The heading above possibly best describes the summary of last week’s Teagasc’s septoria conference. Basically, we are on the edge of resistance development to the SHDI fungicides as mutants that will not be controlled by SDHIs are already present. And the more intensively we use fungicides to control this disease, the more intensively we select for these resistant types. Ultimately, this would mean product failure or uneconomical treatment.
Septoria as an entity might best be likened to the human population. It is composed of many types with many characteristics. Imagine if a fungicide did the job of removing all people above a certain height, or with certain eye or hair colour or above a certain weight within the population – well there would always be some left and these would then be more difficult to kill with that active. If we kept using that active then the remaining population would no longer be affected by that active, otherwise known as resistant.
In an intensive day of presentation on a single disease, three things became quite clear:
Resistance marches on and it is most heavily influenced by the intensive use of fungicides.Our ability to stay on top of some diseases using fungicides is becoming increasingly limited and future new actives may not change this situation for the longer term.All players in the industry are telling the same story and with the same emphasis.A universal problem
We, in Ireland, are not unique with these problems and challenges. It was apparent from the different international presentations that all areas that use fungicides intensively have challenges from resistance or reduced insensitivity. Some regions of the world have lesser problems because they are not challenged by wet season fungal diseases while others, especially in northern Europe, have big challenges.
The problem even varies within regions. Differing historic approaches to disease control have resulted in areas using specific fungicide classes or modes of action more frequently than others and this drives the resultant population. This is even true to some degree within Ireland where metconazole is potentially more useful in the northern half of the country but this too will change with its continued use.
For these reasons, different isolates or mutants tend to be more prominent in different countries or parts of countries. But they all mean the same thing – reduced control capacity. This means less rate flexibility now than previously and most modes of action have less curative capacity. The result means less ability to control septoria, especially from the long serving azole group.
A fungicide breaker
The challenge for septoria control is very stark. Neil Paveley from ADAS reported that current research on resistance drivers showed the use of high rates of active, more sprays giving more frequent exposure to the same mode of action and the use of more applications of split doses are all strong drivers or selectors for resistance in a population. We, in Ireland, fall foul on all of these pointers but then what do we do?
Septoria is a yield-robbing disease and it must be controlled. There is no doubt but that if we stopped growing wheat or stopped spraying fungicides we would stop selecting for resistance, and perhaps that day will come. But in the meantime we must do all we can, at grower, adviser, research and industry level, to slow the current selection trends. Paveley concluded that septoria breaks fungicides because we use so much fungicides.
New and useful tools
One of the conference sessions dealt with areas that hope to offer potential for future control. These are new chemical modes of action and offer better and more durable variety resistance. There was certainly hope on both fronts. We were told of a number of new actives coming through the pipeline that appear to be starting with a clean sheet with regard to resistance.
That is certainly good news, but unless we get actives with a number of different modes of action we are still facing the same end game. Some of these actives are already overdue and that is indicative of the increasingly restrictive registration process in the EU. Recent changes in the registration process will continue to give increased challenges, possibly to the point of being unattractive to the multinational chemical developers.
For the moment, we can look forward to a few new actives coming through the registration process. But the continual loss of current actives is a contributory factor to the expansion of resistance. And a conclusion to the endocrine disruptor issue may well herald the loss of many of the azole actives, plus others.
Presentations by the different chemical companies sounded similar messages. There was general agreement that the future of septoria control will not rely on a bottle but the hope is that the bottles can still help with control. All the chemical companies reinforced the importance of integrated pest management (IPM) and doing as many other cultural practices as make sense to help protect the chemical actives.
John Mulhare of Terrachem/DuPont talked about the potential benefits of induced host defence mechanism and the fact that Talius helps other actives like azoles add a little to the control of septoria. This may not have been of tangible benefit when fungicides were very active but the situation is different now.
Barry McKeown from BASF told us about Revysol, a new type of triazole which seems to be coming with a clean sheet with regard to existing known azole mutations. But it will need protection over time if it is to have a useful lifespan.
