Bayer confirms that ramularia is resistant to most fungicide chemistries

A recent finding suggesting that the barley disease ramularia is potentially resistant to three of the main groups of fungicide chemistry in Germany is a warning to Irish growers, according to Teagasc Tillage Advisor Eamonn Lynch.

“It’s a disease that can rear its head in certain years,” he explained.

This could be a real issue for the tillage sector in the future. The resistance threat could significantly reduce the range of fungicides that can be used to tackle a disease, that is of real significance in this country.

Bayer resistance testing in southern Germany has confirmed the presence of two new mutations – one that impacts the performance of SDHI fungicides, and another that affects azole fungicides. Resistance in ramularia to strobilurins has previously been confirmed.

The mutation discovered in the target site for azoles has been found to severely impact the performance of all ‘actives’ in this group. This is unlike the mutations to azoles found in septoria, which incur a loss in sensitivity resulting in a slide in efficacy, rather than a significant drop in performance.

In addition, the SDHI mutation has led to full resistance to all members of that group of chemistry.

Where these mutations have been found no SDHI or azole fungicide will now control ramularia, even when used at full rates. It leaves chlorothalonil as the only remaining effective chemical option for control of the disease.

German authorities are now advising farmers to use of chlorothalonil in all applications in barley.

According to Bayer, the use of chlorothalonil at the T2 timing will give the best boost to ramularia control, and help protect other products where ramularia is sensitive to other chemistry. For future years, using cultural controls for ramularia, such as avoiding the use of farm-saved seed from crops that had ramularia infections and using more resistant varieties, particularly in higher risk areas, will make sense.

Last year, ramularia was particularly severe in mainland Europe. Threat levels rise throughout periods of cold, wet weather during the month of June.