Yellow rust will strike, warns ADAS wheat disease expert

All winter wheat varieties previously susceptible to one of the two main races of yellow rust are also susceptible to the new “Solstice” strain, NIAB analysis has found.

In addition, four varieties, Solstice, Humber, QPlus and Viscount, that were resistant to the Robigus and original V6 races, are also susceptible.

But other varieties, such as Cordiale, JB Diego, Alchemy and Claire were resistant to all three races, according to Rosemary Bayles of NIAB.

“The Solstice race is virulent on four key varietal yellow rust resistances,” she told advisers. Previous races could only overcome or two of those resistances.

Nearly 60% of the 2010 wheat crop, including Oakley, was susceptible to the Solstice race, which she was certain would “dominate” in 2010.

“It means the scope for diversification has been drastically reduced, and the safest option will be to grow varieties with high resistance ratings as companions to susceptible varieties,” she said.

Sowing decisions had been made for this season, she said, but diversification tables would still be useful to help work out the risks of spread between varieties and to prioritise disease control strategies.

Winter weather would determine the severity of any outbreak, Jonathan Blake, an ADAS plant pathologist, said.

“It is not a case of will it strike, but how quickly,” he warned.

Last year there had been a significant epidemic despite a colder winter that would usually reduce inoculum, he noted. “Does that mean the new race has increased aggressiveness. If it does it has implications on how to manage crops in the future.”

HGCA fungicide performance trials on Robigus suggested that Opus (epoxiconazole) and Brutus (epoxiconazole + metconazole) were ahead of Proline (prothioconazole) against the disease.

“But most products are pretty good against yellow rust. Choosing the right moment to start and the correct interval between treatments might be equally or more important than product choice.”

In the septoria trials Opus and Proline remained almost impossible to separate on performance, while Brutus “looked strong.” “But you have to remember it is a heavily loaded azole. A better comparison is a half dose of Brutus against a full dose of Opus.”

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