As cereal crops progress into the most important part of the growing year, there is great promise across fields of both winter and spring cereals. The wet and windy May weather has followed the relatively mild wet winter and the cold dry spring.
Modern cereal crops have really good genetics and part of what they bring is climate resilience.
While many scientists believe that this resilience needs significant improvement to cope with future climate challenges, farmers can see that it already contributes week on week across the season to add to crop yield and quality.
Differences are evident between crop species in this regard. Wheat and oats generally show more coping ability in wet and cold weather than barley, for example.
Crop resilience to adverse conditions is worth noting because cereals can recover and compensate in a very expected and often dramatic way throughout the crop establishment, tillering and canopy development phases of growth.
Good farmers with well-timed management practices use this genetic resilience to help produce very good crops by mid-season or the full canopy stage.
But after full canopy and the ear emergence stage, the potential for further compensation is practically over and any management errors can have serious consequences.
On a “micro” level, crops can still compensate within spikelets and within neighbouring grains for assimilate during grain fill, but in the overall context any loss of leaf, loss of grain sites, diseased grains, etc will have a very direct negative effect on grain yield.
Losses are unpredictable
The magnitude of this loss is very unpredictable. In a year like 2020, even in Ireland, the losses from disease incidence during grain filling were small and often insignificant.
These were generally modest single-figure percentage losses of between 3% and 8% when comparing treated and untreated plots.
However, there was one geographical exception in 2020, as trial results from parts of Cork showed much bigger differences due the different growing season there.
In a more normal season, with high disease pressure in the key summer months of May and June, this potential loss can be higher in Ireland, with figures of 20% to 40% being realistic levels of grain yield loss.
Yield loss is no mystery
It is easy to calculate where this figure of 20% to 40% yield loss comes from scientifically.
If a winter wheat crop has a 10% flag leaf disease infection at flowering, this can increase to 30% three weeks later and then to 50% by the end of grain fill.
This is a fairly cautious estimate of disease progress in June and July in a poorly protected crop in a disease epidemic scenario. This level of infection will equate to a 30% yield loss to that crop.
One can do a similar sum for spring barley and a scenario where ramularia infection increases from 0% to 40% on the upper leaves and awns during the grain filling period will equate to a 15% to 20% hit on grain yield.
A cool, wet, early summer makes for a great growing scenario for high-yield cereal crops.
Soil is moist, nutrient uptake is excellent, crop structure and crop canopy development are optimised, and yield potential is pushed to its highest level.
The final two stages needed to deliver this are good to very good summer sunshine (now) and decent harvest conditions.
What is also needed is a high level of crop protection, specifically from key fungal diseases.
All the components of high yield potential in a cereal crop (wheat, barley or oats) – density, structure, high grain site numbers, long duration of leaf area and longer grain filling – also increase the risk of a negative disease impact. So good crop protection becomes very important in a high-yield-potential crop.
Late-season – review success to date
Good disease control programmes start in spring with sensible crop nutrition combined with well-timed fungicide applications.
The ear sprays are the final part of the control programme and in many ways they are the most straightforward part. This is because if the previous spray(s) (T1 and possibly T2) have been successful, they will have minimised the disease epidemic risk of key pathogens such as rhyncho in barley and septoria in wheat.
So, the first part of deciding on the strategy for the final spray is to have an accurate review of how well the earlier part of the disease control programme has gone.
Winter wheat and winter/spring oats are good examples of this. If the earlier sprays have gone on at good timings and provided good control efficacy, then it makes the ear spray a lot more straightforward.
Target diseases
In wheat, the ear spray will target two diseases – Fusarium ear blight and septoria. Efficacy on ear blight/Fusarium is a function of good timing – ideally GS65 but +/- five to seven days.
Also key here is a robust dose of triazole fungicides with a combination of prothioconazole and either metconazole or tebuconazole to give good to very good efficacy, which is likely to peak at 65% to 70% control.
This type of treatment will also give moderate septoria efficacy of around 50% to 60%, which should be adequate if the earlier treatments have worked well. This is likely to be the case in 2021 if high levels of Inatreq and Revysol are used with partners at T2.
In oats, it’s steady as you go for product choice. Recent product losses are biting here, with high-profile products no longer in the market.
The outstanding efficacy of Elatus Era on mildew and rust makes it a go-to option in many situations and it has a rate flexibility which makes it a good option in many crop scenarios.
The other key aspect in oats is crop health and grain/kernel colour and robust rates will deliver better outcomes in this regard.
Challenging times for barley
Since ramularia leaf blotch was identified as a problem disease in barley production in western Europe 25 years ago, it has been an unpredictable pathogen.
