Article taken from the Agronomist & Arable Farmer
Pre-emergence herbicides play an increasingly vital role on many farms, to take the pressure off or even replace post-emergence chemistry that is struggling to cope with rising black-grass resistance.
With bills approaching £100/ha on some farms for this application alone, growers need to eke out the best possible performance from their pre-em chemistry.
In a good year80% or more control might be achieved, but more often 60% is the norm and much less in a poor year, especially when seed-beds are dry. However, poor application technique can also have a huge effect on efficacy, judging by the latest infested black-grass site near Lamport in Northamptonshire.
While a freshly drilled seed-bed 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.
Obtaining the best results from pre-ems requires good soil coverage. In the trials conducted by Agrovista, control ranged from 10% to 95+% simply by changing the application – everything else stayed the same.
The trials examined the effect of nozzle choice, water volume, spray pressure, adjuvant choice and boom height on black-grass control. All apart from the last used a boom height of 50cm.
Air-inclusion Nozzles
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 their LERAP low-drift three-star rating (1.5 bar, 10kph to deliver 100 litres/ha) produced the worst result of the whole trial.
Control was around 10-15% at best. Although these settings are unlikely to be used in practice as no pre-em herbicide yet has a LERAP requirement, Agrovista wanted to look more deeply at this, as that 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 needed to maintain the 100 litres/ha spray volume, control improved to about 60%.
The effect of drift became more apparent when pressure was raised to 4 bar and the speed raised to 16kph. At these settings, the droplet spectrum was too fine and turbulence increased, so fewer drops reached the target.
Adding Remix, a parafinnic oil made up of long-chain molecules designed to reduce spray drift, had a dramatic effect. It transformed control, boosting it to about 85%. Remix improves the spray pattern, giving a more even distribution of herbicide onto the soil. Its long-chain molecules also help to bind the herbicide active to clay and organic matter, keeping herbicide in the surface layer for longer.
The final air inclusion test used brown 05 nozzles to deliver 200 litres/ha at the three-star rated application (1.5 bar, 8.5kph). Control was much better than the 03s at 100 litres/ha but still not very efficient. Increasing the pressure had little subsequent effect on efficacy.
Flat Fans
Flat fans gave much better results. Even the basic set-up of red CP 80-04 nozzles at 200 litres/ha (3 bar/10kph) angled vertically out-performed any of the air inclusion nozzles in the trial, producing around 75% of control.
Halving the water volume using a VP 80-03 blue nozzle compromised control by at least 20%, despite angling nozzles alternatively forward 30 degrees and straight down to minimise shadowing of the spray by clods. The trial used the same pressure, but speed rose to over 14kph. Going faster with the finer spray inevitable created more drift.
Adding another line to the sprayer using the same nozzle, pressure and speed transformed the result. Front nozzles were inclined forward 30 degrees and the back line set vertical.
The result is a doubling of the volume to 200 litres/ha and also means that more droplets are produced. In these trial conditions control was estimated at over 90%. And, because of the higher speed, work rate was also increased significantly compared with the red nozzles.
The next phase of the trial applied 300 litres/ha by reducing the speed to around 10kph. This result was incredible – the combination of extra water volume and the large number of droplets optimised seed-bed coverage, and achieved almost 100% control from a pre-em only.
Compare that with the control achieved with the air inclusion nozzles. The only difference is the application – showing that you don’t need to spend much to see dramatic improvements.
Getting down to details
Boom Height
Boom height can have a critical effect on herbicide performance, especially when used without an effective adjuvant to help reduce drift.
The trials were sprayed with Liberator at 0.6 litres/ha, plus or minus adjuvant, using a single line of vertical CP 80-03 nozzles applying 150 litres/ha (3 bar/10kph).
Liberator alone applied 1m above the soil gave very poor control (20%). The herbicide performance was hugely improved at the correct boom height of 50cm, entirely due to reduce drift.
The effect was less clear where a good adjuvant was used. Remix stood out at the 1m boom height, boosting control to 90%. It also gave a significant benefit at 50cm. Two other commercial adjuvants had little effect in this trial at either height.
Some modern sprayer booms may not get as low as 50cm. It that’s the case, a recommended solution is to use 80-degree flat fans, twin lines and add Remix to ensure the best result.
Trials
Key Findings
Pre-emergence herbicides play an increasingly vital role on many farms, to take the pressure off or even replace post-emergence chemistry that is struggling to cope with rising black-grass resistance.
