Article taken from the CPM, written by Tom Allen-Stevens
Fungicide application
The last few years have seen new fungicides offering growers new standards in disease control, but the question remains – How do you maximise fungicidal activity in the new chemistry and existing products? This quest has been evaluated in Agrovista’s trials, and in addition to product comparison, application technology has been looked at to increase disease control.
It’s only so far you can rely on fungicides to deliver the disease control you need. Put them on late or when conditions are compromised, and you’re not only in danger of letting pathogens past your defences, you run the risk of encourage them to become resistant to the very chemistry you’re applying.
The trouble is, with the best will in the world, it’s very rate that a product is applied to the crop at exactly the right timing in ideal conditions, points out Agrovista technical manager Mark Hemmant. Growers, especially those with a large area to cover, can rarely wait for the best spray days because timing is so important, even with the latest chemistry, he stresses. Equally, disease programmes for septoria control are moving ever more towards keeping crops protected, increasing the need to be more timely.
Finding practical approaches to maintain efficacy when spray timing and conditions are compromised has been the aim of a series of trials undertaken by the company since 2006. A good understanding of nozzle design and adjuvant use, and how they’re best brought into play, can help protect the chemistry, as well as your crop.
How important is timing?
All fungicides perform best when used in a protectant situation. With septoria, there’s a long latent period – usually 3-4 weeks – during which a plant is infected but will not show symptoms. Rusts cycle more frequently – typically every 7-10 days. Sprays timed at the start of these cycles have the greatest chance of maintaining control of disease.
SDHIs currently offer the best level of curative activity against septoria but azoles are gradually losing their kick-back activity as the pathogen becomes more resistant. Relying more on the SDHIs will increase the likelihood of resistance to this important group of chemistry. So timing sprays to remain in a protectant situation is paramount.
Key spray timings have been identified, with the emergence of leaf three (GS32) and flag leaf (GS39) being the most important. The flag leaf and leaf two are the biggest contributor to yield, and is at its most vulnerable to infection as it emerges. Leaf three overlaps it at this stage, so if the plant is infected at GS32, then the flag leaf could emerge through a disease-ridden canopy.
Agrovista trials have shown timing has a big impact on yield. Where the optimum timing of a triazole-based T2 is allowed to slip just one week, the yield potential of the crop drops by almost 0.5t/ha. With SDHIs, the effect is even more pronounced, and up to 1t/ha can be lost.
How does nozzle choice influence efficacy?
The standard nozzle is the 110° flat-fan (FF) type, used at a water volume of 100 l/ha or 200 l/ha. This produces a range of droplet size, and importantly, the fine spray that’s most effective at coating the leaf and penetrating into the canopy.
The downside of the FF nozzle is that smaller droplets are more prone to drift. However, air-inclusion (AI) nozzles draw in air and mix it with the spray. As a result, larger, air-filled droplets are formed, which are less prone to drift for the same water volume.
Over five years of testing SDHI/triazole fungicides using different nozzle types, FF nozzles were found to be consistently more effective in standard situations, brining an average yield advantage over AI types of 0.29t/ha. They out-performed Guardian Air nozzles by 0.45t/ha, on average.
Where AI nozzles come into their own, however, is in more marginal conditions where using a standard FF nozzle would result in too much drift. Any reduction in application efficacy can be easily outweighed by the increased efficacy from applying the fungicide at the correct timing.
What influence does water volume have?
Spraying at 100 l/ha has performed consistently better than 200 l/ha in the trials, bringing up to 0.5t/ha yield advantage in a high-disease pressure situation. The finer spray helps, but more concentrated droplets probably contributes a greater benefit.
In the field, you’d also benefit from increased work rates, which means more of the cropped area can be covered at the optimum spray timing. You can typically expect the work rate to increase by 33% from halving the water volume. The only situations where efficacy would be comprised would be if there was really bad septoria.
Other downsides of reducing the water volume include increased spray drift and a droplet that dries faster on the leaf, which may reduce the degree of uptake. There may also be compatibility issues with the increased spray concentration.
What effect does angling the nozzle have?
The spray curtain has the effect of moving through the crop as a solid sheet. This creates its own air current, and the negative pressure behind the spray curtain can create eddies that disperse finer spray droplets.
In theory, angling the spray backwards (as with the Amistar nozzle) should reduce the effect, but in Agrovista trials using an AI angled nozzle, this was actually less effective than a nozzle directed straight down as it caused more drift.
