Disease experts in Ireland have identified new strains of septoria tritici with reduced sensitivity to SDHI fungicides, one of the key fungicide groups providing control of the disease.
The discovery comes amid concerns over declining efficacy seen in recent seasons of triazole fungicides, another key component of septoria control programmes.
The most insensitive of these strains have been found at a low frequency at Irish food and agriculture authority Teagasc’s Oak Park site in Carlow following routine sampling at the end of the 2015 season.
In laboratory tests these strains are said to have survived up to 100 times the concentration of SDHI fungicides compared to the most insensitive strains found in previous years. Subsequent analysis of these isolates confirmed the presence of a mutation in the SDHI target site.
According to Teagasc, an additional as yet unidentified strain showing reduced sensitivity, although not as extreme as those found at Oak Park, was also identified in a crop in the north east of the country. These strains have not previously been found in field populations and therefore their fitness (their ability to survive the winter) remains unknown.
John Spink, head of the Teagasc crops science department says: “Further research is on-going to examine the potential impact of these strains on disease control, while intensive nationwide monitoring is planned for early spring.”
Given the low frequency at which these strains have so far been found, it is expected good septoria tritici control will still be possible with SDHI fungicides in the coming season, says Teagasc.
However, any increase in their frequency will threaten the future efficacy of this group of fungicides and so it is vital all farmers use good anti-resistance practices.
Teagasc plant pathologist, Steven Kildea says: “Despite recent declines in the efficacy of azole fungicides they are still an integral part of fungicide programmes for both disease control and as an anti-resistance partner. Therefore, for the coming season; SDHIs should only be used in mixture with a robust rate of azole and a multisite fungicide, and should never be applied more than twice during the season.”
According to Fiona Burnett, SRUC plant pathologist and chairman of FRAG (Fungicide Resistance Action Group )-UK, the findings underline the need for growers to follow stewardship guidelines to protect both triazole and SDHI fungicides.
Monitoring conducted by Rothamsted Research in the UK during 2015 has also identified the presence at low frequencies of septoria isolates with reduced sensitivity to SDHIs.
“I think people have been thinking ‘when is this going to happen?’ rather than if,” says Professor Burnett.
The FRAG-UK resistance management in cereals guidelines are available here