Andreas Mehl of Bayer CropScience told us about the incomplete cross resistance that exists in triazoles and how we must attempt to capitalise on these differences for more effective disease control and improved protection of the remaining azole sub-groups. He also indicated incomplete cross resistance for some SDHI actives but it seems that this may not apply to all our known field mutants.
John Fraser of Dow CropScience told us about hopes to launch Inatreq in the near future. This is a completely new mode of action and so is a potential mixing partner for current and other new actives in the market.
Jason Tatnell of Syngenta told us about the new SDHI active called Adepidyn. This is already on sale in parts of the world and offers good control potential on leafspots, powdery mildew and ear blights. He also spoke about the potential importance of variety for septoria control in the future.
The final session of the day looked at husbandry aspects which farmers can consider to help contain the disease and help fungicide longevity by helping to decrease selection pressure. The potential for genetic resistance got a lot of attention. We have very few varieties with high resistance levels and it is still generally felt that septoria resistance comes with a yield penalty, or what is known as yield drag.
Varieties play an important role in disease development. Higher genetic resistance levels help to slow disease development and generally affect the level of septoria in both treated and untreated crops. This gets increasingly important as fungicide efficacy decreases.
The challenge for breeders is to build robust multigene resistance to septoria that will be both effective and durable in the field over time. Having strong genetic resistance can help to reduce fungicide rates and the number of sprays, both of which help reduce selection pressure over time.
The general feeling is that breeders have become more successful at breeding for resistance and growers are advised to maximise what we have now, rather than waiting for control failures.
The general message from the meeting is that better genetic resistance means less disease in the field at any point in time. But this still does not necessary mean lower fungicide rates or fewer fungicide applications. When resistances levels become available which provide the option to reduce fungicide input, the resistance rating for septoria will become one of the primary characteristics to be considered in variety choice. Hopefully that day is not too far away but we should not ignore what we have today either.
Husbandry guidance
Variety choice is the number one husbandry consideration – what you sow is what you must grow. The only other tangible effect of husbandry is the sowing date. Fertility, nitrogen, seed rate, growth regulation, etc, can make small differences but they are not consistent enough to be really useful tools to reduce disease pressure. Obviously, fungicides are in the husbandry too and they can still make a huge contribution to control. But how we use them should affect their longevity.
Sowing date is a double-edged sword. There is little doubt that later planting (into November) will decrease septoria infection levels and this may (or may not) be of benefit come spring time. In first wheats in rotational fields, much of the autumn infection occurs as a result of airborne spores blowing in.
There are more of these spores when temperatures are higher and much fewer when temperatures drop. Rainfall probably has some effect here also.
The problem with delaying drilling is that you can run into unfavourable weather. Wet can prevent drilling, damage drilled crops or drive crow attack during establishment. These are among the main reasons why drilling dates have been pulled forward but early drilling leads to earlier infection and more septoria cycles in the autumn and winter. Early drilling is also adding increased grassweed problems.
Where possible, drilling dates should be pulled back into October.
Any September drilling should use more resistant varieties and still only be sown in late September. But the calendar should not be the guide.
Early and late refer to location and geography more so than calendar. What might be early in Donegal is very different to early in south Cork.
Fungicides will hopefully remain the important control mechanism.
But the guidelines on chemicals need to be followed. Use straight triazoles and alternate between the sub-groups (prothioconazole/epoxiconazole and tebuconazole/metconazole).
Always use mixtures of modes of action rather than mixtures within a mode of action and have a multisite in every spray. Not having a mode of action in the tank reduces selection pressure for resistance against that family.
Lower product rates can be advantageous but additional lower rates (splits) drive resistance.
Further information from this conference will be carried in our Crop Protection supplement to be published in mid-April.
The challenge of resistance in septoria to the SDHI fungicides cannot be underestimated.Use of any fungicide mode of action helps to select for resistance or reduced sensitivity.There are new modes of action in the registration pipeline.Breeders are increasing efforts to create higher levels of varietal resistance.Farmers need to alter husbandry as much as possible to help decrease autumn infection pressure.