The best results were achieved by alternating the nozzle 30° forward and straight down. This probably has the effect of breaking the spray curtain, allowing air to pass through it without creating the currents that disturb the finer droplets.
What effect do adjuvants have?
When using FF nozzles at the correct boom height, adjuvants often add to application efficacy, but add in any factor that would increase drift, and they begin to show a bigger benefit. Similarly, while you get best results from FF nozzles, you can bring the performance of an AI nozzle up to the level of an FF nozzle by using specialist adjuvants.
Trials conducted by Agrovista across Europe in 2013 showed an average yield advantage of around 0.3t/ha from adding Velocity to fungicide treatments. Where a Guardian Air nozzle is used, added Velocity to an SDHI at the T1 timing brought almost 1.5t/ha extra yield, according to UK trials in 2012.
What effect does boom height have?
If the boom height is doubled, all other things being equal, then drift increases by a factor of around 10 with FF nozzles. It’s arguably the biggest application-related cause of poor performance of fungicides, aside from spray timing. But with larger boom widths, there’s a tendency for operators to spray at more than the optimum 0.5m above the crop.
When sprayed at a 1m boom height, trials have show that FF nozzle performance drops off significantly, and ongoing trials are evaluating various drift retardants for use with them.
AI nozzles come into their own when conditions might encourage drift. Their poorer performance compared with FF nozzles can be more than compensated for by adding Velocity.
Fungicide application: top tips
Sponsors message
The Growers Choice Insite trials programme, conducted by Agrovista UK, lies at the heart of their success in providing the most up-to-date and unbiased technical information possible.
This information is then utilised on farm to maximise gross margins in a consistent, cost-effective and responsible manner. This in-depth programme is dedicated to finding practical solutions to crop production problems, whether in the broad-acre arable crops or in the pursuit of high-value fruit and vegetable produce.
With a series of fully replicated major trials sits, managed to the highest standard, it constitutes one of the largest independent trials programmes in the UK. These trials protocols not only study the crop protection inputs, but also the variety, site class, nutritional regime and how different cultivation techniques affect yield and quality. Furthermore, the trials sites are situated across the country to ensure that local climatic conditions – as well as various soil types – are taken into account
Fungicide application
The last few years have seen new fungicides offering growers new standards in disease control, but the question remains – How do you maximise fungicidal activity in the new chemistry and existing products? This quest has been evaluated in Agrovista’s trials, and in addition to product comparison, application technology has been looked at to increase disease control.
It’s only so far you can rely on fungicides to deliver the disease control you need. Put them on late or when conditions are compromised, and you’re not only in danger of letting pathogens past your defences, you run the risk of encourage them to become resistant to the very chemistry you’re applying.
The trouble is, with the best will in the world, it’s very rate that a product is applied to the crop at exactly the right timing in ideal conditions, points out Agrovista technical manager Mark Hemmant. Growers, especially those with a large area to cover, can rarely wait for the best spray days because timing is so important, even with the latest chemistry, he stresses. Equally, disease programmes for septoria control are moving ever more towards keeping crops protected, increasing the need to be more timely.
Finding practical approaches to maintain efficacy when spray timing and conditions are compromised has been the aim of a series of trials undertaken by the company since 2006. A good understanding of nozzle design and adjuvant use, and how they’re best brought into play, can help protect the chemistry, as well as your crop.
How important is timing?
All fungicides perform best when used in a protectant situation. With septoria, there’s a long latent period – usually 3-4 weeks – during which a plant is infected but will not show symptoms. Rusts cycle more frequently – typically every 7-10 days. Sprays timed at the start of these cycles have the greatest chance of maintaining control of disease.
SDHIs currently offer the best level of curative activity against septoria but azoles are gradually losing their kick-back activity as the pathogen becomes more resistant. Relying more on the SDHIs will increase the likelihood of resistance to this important group of chemistry. So timing sprays to remain in a protectant situation is paramount.
Key spray timings have been identified, with the emergence of leaf three (GS32) and flag leaf (GS39) being the most important. The flag leaf and leaf two are the biggest contributor to yield, and is at its most vulnerable to infection as it emerges. Leaf three overlaps it at this stage, so if the plant is infected at GS32, then the flag leaf could emerge through a disease-ridden canopy.
Agrovista trials have shown timing has a big impact on yield. Where the optimum timing of a triazole-based T2 is allowed to slip just one week, the yield potential of the crop drops by almost 0.5t/ha. With SDHIs, the effect is even more pronounced, and up to 1t/ha can be lost.
How does nozzle choice influence efficacy?
