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Alternating triazoles against resistance in beets
Alternating the available triazoles in sugar beet cultivation is an absolute necessity. That is the conclusion of the resistance study that Bayer had carried out last year by Epilogic in Germany.
In the Netherlands there is general resistance of strobilurins to Cercospora. That is why growers rely on triazoles to combat this leaf fungus. Strobilurins remain valuable for the control of other leaf fungi. These make a positive contribution to the ultimate sugar yield due to the 'greening effect' (stronger crop).
A total of 25 samples were examined to test the resistance susceptibility of the four triazoles used in the beets. These came from 16 locations across the Netherlands.
Cyproconazole in Sphere remains indispensable
The research shows that in particular products based on difenoconazole (in Spyrale, Score, Borgi, Difure solo and Difure Pro) show a high degree of 'shifting' and can therefore have a strongly reduced effect against Cercospora. The study also shows that cyproconazole (in Sphere), propiconazole (in Difure Pro) and to a lesser extent epoxiconazole (in Retengo Plust and Opus Team) are less sensitive to 'shifting' and therefore have retained their strong activity against these Cercospora isolates. .
Variety essential
It can be concluded from the results that alternating the available triazoles is an absolute necessity. All available triazoles are needed to prevent further 'shifting' in the control of Cercospora. Alternating agents containing the same triazoles is not alternating and is therefore strongly discouraged.
The study results are in line with the results of the IRS's extensive field study and resistance study of isolates from 2018, as recently published in the report Cercospora control in sugar beets.
How was resistance susceptibility measured?
The susceptibility of the isolates to triazoles is expressed in the EC 50 value. This is the measure at which 50% of the fungus is killed in vitro and at a specified exposure time. The value mEC50 (mean EC50) indicates the mean of the individual isolates examined. Each active substance has its own intrinsic (specific) EC50 value. To compare agents, this value is therefore divided by the EC50 value of a sensitive reference strain. This creates the mean (mean) Reference Factor (mRF). The higher this number, the greater the chance of 'shifting' (occurrence of reduced sensitivity). For the evaluation of the isolates it is assumed that isolates with an mRF higher than 30 are less sensitive.
Table 1. Results Monitoring Samples 2018 by Epilogic
