Yellow rust monitoring prompts variety alert Wheat growers across northern England and eastern Scotland must be alert to changes in yellow rust virulence that are making variety resistance ratings from even a year ago unreliable. This was the clear warning from Agrii northern research and development manager, Jim Carswell’s monitoring of untreated variety trials and specialist tussock plots at the company’s main Bishop Burton and Carnoustie R&D sites. “The past two seasons, in particular, have taught us that yellow rust is very far from just a disease of southern and eastern England,” he stressed in the wheat plot tour at Agrii’s Northern Crop Technology Centre, Bishop Burton College earlier this summer. “Infection levels in untreated plots were massive at Bishop Burton last season. While less problematic here this year, they’ve been very heavy on the Angus coast at Carnoustie. “The real issue for growers, though, is the speed with which the disease appears to be changing. This is much more rapid than I’ve ever known. It means we’re seeing varieties like Zulu that continue to be rated 9 for yellow rust resistance on the Recommended List showing significantly more signs of infection than expected.” Indeed, 32 of the 49 current and up-and-coming varieties in Agrii’s Bishop Burton untreated plots have shown signs of yellow rust this season. More worryingly, this includes just over half the 17 Recommended and Candidate varieties with current RL resistance scores of 9 being grown. And only one of the eight Candidate varieties rated 9 for yellow rust in the trials at Bishop Burton and Carnoustie is showing no sign of the disease in mid-summer assessments.
“Our parallel tussock plot trials with 25 indicator varieties covering all the main resistance sources are highlighting the wheat genetics at most risk from the changing virulence levels,” Jim Carswell noted. “Interestingly, across the nine sites in our national network, we’ve seen little or no evidence of infections of Kranich so far this season. Equally, only at Carnoustie have we recorded significant infections on Warrior. So the situation is clearly more complex than just the development of either of these two ‘headline’ races. “Whatever the precise genetic basis for what we’re seeing across the country, the pace of current yellow rust change really underlines the need for variety decisions to be based on resistance scores from the current season rather than just more historic RL data,” he insisted. “Once this season’s monitoring is completed, we shall be up-dating the yellow rust ratings in the Agrii Wheat Advisory List we produce as a complement to the Recommended List to give our agronomists and growers the best available intelligence well ahead of wheat drilling.” In addition to enabling growers to focus their 2017 cropping on lower risk varieties and/or spread their risk with a range of varieties, Jim Carswell pointed out that this will better inform seed treatment choice, drilling date and fungicide decision-making. He strongly recommended fluquinconazole seed treatment, later drilling and early fungicide treatment as risk management tools where varieties with doubtful yellow rust ratings or ancestries that make them especially susceptible to breakdown are grown. At the same time, he stressed the importance of
Agrii adviser Jim Carswell in the wheat plots.
not being pushed into unnecessary action by juvenile susceptibility. “Revelation is a case in point here,” he explained. “It can easily show signs of yellow rust in the winter, but continues to be almost completely free from the disease in our adult crop monitoring.”
Organic matter improvement Relatively small improvements in soil organic matter can make all the difference to soil health and, with it, workability, water regulation and crop nutrition, explained Lancrop Laboratories specialist, Jon Telfer (right) at the Agrii event. However, he pointed out that there is little improvement in nutrient return at soil organic matter levels of more than 4–5 per cent, while different sources of organic matter have very different effects on short-term nutrient supply. Under these circumstances, he urged all those wanting to improve long term soil health and resilience while maintaining immediate crop performance to understand both the level of organic matter they
actually have in their soils and the composition of any materials available to increase it. “It’s invariably a false economy to try managing what you can’t measure,” Mr Telfer stressed. “Especially as the organic matter determination we provide as a bolt-on to the standard soil analysis service offered through Agrii is both easy and inexpensive. As a rule, Jon Telfer regards a Dumas combustion soil organic matter level of three per cent or more as adequate in most cases. Where the level is less than this, he sees efforts to boost it likely to be particularly rewarding. If growers are not to disadvantage their immediate cropping in pursuit of longer-term soil health gains, though, he is adamant they need to be aware of the carbon to nitrogen ratios of the organic manures they’re using. “Soil health improvement is a vital consideration for many growers these days. But it needs to be done with care and understanding in a well-balanced approach,” he concluded. ■
24 www.farmersguide.co.uk August 2016
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Published on Aug 4, 2016