The standard nozzle is the 110° flat-fan (FF) type, used at a water volume of 100 l/ha or 200 l/ha. This produces a range of droplet size, and importantly, the fine spray that’s most effective at coating the leaf and penetrating into the canopy.
The downside of the FF nozzle is that smaller droplets are more prone to drift. However, air-inclusion (AI) nozzles draw in air and mix it with the spray. As a result, larger, air-filled droplets are formed, which are less prone to drift for the same water volume.
Over five years of testing SDHI/triazole fungicides using different nozzle types, FF nozzles were found to be consistently more effective in standard situations, brining an average yield advantage over AI types of 0.29t/ha. They out-performed Guardian Air nozzles by 0.45t/ha, on average.
Where AI nozzles come into their own, however, is in more marginal conditions where using a standard FF nozzle would result in too much drift. Any reduction in application efficacy can be easily outweighed by the increased efficacy from applying the fungicide at the correct timing.
What influence does water volume have?
Spraying at 100 l/ha has performed consistently better than 200 l/ha in the trials, bringing up to 0.5t/ha yield advantage in a high-disease pressure situation. The finer spray helps, but more concentrated droplets probably contributes a greater benefit.
In the field, you’d also benefit from increased work rates, which means more of the cropped area can be covered at the optimum spray timing. You can typically expect the work rate to increase by 33% from halving the water volume. The only situations where efficacy would be comprised would be if there was really bad septoria.
Other downsides of reducing the water volume include increased spray drift and a droplet that dries faster on the leaf, which may reduce the degree of uptake. There may also be compatibility issues with the increased spray concentration.
What effect does angling the nozzle have?
The spray curtain has the effect of moving through the crop as a solid sheet. This creates its own air current, and the negative pressure behind the spray curtain can create eddies that disperse finer spray droplets.
In theory, angling the spray backwards (as with the Amistar nozzle) should reduce the effect, but in Agrovista trials using an AI angled nozzle, this was actually less effective than a nozzle directed straight down as it caused more drift.
The best results were achieved by alternating the nozzle 30° forward and straight down. This probably has the effect of breaking the spray curtain, allowing air to pass through it without creating the currents that disturb the finer droplets.
What effect do adjuvants have?
When using FF nozzles at the correct boom height, adjuvants often add to application efficacy, but add in any factor that would increase drift, and they begin to show a bigger benefit. Similarly, while you get best results from FF nozzles, you can bring the performance of an AI nozzle up to the level of an FF nozzle by using specialist adjuvants.
Trials conducted by Agrovista across Europe in 2013 showed an average yield advantage of around 0.3t/ha from adding Velocity to fungicide treatments. Where a Guardian Air nozzle is used, added Velocity to an SDHI at the T1 timing brought almost 1.5t/ha extra yield, according to UK trials in 2012.
What effect does boom height have?
If the boom height is doubled, all other things being equal, then drift increases by a factor of around 10 with FF nozzles. It’s arguably the biggest application-related cause of poor performance of fungicides, aside from spray timing. But with larger boom widths, there’s a tendency for operators to spray at more than the optimum 0.5m above the crop.
When sprayed at a 1m boom height, trials have show that FF nozzle performance drops off significantly, and ongoing trials are evaluating various drift retardants for use with them.
AI nozzles come into their own when conditions might encourage drift. Their poorer performance compared with FF nozzles can be more than compensated for by adding Velocity.
Fungicide application: top tips
Timing is key – use fungicides as protectant products, and avoid relying on SDHIs for curative activity. Lower water volumes increase work rates.
Choose the appropriate nozzle – an FF type will work best in good conditions, but an AI nozzle may be better if work rates become constrained. Best results come when they are angled forwards and down.
Consider use of an adjuvant – these can help, particularly where efficacy is affected by boom height or use of an AI nozzle.
Sponsors message
The Growers Choice Insite trials programme, conducted by Agrovista UK, lies at the heart of their success in providing the most up-to-date and unbiased technical information possible.
This information is then utilised on farm to maximise gross margins in a consistent, cost-effective and responsible manner. This in-depth programme is dedicated to finding practical solutions to crop production problems, whether in the broad-acre arable crops or in the pursuit of high-value fruit and vegetable produce.
With a series of fully replicated major trials sits, managed to the highest standard, it constitutes one of the largest independent trials programmes in the UK. These trials protocols not only study the crop protection inputs, but also the variety, site class, nutritional regime and how different cultivation techniques affect yield and quality. Furthermore, the trials sites are situated across the country to ensure that local climatic conditions – as well as various soil types – are taken into account