Early this year crop protection company Bayer announced that in Germany and Denmark crops infected with the Ramularia collo-cygni fungus were not responding to normal fungicide treatments containing triazole and SDHI fungicides.
The SRUC studies indicate Scottish barley faces a similar threat if farmers do not make adjustments to their treatments.
Ramularia collo-cygni causes Ramularia Leaf Spot Disease which as well as posing a particular problem in spring sown crops also affects production in autumn sown crops. Farmers have used a well established protection regime based on triazole and SDHI fungicides but testing in Scotland by SRUC has revealed a significant shift in the sensitivity of the fungus to both of these chemicals between 2012 and 2016.
“Unless farmers take action there is a real risk that the fungicide resistant Ramularia strains will build up causing major problems in future, comments Senior Plant Pathologist Dr Neil Havis. “But our research shows that the fungus is still sensitive to cholorothalonil so we are recommending farmers add cholorothalonil into their spraying programme, particularly at the T2 spray timing.”
However SRUC experts continue to warn against over reliance on one set of substances when they are suspected to be at risk. Combinations of chemicals, which include multisites, coupled with alternative strategies such as using varieties with known disease resistance, have proved best against infection from fungal diseases.
“Few treatments are guaranteed fully effective on their own” says Dr Havis. “Using just one fungicide with one mode of action risks resistant strains to multiply and gather strength without the competition from other isolates. If those are also resistant to the other chemicals in our armoury we risk a disease explosion, if not this season next season. Biology means diseases are always evolving and we need every strategy to try to keep up.”
With many crops due to have a spray at the T2 stage SRUC recommend growers consult their advisor or agronomist to decide their most effective treatment.