Disease experts have described the latest septoria monitoring results, which confirm the presence in the UK of isolates with a high level of resistance to SDHIs, as being at the ’worst end’ of expectations.
A small number of septoria tritici isolates, collected at sites in the UK in 2015, have been confirmed as being highly resistant to SDHI fungicides, according to AHDB Cereals & Oilseeds-funded work.
The latest results come from tests on susceptible seedlings in a glasshouse using field rates of straight SDHI fungicides.
The findings are in line with laboratory test findings reported by AHDB earlier this year.
The screening work, which is led by Rothamsted Research, also confirmed the presence of mutations in the three genes involved in the binding of SDHIs to their target site.
The frequency of these highly resistant isolates was extremely low in the UK population in 2015.
Even where such isolates are found in commercial crops, considerable uncertainty about their potential to cause economic harm remains, says AHDB.
In the field, varietal resistance and weather conditions – along with activity from effective mixing partners – influence the efficacy of SDHIs.
Further monitoring is also in progress to establish if there are fitness costs associated with these SDHI resistant field strains.
Although good control of septoria from SDHIs is still anticipated in 2016, the ability of these new highly resistant mutated strains to survive and increase is a considerable cause for concern, growers and agronomists are being advised.
The results provide the most important warning shot yet about the need to work together to protect fungicide efficacy.
AHDB has worked with the Fungicides Resistance Action Group (FRAG-UK) to provide and promote evidence-based, independent and practical information on resistance management.
Dr Paul Gosling, who manages resistance research at AHDB, says: “The latest results are toward the worst end of our expectations.
“They confirm, more than ever, that it is critical to adopt best resistance management practices to slow the spread of these strains and maximise the effective lifespan of the SDHIs.”
Prof Fiona Burnett, chair of FRAG-UK, says: “It is imperative that the whole industry acts together to actively manage this situation.
“We’ve updated the FRAG-UK guidelines, which emphasise the need to use SDHIs with robust azole doses and to include the use of multisites in programmes.’’