Grain growers will now be very aware of the risks to the ongoing availability of chlorothalonil (CTL). Best known as Bravo and available as many different brand names, chlorothalonil has been key to successful disease control in wheat and barley in this country for the past few decades. A Teagasc report estimates that net margins could be hit by more than 50% if it is removed.
The active was up for its routine re-registration in October of this year. Changes to its use seemed inevitable. A rate reduction was anticipated, coupled with the likelihood that the maximum dose rate would apply to the active rather than any individual product. But as we got into 2018, the possibility of non-registration seemed more likely.
Case to answer
The registration process indicated that CTL had a case to answer on a number of fronts. Current registration criteria are now based on potential hazards, rather than the risk management of past registrations.
The main concerns would appear to be its alleged carcinogenicity (capacity to produce cancer) and a suggested risk to ground water.
It may be possible to challenge the risk to ground water, in that there has not been talk of such problems occurring in practice, in spite of its extensive use for decades.
But its label has long carried the alleged limited carcinogen rating and this is now a major issue.
We understand that CTL is once again being evaluated by competent European authorities and that this examination is currently causing the delay in the decision, which may now be delayed possibly until December.
It seems inevitable that the results of this test will seal the fate of CTL one way or the other. When we demand that science be the arbitrator of decisions relating to chemicals, we will have little choice but to accept the decision of science in this outcome.
The greater problem has to be the failure of the registration system to take into account the importance of this active for farmers in this part of the world and the failure to have a satisfactory replacement in place in the event of a ban.
Teagasc chlorothalonil report
As reported recently, Teagasc produced a report on the contribution and importance of CTL to disease control programmes in Irish winter wheat and winter and spring barley.
CTL is very important in winter wheat for its contribution to the control of septoria tritici and also for the control of ramularia in winter and spring barley.
This report, entitled An evaluation of the potential impact the loss of chlorothalonil may have on the productivity of winter wheat and spring and winter barley grown in Ireland, was compiled by Teagasc’s Steven Kildea, John Spink and Michael Hennessy. It looks at the contribution of chlorothalonil to yield in these crops, mainly in recent years when sensitivity changes existed in the fungal pathogens.
An examination of all past usable results, which allow comparisons of treatment performances, showed the actual yield differences and the impact of those differences (+/- CTL) on the economics of crop production.
Economic parameters, such as the impact on cost per tonne and net margin, were also examined using both data from Crop Costs and Returns and Teagasc’s e-profit monitor and analysed for different categories of growers. Basically, the report looked at the impact for the sector if CTL cannot be included in fungicide programmes.
The report only deals with the output consequences for growers. It does not take into account wider ramifications, such as impact on grain quality, the potential loss of cereal area, possible area swaps to alternative crops, etc.
The analyses were mainly conducted on results from the 2016 and 2017 seasons, with some 2018 data used in the case of barley to reflect the most recent changes in fungicide resistance in ramularia.
The impact on wheat
Strains of septoria are now known to exist which are less tolerant to the SDHI family – the last currently available family that showed high selective activity. These strains are likely to increase to a higher level in the population unless we can utilise a second family to help control.
If resistance expands, CTL will be the only remaining product that can show reasonable activity against septoria, albeit totally preventative.
It now seems inevitable that the use of CTL in fungicide mixtures in past years is likely to have slowed the pace of resistance development. CTL now accounts for a higher proportion of the yield benefit that results from fungicide use.
The report examined a total of 17 trials which provided 55 direct comparisons for the presence or absence of CTL. In all cases, Bravo 500 was applied at 1.0 l/ha. Most treatments involved available fungicides (SDHI/azole mixtures) applied at 80% to 100% of recommended label rate.
While this report concentrated on grain yield effects, the authors comment that there is a strong correlation between septoria infection and yield loss, which is reflective of disease control.
The wheat data found that the addition of CTL to fungicide programmes added a significant 0.58t/ha on average yield, ranging from 1.73t/ha to -0.25t/ha.
Also, 51 of the 55 comparisons were positive for yield benefit. The four negative responses related either to product antagonism in mixtures or its inclusion with a new highly active development product.