Initially, it was speculated as to whether such a non-aggressive and benign pathogen could be considered “serious”. However, its devastating effects on the yield and quality of the malting crop in the Cooper Blotch years in the late 1990s quickly changed its rating.
The overnight breakthrough solution was the use of chlorothalonil (CTL) at T2. This chemical was rarely used on barley previously but for 20-odd years it provided a simple reliable and very effective control option, with 80% to 90% control expected form a single spray at T2.
None of the options post CTL are going to be as effective or as simple in providing a high level of control.
The Teagasc article in the Irish Farmers Journal Crop Protection supplement in April gives an excellent appraisal of the overall approach to ramularia control and highlights the need to take a more integrated control approach into the future to minimise the risk of yield loss.
A key element of this control strategy is the optimisation of the effectiveness of the final fungicide spray.
The resistance issue is everywhere. Many of the fungicide options for ramularia control – the strobilurins, SDHIs and older azoles – are all compromised in their efficacy. Variable control levels can be expected in 2021, ranging from low to moderate and typically 30% to 60%.
The two other actives of most interest are the new azole Revysol and the contact product folpet. Both have performed well when used alone and in combination in trials in Ireland in recent years.
However, a realistic efficacy for ramularia control post-CTL is 70% to 75% and this can be achieved in a cost-effective way by using combinations of the aforementioned actives but a systemic plus contact active must be used.
Focus on spray timing
The most important determinant of fungicide performance on ramularia is timing.
All the fungicide options mentioned previously need to be used preventatively, so a timing window of GS39-45 is critical for effective control.
There is also an interest in a T1.5 / T2 split-dose approach for ramularia control, which is probably more applicable to a winter barley scenario and this is currently the focus of research trials.
Where application timing is poor/delayed and applied curatively, the control efficacy would be easily halved from any combination of the fungicides outlined previously.
So, the single most important part of successful ramularia control is timing and everything else in the approach works from this.
Ensuring good foliar disease control is critical for safeguarding good grain fill in all cereals.All fungicide treatments matter, but the success of the final treatment will be influenced by the efficacy of the previous sprays.The success of ramularia in overcoming fungicide families necessitates the need for a more integrated approach to its control.Ramularia control depends on fungicides acting preventatively and so the products must be applied well ahead of the likely development of the disease.Control of ear blight is best targeted by a mid-flowering spray using robust application rates.
As cereal crops progress into the most important part of the growing year, there is great promise across fields of both winter and spring cereals. The wet and windy May weather has followed the relatively mild wet winter and the cold dry spring.
Modern cereal crops have really good genetics and part of what they bring is climate resilience.
While many scientists believe that this resilience needs significant improvement to cope with future climate challenges, farmers can see that it already contributes week on week across the season to add to crop yield and quality.
Differences are evident between crop species in this regard. Wheat and oats generally show more coping ability in wet and cold weather than barley, for example.
Crop resilience to adverse conditions is worth noting because cereals can recover and compensate in a very expected and often dramatic way throughout the crop establishment, tillering and canopy development phases of growth.
Good farmers with well-timed management practices use this genetic resilience to help produce very good crops by mid-season or the full canopy stage.
But after full canopy and the ear emergence stage, the potential for further compensation is practically over and any management errors can have serious consequences.
On a “micro” level, crops can still compensate within spikelets and within neighbouring grains for assimilate during grain fill, but in the overall context any loss of leaf, loss of grain sites, diseased grains, etc will have a very direct negative effect on grain yield.
Losses are unpredictable
The magnitude of this loss is very unpredictable. In a year like 2020, even in Ireland, the losses from disease incidence during grain filling were small and often insignificant.
These were generally modest single-figure percentage losses of between 3% and 8% when comparing treated and untreated plots.
However, there was one geographical exception in 2020, as trial results from parts of Cork showed much bigger differences due the different growing season there.
In a more normal season, with high disease pressure in the key summer months of May and June, this potential loss can be higher in Ireland, with figures of 20% to 40% being realistic levels of grain yield loss.
Yield loss is no mystery
It is easy to calculate where this figure of 20% to 40% yield loss comes from scientifically.
If a winter wheat crop has a 10% flag leaf disease infection at flowering, this can increase to 30% three weeks later and then to 50% by the end of grain fill.
This is a fairly cautious estimate of disease progress in June and July in a poorly protected crop in a disease epidemic scenario. This level of infection will equate to a 30% yield loss to that crop.
One can do a similar sum for spring barley and a scenario where ramularia infection increases from 0% to 40% on the upper leaves and awns during the grain filling period will equate to a 15% to 20% hit on grain yield.
A cool, wet, early summer makes for a great growing scenario for high-yield cereal crops.
