Sunday, November 19, 2017

Survey highlights changes in yellow rust resistance

October 4, 2017 by  
Filed under Crops

Rosemary Bayles & Jim Carswell examine tussock plots at AgriiFocus - 2

Most mainstream winter wheat varieties have a lower resistance to yellow rust than Recommended List ratings suggest, reveals the latest Agrii National Cereal Disease Survey.

Continued changes in yellow rust pathogenicity over the past season mean almost two thirds of wheat varieties are less resistant to the disease, according to the most up-to-date information from the survey.

Some 23 of 36 main winter wheat varieties (64%) have a lower yellow rust resistance than their 2017/18 RL ratings, with 15 of these being at least a point lower, according to Agrii Technology Centres and iFarms monitored during 2017.

More susceptible

Half of the six main candidate varieties are noticeably more susceptible to the disease than official figures indicate – providing growers with a timely early warning ahead of 2017/18 planting, says Agrii research and development manager Jim Carswell.

“A number of varieties are holding their resistance ratings well, with 11 still scoring 8.0 or more in our national survey. However, our monitoring also shows many have become noticeably more susceptible to yellow rust over the past season.”

Several varieties have seen resistance ratings fall by two or more full points, said Mr Carswell. “Overall, the latest Agrii advisory list we produced to complement the RL now rates nine of the mainstream wheat varieties at less than 5.0 for yellow rust resistance and five at less than 3.0.”

A progressive fall-off in resistance was only to be expected with varieties that had been widely grown for a number of years, said Mr Carswell.

But he added: “More worryingly, though, we’ve recorded seven of the 11 new varieties on the RL, as well as several candidates with yellow rust resistance scores at least a point lower than their official ratings suggest.”

Later sowing would do much to reduce yellow rust pressure on varieties, as would well-balanced micro-nutrition to promote the healthiest crops.  And, despite the withdrawal of fluquinconazole seed treatment, most infections remained controllable with in-crop chemistry still available.

But the disease could still take off rapidly, with devastating losses when conditions were in its favour or the weather prevented timely spraying. This meant an accurate assessment of risk was particularly important.

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