However, poor application technique can also have a huge effect on efficacy, judging by the latest results from trials carried out on a heavily infested black-grass site near Lamport, Northamptonshire.
While a freshly drilled seedbed looks an easy enough target to cover effectively, results suggest otherwise. A few tweaks can make the difference between excellent control and failure, even in relatively dry conditions, he says.
“To get the best results from pre-ems you want good soil coverage. In our trials, control ranged from 10 per cent to 95 per cent plus, simply by changing the application – everything else stagyed the same.”
The trials examined the effect of nozzle choice, water volume, spray pressure, adjuvant choice and boom height on black-grass control. All tests, apart from the last, used a boom height of 50cm (20in).
Air inclusion
Air inclusion nozzles struggled in the trial. Applying herbicides through a set of blue 03 Guardian Air nozzles angled forward and backwards alternately along the boom to comply with the LEARP low-drift three-star rating (1.5 bar, 10kph to deliver 100 litres/ha) produced the worst result of the whole trial, says Mr Hemmant.
“Control was about 10-15 per cent at best. Although these settings are unlikely to be used in practice as no pre-em herbicide yet has a LERAP requirement, we still want to investigate as this may not always be the case.”
Doubling the pressure to 3 bar, more in line with commercial practice, had some effect, increasing the number of droplets and improving soil coverage. Although drift increased due to the higher speed of 14.5kph (9mph) needed to maintain the 100 litres/ha spray volume, control improved to about 60 per cent.
The effect of drift became more apparent when pressure was raised to 4 bar and speed to 16kph (10mph). “The droplet spectrum was too fine and turbulence was also increased, so fewer drops reached the target.”
Adding Remix, a paraffinic oil made up of long-chain molecules designed to reduce spray drift, had a dramatic effect. “It transformed control, boosting it to about 85 per cent,” says Mr Hemmant.
The final air inclusion test used brown 05 nozzles to deliver 200 litres/ha at the three-star rated application of 1.5 bar and 8.5kph (5mph). “Control was much better than the 03s at 100 litres/ha but still not very pretty.” Increasing the pressure had little subsequent effect on efficacy, he adds.
Flat fans
Flat fans gave much better results. Even the basic set-up of red CP 80-04 nozzles at 200 litres/ha (3bar/10kph or 6mph) angled vertically outperformed any of the air inclusion nozzles in the trial, producing about 75 per cent control.
Halving the water volume using a VP 80-03 blue nozzle compromised control by at least 20 percent, despite angling nozzles alternately forward 30 degrees straight down to minimise shadowing of the spray by clods. “We used the same pressure but speed rose to more than 14kph. Going faster with the finer spray inevitable created more drift.”
Adding another line to the sprayer using the small nozzles, pressure and speed transformed the result. The front nozzles were inclined forward 30 degrees and the backline were set vertical.
“This ended up doubling the volume to 200 litres/ha and also produced lots more droplets,” says Mr Hemmant. “In this trial we probably got more than 90 per cent control. And, because of the higher speed, we also increased work rate significantly compared with the red nozzles.
“We then used 300 litres/ha by reducing the speed to about 10kph (6mph). The result was incredible as the extra water volume and large number of droplets optimised seedbed coverage and we saw almost 100 percent control from a pre-em only.”
Key findings
Spray application technique can have a dramatic effect on the performance of pre-emergence black-grass herbicides in winter wheat, latest Agrovista trials show.
With bills approaching £100 per hectare (£40/acre) for the pre-emergence spray alone on some farms, growers need to ensure they eke out the best possible performance from their pre-em chemistry.
Agrovista technical manager Mark Hemmant, says in a good year, 80 per cent or more control might be achieved but 60 per cent is the norm and it can be much less in a poor year, especially when seedbeds are dry.
However, poor application technique can also have a huge effect on efficacy, judging by the latest results from trials carried out on a heavily infested black-grass site near Lamport, Northamptonshire.
While a freshly drilled seedbed looks an easy enough target to cover effectively, results suggest otherwise. A few tweaks can make the difference between excellent control and failure, even in relatively dry conditions, he says.
“To get the best results from pre-ems you want good soil coverage. In our trials, control ranged from 10 per cent to 95 per cent plus, simply by changing the application – everything else stagyed the same.”
The trials examined the effect of nozzle choice, water volume, spray pressure, adjuvant choice and boom height on black-grass control. All tests, apart from the last, used a boom height of 50cm (20in).
Air inclusion
Air inclusion nozzles struggled in the trial. Applying herbicides through a set of blue 03 Guardian Air nozzles angled forward and backwards alternately along the boom to comply with the LEARP low-drift three-star rating (1.5 bar, 10kph to deliver 100 litres/ha) produced the worst result of the whole trial, says Mr Hemmant.
“Control was about 10-15 per cent at best. Although these settings are unlikely to be used in practice as no pre-em herbicide yet has a LERAP requirement, we still want to investigate as this may not always be the case.”
Doubling the pressure to 3 bar, more in line with commercial practice, had some effect, increasing the number of droplets and improving soil coverage. Although drift increased due to the higher speed of 14.5kph (9mph) needed to maintain the 100 litres/ha spray volume, control improved to about 60 per cent.
The effect of drift became more apparent when pressure was raised to 4 bar and speed to 16kph (10mph). “The droplet spectrum was too fine and turbulence was also increased, so fewer drops reached the target.”
Adding Remix, a paraffinic oil made up of long-chain molecules designed to reduce spray drift, had a dramatic effect. “It transformed control, boosting it to about 85 per cent,” says Mr Hemmant.
The final air inclusion test used brown 05 nozzles to deliver 200 litres/ha at the three-star rated application of 1.5 bar and 8.5kph (5mph). “Control was much better than the 03s at 100 litres/ha but still not very pretty.” Increasing the pressure had little subsequent effect on efficacy, he adds.
Flat fans
Flat fans gave much better results. Even the basic set-up of red CP 80-04 nozzles at 200 litres/ha (3bar/10kph or 6mph) angled vertically outperformed any of the air inclusion nozzles in the trial, producing about 75 per cent control.
Halving the water volume using a VP 80-03 blue nozzle compromised control by at least 20 percent, despite angling nozzles alternately forward 30 degrees straight down to minimise shadowing of the spray by clods. “We used the same pressure but speed rose to more than 14kph. Going faster with the finer spray inevitable created more drift.”
Adding another line to the sprayer using the small nozzles, pressure and speed transformed the result. The front nozzles were inclined forward 30 degrees and the backline were set vertical.
“This ended up doubling the volume to 200 litres/ha and also produced lots more droplets,” says Mr Hemmant. “In this trial we probably got more than 90 per cent control. And, because of the higher speed, we also increased work rate significantly compared with the red nozzles.
“We then used 300 litres/ha by reducing the speed to about 10kph (6mph). The result was incredible as the extra water volume and large number of droplets optimised seedbed coverage and we saw almost 100 percent control from a pre-em only.”
Key findings
300 litres/ha better than 200, which, in turn, was better than 100
VP80 found to be better than air inclusion
Twin line found to be better than single
Three-star rated nozzle settings gave poor efficacy