With bills approaching £100/ha on some farms for this application alone, growers need to eke out the best possible performance from their pre-em chemistry.
In a good year80% or more control might be achieved, but more often 60% is the norm and much less in a poor year, especially when seed-beds are dry. However, poor application technique can also have a huge effect on efficacy, judging by the latest infested black-grass site near Lamport in Northamptonshire.
While a freshly drilled seed-bed 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.
Obtaining the best results from pre-ems requires good soil coverage. In the trials conducted by Agrovista, control ranged from 10% to 95+% simply by changing the application – everything else stayed the same.
The trials examined the effect of nozzle choice, water volume, spray pressure, adjuvant choice and boom height on black-grass control. All apart from the last used a boom height of 50cm.
Air-inclusion Nozzles
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 their LERAP low-drift three-star rating (1.5 bar, 10kph to deliver 100 litres/ha) produced the worst result of the whole trial.
Control was around 10-15% at best. Although these settings are unlikely to be used in practice as no pre-em herbicide yet has a LERAP requirement, Agrovista wanted to look more deeply at this, as that 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 needed to maintain the 100 litres/ha spray volume, control improved to about 60%.
The effect of drift became more apparent when pressure was raised to 4 bar and the speed raised to 16kph. At these settings, the droplet spectrum was too fine and turbulence increased, so fewer drops reached the target.
Adding Remix, a parafinnic oil made up of long-chain molecules designed to reduce spray drift, had a dramatic effect. It transformed control, boosting it to about 85%. Remix improves the spray pattern, giving a more even distribution of herbicide onto the soil. Its long-chain molecules also help to bind the herbicide active to clay and organic matter, keeping herbicide in the surface layer for longer.
The final air inclusion test used brown 05 nozzles to deliver 200 litres/ha at the three-star rated application (1.5 bar, 8.5kph). Control was much better than the 03s at 100 litres/ha but still not very efficient. Increasing the pressure had little subsequent effect on efficacy.
Flat Fans
Flat fans gave much better results. Even the basic set-up of red CP 80-04 nozzles at 200 litres/ha (3 bar/10kph) angled vertically out-performed any of the air inclusion nozzles in the trial, producing around 75% of control.
Halving the water volume using a VP 80-03 blue nozzle compromised control by at least 20%, despite angling nozzles alternatively forward 30 degrees and straight down to minimise shadowing of the spray by clods. The trial used the same pressure, but speed rose to over 14kph. Going faster with the finer spray inevitable created more drift.
Adding another line to the sprayer using the same nozzle, pressure and speed transformed the result. Front nozzles were inclined forward 30 degrees and the back line set vertical.
The result is a doubling of the volume to 200 litres/ha and also means that more droplets are produced. In these trial conditions control was estimated at over 90%. And, because of the higher speed, work rate was also increased significantly compared with the red nozzles.
The next phase of the trial applied 300 litres/ha by reducing the speed to around 10kph. This result was incredible – the combination of extra water volume and the large number of droplets optimised seed-bed coverage, and achieved almost 100% control from a pre-em only.
Compare that with the control achieved with the air inclusion nozzles. The only difference is the application – showing that you don’t need to spend much to see dramatic improvements.
Getting down to details
Boom Height
Boom height can have a critical effect on herbicide performance, especially when used without an effective adjuvant to help reduce drift.
The trials were sprayed with Liberator at 0.6 litres/ha, plus or minus adjuvant, using a single line of vertical CP 80-03 nozzles applying 150 litres/ha (3 bar/10kph).
Liberator alone applied 1m above the soil gave very poor control (20%). The herbicide performance was hugely improved at the correct boom height of 50cm, entirely due to reduce drift.
The effect was less clear where a good adjuvant was used. Remix stood out at the 1m boom height, boosting control to 90%. It also gave a significant benefit at 50cm. Two other commercial adjuvants had little effect in this trial at either height.
Some modern sprayer booms may not get as low as 50cm. It that’s the case, a recommended solution is to use 80-degree flat fans, twin lines and add Remix to ensure the best result.
Trials
Background black-grass population – 400 heads/m²
Crop – Solstice winter wheat
Sowing date – 28th September
Seedbed – firm, small or medium clods
Chemistry – 240g of flufenacet, 60g DFF and 600g of pendimethalin/ha
Applied 2nd October onto a damp seedbed
Rain
No post-emergence treatments applied
Key Findings
300 litres/ha better than 200 better than 100
VP80 better than air inclusion
Twin line better than single
3* rated nozzles settings = poor efficacy