The heading above possibly best describes the summary of last week’s Teagasc’s septoria conference. Basically, we are on the edge of resistance development to the SHDI fungicides as mutants that will not be controlled by SDHIs are already present. And the more intensively we use fungicides to control this disease, the more intensively we select for these resistant types. Ultimately, this would mean product failure or uneconomical treatment.
Septoria as an entity might best be likened to the human population. It is composed of many types with many characteristics. Imagine if a fungicide did the job of removing all people above a certain height, or with certain eye or hair colour or above a certain weight within the population – well there would always be some left and these would then be more difficult to kill with that active. If we kept using that active then the remaining population would no longer be affected by that active, otherwise known as resistant.
In an intensive day of presentation on a single disease, three things became quite clear:
Resistance marches on and it is most heavily influenced by the intensive use of fungicides.Our ability to stay on top of some diseases using fungicides is becoming increasingly limited and future new actives may not change this situation for the longer term.All players in the industry are telling the same story and with the same emphasis.A universal problem
We, in Ireland, are not unique with these problems and challenges. It was apparent from the different international presentations that all areas that use fungicides intensively have challenges from resistance or reduced insensitivity. Some regions of the world have lesser problems because they are not challenged by wet season fungal diseases while others, especially in northern Europe, have big challenges.
The problem even varies within regions. Differing historic approaches to disease control have resulted in areas using specific fungicide classes or modes of action more frequently than others and this drives the resultant population. This is even true to some degree within Ireland where metconazole is potentially more useful in the northern half of the country but this too will change with its continued use.
For these reasons, different isolates or mutants tend to be more prominent in different countries or parts of countries. But they all mean the same thing – reduced control capacity. This means less rate flexibility now than previously and most modes of action have less curative capacity. The result means less ability to control septoria, especially from the long serving azole group.
A fungicide breaker
The challenge for septoria control is very stark. Neil Paveley from ADAS reported that current research on resistance drivers showed the use of high rates of active, more sprays giving more frequent exposure to the same mode of action and the use of more applications of split doses are all strong drivers or selectors for resistance in a population. We, in Ireland, fall foul on all of these pointers but then what do we do?
Septoria is a yield-robbing disease and it must be controlled. There is no doubt but that if we stopped growing wheat or stopped spraying fungicides we would stop selecting for resistance, and perhaps that day will come. But in the meantime we must do all we can, at grower, adviser, research and industry level, to slow the current selection trends. Paveley concluded that septoria breaks fungicides because we use so much fungicides.
New and useful tools
One of the conference sessions dealt with areas that hope to offer potential for future control. These are new chemical modes of action and offer better and more durable variety resistance. There was certainly hope on both fronts. We were told of a number of new actives coming through the pipeline that appear to be starting with a clean sheet with regard to resistance.
That is certainly good news, but unless we get actives with a number of different modes of action we are still facing the same end game. Some of these actives are already overdue and that is indicative of the increasingly restrictive registration process in the EU. Recent changes in the registration process will continue to give increased challenges, possibly to the point of being unattractive to the multinational chemical developers.
For the moment, we can look forward to a few new actives coming through the registration process. But the continual loss of current actives is a contributory factor to the expansion of resistance. And a conclusion to the endocrine disruptor issue may well herald the loss of many of the azole actives, plus others.
Presentations by the different chemical companies sounded similar messages. There was general agreement that the future of septoria control will not rely on a bottle but the hope is that the bottles can still help with control. All the chemical companies reinforced the importance of integrated pest management (IPM) and doing as many other cultural practices as make sense to help protect the chemical actives.
John Mulhare of Terrachem/DuPont talked about the potential benefits of induced host defence mechanism and the fact that Talius helps other actives like azoles add a little to the control of septoria. This may not have been of tangible benefit when fungicides were very active but the situation is different now.
Barry McKeown from BASF told us about Revysol, a new type of triazole which seems to be coming with a clean sheet with regard to existing known azole mutations. But it will need protection over time if it is to have a useful lifespan.