On balance, the addition of CTL in mixes added yield and profit and so lost yield and profit were generally associated with its exclusion. The economic cost of not having CTL in mixtures is most acute at lower yield levels, as it increases cost per tonne and decreases net margin.
The report suggested an increase of between 8% and 12% in the cost per tonne where CTL is not included. And this could mean a reduction of over 50% in net margin. However, if full resistance develops to the SDHI fungicides the yield loss and margin impacts would be much greater.
Barley – ramularia specific
Data from winter and spring barley trials for 2016 and 2017 was also examined, with some information from 2018 also. This enabled the analysis of data from nine trials with 14 usable comparisons of +/- CTL. Bravo 500 was again applied at 1.0 l/ha. Comparisons were made with current market standards applied at 50% to 60% of recommended rate.
Most comparisons were made at the final application (GS39-59) stage. Similar data was collected and analysed as with winter wheat.
The response to the inclusion of CTL was broadly similar in winter and spring barley and the average increase recorded was 0.35t/ha, which was barely significant. As both crops behaved in a similar way, only spring crop data was used in this analysis.
The yield response to the addition of CTL ranged from 1.37t/ha to -0.57t/ha and was positive in 12 of the 14 comparisons. That said, the authors stress that increased weight should be given to the limited data from 2018, as resistance to both SDHIs and azoles was emerging at that point.
Of the four comparisons from 2018, two showed a response above 1.0t/ha with the other two showing a response of 0.6t/ha and 0.2t/ha. These differences appear to relate more to variety and so varietal resistance must be highlighted.
The report indicates that yield loss in barley, in the absence of CTL, is likely to be between 5% and 11% and with production cost per tonne of spring barley (without CTL) increasing by between 5% and 11%. But it also estimates that net margins could be decreased by a substantial 65% in the absence of CTL.
If chlorothalonil is not available the report estimates a possible average net margin reduction of over 50% in wheat and 65% in barley based on national average yields.Cereal production will only be economic on the highest yielding sites with low costs of production.Irish growers will lose competitiveness as cost per tonne produced increases.Any new fungicides will be increasingly vulnerable to resistance development if they do not have robust protection from products like chlorothalonil.
Grain growers will now be very aware of the risks to the ongoing availability of chlorothalonil (CTL). Best known as Bravo and available as many different brand names, chlorothalonil has been key to successful disease control in wheat and barley in this country for the past few decades. A Teagasc report estimates that net margins could be hit by more than 50% if it is removed.
The active was up for its routine re-registration in October of this year. Changes to its use seemed inevitable. A rate reduction was anticipated, coupled with the likelihood that the maximum dose rate would apply to the active rather than any individual product. But as we got into 2018, the possibility of non-registration seemed more likely.
Case to answer
The registration process indicated that CTL had a case to answer on a number of fronts. Current registration criteria are now based on potential hazards, rather than the risk management of past registrations.
The main concerns would appear to be its alleged carcinogenicity (capacity to produce cancer) and a suggested risk to ground water.
It may be possible to challenge the risk to ground water, in that there has not been talk of such problems occurring in practice, in spite of its extensive use for decades.
But its label has long carried the alleged limited carcinogen rating and this is now a major issue.
We understand that CTL is once again being evaluated by competent European authorities and that this examination is currently causing the delay in the decision, which may now be delayed possibly until December.
It seems inevitable that the results of this test will seal the fate of CTL one way or the other. When we demand that science be the arbitrator of decisions relating to chemicals, we will have little choice but to accept the decision of science in this outcome.
The greater problem has to be the failure of the registration system to take into account the importance of this active for farmers in this part of the world and the failure to have a satisfactory replacement in place in the event of a ban.
Teagasc chlorothalonil report
As reported recently, Teagasc produced a report on the contribution and importance of CTL to disease control programmes in Irish winter wheat and winter and spring barley.
CTL is very important in winter wheat for its contribution to the control of septoria tritici and also for the control of ramularia in winter and spring barley.
This report, entitled An evaluation of the potential impact the loss of chlorothalonil may have on the productivity of winter wheat and spring and winter barley grown in Ireland, was compiled by Teagasc’s Steven Kildea, John Spink and Michael Hennessy. It looks at the contribution of chlorothalonil to yield in these crops, mainly in recent years when sensitivity changes existed in the fungal pathogens.
