‘Low resistance risk fungicide programmes must become the norm’

Low resistance risk fungicide programmes must be adopted universally to prolong the efficacy of cereal chemistry in the UK, delegates heard at the 2017 AHDB Agronomists’ Conference.

The message came following the annual update to Agriculture and Horticulture Development Board (AHDB) 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, through a new initiative called ‘Fungicide Futures’.

Wheat septoria shifts

Speaking at the conference, ADAS’ Jonathan Blake said although succinate dehydrogenase inhibitor (SDHI) fungicides 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 SDHI fungicides are now believed to be widespread in the UK and Ireland.

However, research – funded by AHDB and fungicide manufacturers – demonstrates clearly that resistance development and spread can be slowed through good management.

SDHIs, when used, should be combined with robust azole rates and multi-site 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 be maintained, however. Balanced mixtures and the use of multi-site chemistry are required for good stewardship.

Delegates were advised 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.

Blake said the field efficacy of SDHI fungicides 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.