Low resistance risk fungicide programmes must be adopted universally to prolong the efficacy of cereal chemistry, delegates heard at the 2017 AHDB Agronomists’ Conference.
The message came following the annual update to AHDB’s fungicide performance data, which showed a continued slide in fungicide efficacy in several key UK cereal pathogens.
AHDB also announced it would work more closely with the Fungicide Resistance Action Group UK (FRAG) to communicate anti-resistance management information, via a new initiative called Fungicide Futures.
Wheat septoria shifts
Speaking at the conference, ADAS’ Jonathan Blake said although SDHIs remained highly active against septoria, there was increasing evidence of mutant strains with reduced sensitivity and indications of changes in efficacy in trials.
Septoria isolates with reduced sensitivity to SDHIs are now believed to be widespread in the UK and Ireland. Research, funded by AHDB and fungicide manufacturers, however, demonstrates clearly that resistance development and spread can be slowed through good management. SDHIs, when used, should be combined with robust azole rates and multisite chemistry. Some SDHI mutants appear only to survive under high SDHI selection pressure, so only applying SDHIs when really needed, along with good resistance management, should help to prolong their efficacy.
More encouraging news was given on azole activity against septoria, as long-term monitoring suggests the decline in efficacy could be stabilising. Resistance management efforts for azoles should, however, be maintained. Balanced mixtures and the use of multisite chemistry are required for good stewardship. Extra ‘inserted’ sprays, such as T0 and T1.5, should be avoided, unless absolutely necessary.
Barley disease shifts
Changes in sensitivity to SDHIs and azoles in ramularia populations were confirmed in Scotland (by SRUC) and Germany (by Bayer) in April. Jonathan said the field efficacy of SDHIs and azoles had been severely affected at fungicide performance and SRUC trial sites in Scotland in 2017. Only chlorothalonil, alone or in mixtures, remained effective and the advice was to include it at T2 spray timings.
In February, AHDB announced that mutated UK net blotch isolates less sensitive to SDHIs had been detected at a fungicide performance trial site at high enough frequencies to raise concerns about efficacy. The decline in efficacy was confirmed at the conference. Delegates were told mixture products gave the strongest performance in trials and to use them to protect against further declines in efficacy.
The activity of strobilurins against rhynchosporium also appears to have declined over the last 15 years. They still, however, provide a useful option to add efficacy and protect chemistry in mixtures and to diversify fungicide programmes.
With efficacy concerns increasing in cereal production, a team of expert panellists took part in a debate to get to the heart of resistance guidance and the associated practical constraints.
The panellists agreed the current approach was not fit for purpose and that pesticide survey figures suggest usage does not appear to fluctuate in response to seasonal risk. The use of ‘insurance sprays’ was cited as a key pressure point and more needed to be done to give people the confidence to apply fungicides only in proportion to the risk.
The panel discussed ways to reduce the use of SDHIs and stressed they should not be the default choice at T1. It was stated how integrated measures, such as combining resistant wheat varieties with a later sowing date, could reduce septoria pressures and allow azole plus multisite choices to be used instead.
The use of real-time disease pressure information – from technology such as in-field biosensors – could revolutionise spraying in the future, according to the panel, as it would allow field-level risks to be better quantified. In the meantime, walking crops and responding to the disease pressure observed remains critical.
Paul Gosling, who manages disease work at AHDB, said: “The panel debate made it clear the key to success is to promote management that combines good control with best resistance management practice.
“That’s why we’ve introduced our new Fungicide Futures initiative, as it will cut through resistance management science and provide timely guidance, which takes both seasonal pressures and resistance risks into account.
“A key take-home message from the debate was it doesn’t makes sense to have a fixed spray programme. To protect efficacy, programmes must respond to risk and, when a spray is required, chemistry must be protected with different modes of action in mixtures combined with alternating chemistry, where practical.”