Soil is moist, nutrient uptake is excellent, crop structure and crop canopy development are optimised, and yield potential is pushed to its highest level.
The final two stages needed to deliver this are good to very good summer sunshine (now) and decent harvest conditions.
What is also needed is a high level of crop protection, specifically from key fungal diseases.
All the components of high yield potential in a cereal crop (wheat, barley or oats) – density, structure, high grain site numbers, long duration of leaf area and longer grain filling – also increase the risk of a negative disease impact. So good crop protection becomes very important in a high-yield-potential crop.
Late-season – review success to date
Good disease control programmes start in spring with sensible crop nutrition combined with well-timed fungicide applications.
The ear sprays are the final part of the control programme and in many ways they are the most straightforward part. This is because if the previous spray(s) (T1 and possibly T2) have been successful, they will have minimised the disease epidemic risk of key pathogens such as rhyncho in barley and septoria in wheat.
So, the first part of deciding on the strategy for the final spray is to have an accurate review of how well the earlier part of the disease control programme has gone.
Winter wheat and winter/spring oats are good examples of this. If the earlier sprays have gone on at good timings and provided good control efficacy, then it makes the ear spray a lot more straightforward.
Target diseases
In wheat, the ear spray will target two diseases – Fusarium ear blight and septoria. Efficacy on ear blight/Fusarium is a function of good timing – ideally GS65 but +/- five to seven days.
Also key here is a robust dose of triazole fungicides with a combination of prothioconazole and either metconazole or tebuconazole to give good to very good efficacy, which is likely to peak at 65% to 70% control.
This type of treatment will also give moderate septoria efficacy of around 50% to 60%, which should be adequate if the earlier treatments have worked well. This is likely to be the case in 2021 if high levels of Inatreq and Revysol are used with partners at T2.
In oats, it’s steady as you go for product choice. Recent product losses are biting here, with high-profile products no longer in the market.
The outstanding efficacy of Elatus Era on mildew and rust makes it a go-to option in many situations and it has a rate flexibility which makes it a good option in many crop scenarios.
The other key aspect in oats is crop health and grain/kernel colour and robust rates will deliver better outcomes in this regard.
Challenging times for barley
Since ramularia leaf blotch was identified as a problem disease in barley production in western Europe 25 years ago, it has been an unpredictable pathogen.
Initially, it was speculated as to whether such a non-aggressive and benign pathogen could be considered “serious”. However, its devastating effects on the yield and quality of the malting crop in the Cooper Blotch years in the late 1990s quickly changed its rating.
The overnight breakthrough solution was the use of chlorothalonil (CTL) at T2. This chemical was rarely used on barley previously but for 20-odd years it provided a simple reliable and very effective control option, with 80% to 90% control expected form a single spray at T2.
None of the options post CTL are going to be as effective or as simple in providing a high level of control.
The Teagasc article in the Irish Farmers Journal Crop Protection supplement in April gives an excellent appraisal of the overall approach to ramularia control and highlights the need to take a more integrated control approach into the future to minimise the risk of yield loss.
A key element of this control strategy is the optimisation of the effectiveness of the final fungicide spray.
The resistance issue is everywhere. Many of the fungicide options for ramularia control – the strobilurins, SDHIs and older azoles – are all compromised in their efficacy. Variable control levels can be expected in 2021, ranging from low to moderate and typically 30% to 60%.
The two other actives of most interest are the new azole Revysol and the contact product folpet. Both have performed well when used alone and in combination in trials in Ireland in recent years.
However, a realistic efficacy for ramularia control post-CTL is 70% to 75% and this can be achieved in a cost-effective way by using combinations of the aforementioned actives but a systemic plus contact active must be used.
Focus on spray timing
The most important determinant of fungicide performance on ramularia is timing.
All the fungicide options mentioned previously need to be used preventatively, so a timing window of GS39-45 is critical for effective control.
There is also an interest in a T1.5 / T2 split-dose approach for ramularia control, which is probably more applicable to a winter barley scenario and this is currently the focus of research trials.
Where application timing is poor/delayed and applied curatively, the control efficacy would be easily halved from any combination of the fungicides outlined previously.
So, the single most important part of successful ramularia control is timing and everything else in the approach works from this.
Ensuring good foliar disease control is critical for safeguarding good grain fill in all cereals.All fungicide treatments matter, but the success of the final treatment will be influenced by the efficacy of the previous sprays.The success of ramularia in overcoming fungicide families necessitates the need for a more integrated approach to its control.Ramularia control depends on fungicides acting preventatively and so the products must be applied well ahead of the likely development of the disease.Control of ear blight is best targeted by a mid-flowering spray using robust application rates. 
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