A dramatic shift in the sensitivity of Ramularia leaf spot fungus to leading fungicide chemistry means barley growers must take extra care with spray timings and product selection.
Bayer identified two mutations, one causing resistance to the SDHI fungicide group while a second target site mutation significantly reduced azole activity. Ramularia resistance to strobilurins has previously been confirmed, so three major fungicide groups now offer limited control in winter and spring barley where resistance is present.
Anyone growing barley should assume Ramularia is a threat which cannot be fully controlled with SDHI, triazole or strobilurin-based chemistry alone.
No resistance has been found to the broad spectrum fungicide chlorothalonil, so this is essential for controlling Ramularia. T2 is the key timing.
Although the dramatic resistance development presents challenges for Ramularia control, sensitive populations are still present in the UK, so not all crops will be affected.
Products like SiltraXpro remain effective where there is no resistance, although should be used with CTL for resistance management.
Even trials under very high disease pressure last year in Suffolk found a two-spray programme of SiltraXpro without CTL still delivered 50-60% Ramularia control, although by adding CTL this increased to 90%. Bixafen also aids greening, which improves crop health, he adds.