Continued changes in yellow rust pathogenicity over the past season mean that almost two thirds of mainstream winter wheat varieties have a lower resistance to the disease than their current Recommended List ratings suggest, according to the latest information from the Agrii National Cereal Disease Survey.
Monitoring across the extensive series of national variety trials and tussock plots at Agrii Technology Centres and iFarms throughout the country over 2017 reveals that no less than 23 of today’s 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.
It also shows that half the six main candidate varieties are noticeably more susceptible to the disease than official figures indicate, providing a timely early warning ahead of 2017/18 planting.
“A number of varieties are holding their resistance ratings well, with 11 still scoring 8.0 or more in our national survey,” reports Agrii R&D manager, Jim Carswell.” However, our monitoring also shows many have become noticeably more susceptible to yellow rust over the past season, several seeing their resistance ratings fall by two or more full points.
“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 is only to be expected with varieties that have been widely grown for a number of years. 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 will do much to reduce the yellow rust pressure on varieties,” he continued. “As will well-balanced micro-nutrition to promote the healthiest crops. And, despite the withdrawal of the fluquinconazole seed treatment that was such a good early defence, in the majority of cases infections remain eminently controllable with the in-crop chemistry still available.
“We know how rapidly the disease can take-off, though, and how devastating losses can be when conditions are in its favour or the weather gets in the way of the most timely spraying. So it’s especially important to go into the season knowing exactly the level of risk the varieties we’re growing present. Especially so with such a large area of wheat almost certain to go into varieties with real yellow rust resistance levels of 6.0 or less this autumn.
“Armed with the extra intelligence the Agrii Advisory List provides on a wide range of agronomic essentials and the special yellow rust diversification scheme we have developed with the national authority on the disease, Dr Rosemary Bayles, our agronomists and growers can make the best-informed choices for their main sowing slots,” Jim Carswell concluded.
“They can also keep a particularly close eye on varieties in their planting mixes posing a markedly greater risk than their RL yellow rust ratings suggest, and better prioritise their most susceptible crops for robust treatment should conditions prove favourable for disease development in 2018.”
