Choose actives carefully to counter brown rust – Farmers Weekly

Brown rust has infected wheat crops very early this season due to a mild wet winter followed by the warmest May on record, as the disease spreads quickly in wet and warm conditions.

Dr Aoife O’Driscoll, crop protection specialist at consultant Niab, said with inoculum overwintering and early fungicide sprays being missed due to the wet spring weather, favourable weather conditions had allowed the disease to spread rapidly.

In reaction, she is now looking to focus growers’ attention on specific actives rather than broad-spectrum products to control infections, and in the case of brown rust, the disease can cycle quickly in five or six days during warm weather. “We are encouraging growers to think about actives rather than products, and then look at the strengths and weaknesses of each active,” she told Farmers Weekly.

Aoife suggested growers look carefully at which actives had an effect on each disease, such as brown and yellow rusts and also septoria, while pointing out there is a new winter wheat variety which is the first to show both juvenile and adult brown rust resistance.

Some growers struggled to distinguish brown rust and yellow rust in the early spring, as the last time brown rust appeared so early was 2007. However, climate change could make mild winters and warm wet springs more prevalent. Many failed to get a TO spray applied in late March, but if conditions are favourable and brown rust is a threat, Aoife suggests a spray of a strobilurin would be a good choice, or tebuconazole if yellow rust is the bigger threat.

She points out that for T1 and T2 timings, if brown rust is a threat then growers should look to choose an SDHI with the best possible activity against the disease, such as Solatenol or Iblon, supported by an appropriate azole. If other products are used, such as Adepidyn or Inatreq, then extra rust control may be needed in a high disease season.

The T3 ear spray is advised to be based around a strobilurin and tebuconazole, with prothioconazole added for fusarium. She suggests strobilurins are best used early and late in the season, so at T0 and T3.

Variety selection is being made more complicated by diseases popping up nationwide rather than rusts in the East and septoria in the West, while drilling date is always a compromise, with late drilling good to limit septoria but possibly encouraging rusts.

A good compromise could be drilling in the second half of October, while she pointed out that the variety Goldfinch looked interesting as a new variety as it had both juvenile and adult brown rust resistance.

Lee Bennett, managing director at the variety’s breeder, RAGT, said this wheat variety could be especially important when the threat of brown rust was severe. “Goldfinch is the cleanest wheat variety that farmers can grow,” he said.

The Group 2 milling variety comes up for possible inclusion in the AHDR Recom- mended List (RL) later this year, and Lee added that the variety had resistance scores of 9 for yellow and brown rusts, 8 for mildew and 7 for septoria, in a 1-9 scoring range where 9 shows good resistance and 1 is very susceptible. The variety, like all recent RAGT products, has resistance to barley yellow dwarf virus and also to orange wheat blossom midge, like Wolverine and Grouse.

“We’ve not seen brown rust in May for a long time, and it has largely been seen as a hot weather disease that comes into crops in late June and early July,” he said.

Many varieties have moderate resistance scores for brown rust ranging from 5 to 7, such as the popular varieties Dawsum (7), Extase (6) and Champion (5), while Skyfall stands out as the only 9 on the RL and Crusoe has a lowly 3.