Andreas Mehl of Bayer CropScience told us about the incomplete cross resistance that exists in triazoles and how we must attempt to capitalise on these differences for more effective disease control and improved protection of the remaining azole sub-groups. He also indicated incomplete cross resistance for some SDHI actives but it seems that this may not apply to all our known field mutants.
John Fraser of Dow CropScience told us about hopes to launch Inatreq in the near future. This is a completely new mode of action and so is a potential mixing partner for current and other new actives in the market.
Jason Tatnell of Syngenta told us about the new SDHI active called Adepidyn. This is already on sale in parts of the world and offers good control potential on leafspots, powdery mildew and ear blights. He also spoke about the potential importance of variety for septoria control in the future.
The final session of the day looked at husbandry aspects which farmers can consider to help contain the disease and help fungicide longevity by helping to decrease selection pressure. The potential for genetic resistance got a lot of attention. We have very few varieties with high resistance levels and it is still generally felt that septoria resistance comes with a yield penalty, or what is known as yield drag.
Varieties play an important role in disease development. Higher genetic resistance levels help to slow disease development and generally affect the level of septoria in both treated and untreated crops. This gets increasingly important as fungicide efficacy decreases.
The challenge for breeders is to build robust multigene resistance to septoria that will be both effective and durable in the field over time. Having strong genetic resistance can help to reduce fungicide rates and the number of sprays, both of which help reduce selection pressure over time.
The general feeling is that breeders have become more successful at breeding for resistance and growers are advised to maximise what we have now, rather than waiting for control failures.
The general message from the meeting is that better genetic resistance means less disease in the field at any point in time. But this still does not necessary mean lower fungicide rates or fewer fungicide applications. When resistances levels become available which provide the option to reduce fungicide input, the resistance rating for septoria will become one of the primary characteristics to be considered in variety choice. Hopefully that day is not too far away but we should not ignore what we have today either.
Husbandry guidance
Variety choice is the number one husbandry consideration – what you sow is what you must grow. The only other tangible effect of husbandry is the sowing date. Fertility, nitrogen, seed rate, growth regulation, etc, can make small differences but they are not consistent enough to be really useful tools to reduce disease pressure. Obviously, fungicides are in the husbandry too and they can still make a huge contribution to control. But how we use them should affect their longevity.
Sowing date is a double-edged sword. There is little doubt that later planting (into November) will decrease septoria infection levels and this may (or may not) be of benefit come spring time. In first wheats in rotational fields, much of the autumn infection occurs as a result of airborne spores blowing in.
There are more of these spores when temperatures are higher and much fewer when temperatures drop. Rainfall probably has some effect here also.
The problem with delaying drilling is that you can run into unfavourable weather. Wet can prevent drilling, damage drilled crops or drive crow attack during establishment. These are among the main reasons why drilling dates have been pulled forward but early drilling leads to earlier infection and more septoria cycles in the autumn and winter. Early drilling is also adding increased grassweed problems.
Where possible, drilling dates should be pulled back into October.
Any September drilling should use more resistant varieties and still only be sown in late September. But the calendar should not be the guide.
Early and late refer to location and geography more so than calendar. What might be early in Donegal is very different to early in south Cork.
Fungicides will hopefully remain the important control mechanism.
But the guidelines on chemicals need to be followed. Use straight triazoles and alternate between the sub-groups (prothioconazole/epoxiconazole and tebuconazole/metconazole).
Always use mixtures of modes of action rather than mixtures within a mode of action and have a multisite in every spray. Not having a mode of action in the tank reduces selection pressure for resistance against that family.
Lower product rates can be advantageous but additional lower rates (splits) drive resistance.
Further information from this conference will be carried in our Crop Protection supplement to be published in mid-April.
The challenge of resistance in septoria to the SDHI fungicides cannot be underestimated.Use of any fungicide mode of action helps to select for resistance or reduced sensitivity.There are new modes of action in the registration pipeline.Breeders are increasing efforts to create higher levels of varietal resistance.Farmers need to alter husbandry as much as possible to help decrease autumn infection pressure. 
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