An examination of all past usable results, which allow comparisons of treatment performances, showed the actual yield differences and the impact of those differences (+/- CTL) on the economics of crop production.
Economic parameters, such as the impact on cost per tonne and net margin, were also examined using both data from Crop Costs and Returns and Teagasc’s e-profit monitor and analysed for different categories of growers. Basically, the report looked at the impact for the sector if CTL cannot be included in fungicide programmes.
The report only deals with the output consequences for growers. It does not take into account wider ramifications, such as impact on grain quality, the potential loss of cereal area, possible area swaps to alternative crops, etc.
The analyses were mainly conducted on results from the 2016 and 2017 seasons, with some 2018 data used in the case of barley to reflect the most recent changes in fungicide resistance in ramularia.
The impact on wheat
Strains of septoria are now known to exist which are less tolerant to the SDHI family – the last currently available family that showed high selective activity. These strains are likely to increase to a higher level in the population unless we can utilise a second family to help control.
If resistance expands, CTL will be the only remaining product that can show reasonable activity against septoria, albeit totally preventative.
It now seems inevitable that the use of CTL in fungicide mixtures in past years is likely to have slowed the pace of resistance development. CTL now accounts for a higher proportion of the yield benefit that results from fungicide use.
The report examined a total of 17 trials which provided 55 direct comparisons for the presence or absence of CTL. In all cases, Bravo 500 was applied at 1.0 l/ha. Most treatments involved available fungicides (SDHI/azole mixtures) applied at 80% to 100% of recommended label rate.
While this report concentrated on grain yield effects, the authors comment that there is a strong correlation between septoria infection and yield loss, which is reflective of disease control.
The wheat data found that the addition of CTL to fungicide programmes added a significant 0.58t/ha on average yield, ranging from 1.73t/ha to -0.25t/ha.
Also, 51 of the 55 comparisons were positive for yield benefit. The four negative responses related either to product antagonism in mixtures or its inclusion with a new highly active development product.
On balance, the addition of CTL in mixes added yield and profit and so lost yield and profit were generally associated with its exclusion. The economic cost of not having CTL in mixtures is most acute at lower yield levels, as it increases cost per tonne and decreases net margin.
The report suggested an increase of between 8% and 12% in the cost per tonne where CTL is not included. And this could mean a reduction of over 50% in net margin. However, if full resistance develops to the SDHI fungicides the yield loss and margin impacts would be much greater.
Barley – ramularia specific
Data from winter and spring barley trials for 2016 and 2017 was also examined, with some information from 2018 also. This enabled the analysis of data from nine trials with 14 usable comparisons of +/- CTL. Bravo 500 was again applied at 1.0 l/ha. Comparisons were made with current market standards applied at 50% to 60% of recommended rate.
Most comparisons were made at the final application (GS39-59) stage. Similar data was collected and analysed as with winter wheat.
The response to the inclusion of CTL was broadly similar in winter and spring barley and the average increase recorded was 0.35t/ha, which was barely significant. As both crops behaved in a similar way, only spring crop data was used in this analysis.
The yield response to the addition of CTL ranged from 1.37t/ha to -0.57t/ha and was positive in 12 of the 14 comparisons. That said, the authors stress that increased weight should be given to the limited data from 2018, as resistance to both SDHIs and azoles was emerging at that point.
Of the four comparisons from 2018, two showed a response above 1.0t/ha with the other two showing a response of 0.6t/ha and 0.2t/ha. These differences appear to relate more to variety and so varietal resistance must be highlighted.
The report indicates that yield loss in barley, in the absence of CTL, is likely to be between 5% and 11% and with production cost per tonne of spring barley (without CTL) increasing by between 5% and 11%. But it also estimates that net margins could be decreased by a substantial 65% in the absence of CTL.
If chlorothalonil is not available the report estimates a possible average net margin reduction of over 50% in wheat and 65% in barley based on national average yields.Cereal production will only be economic on the highest yielding sites with low costs of production.Irish growers will lose competitiveness as cost per tonne produced increases.Any new fungicides will be increasingly vulnerable to resistance development if they do not have robust protection from products like chlorothalonil. 
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