Heightened disease threat means that a T0 is even more essential says agronomist

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Growers must view the T0 as a standard part of their fungicide programme, particularly on high yield potential wheats.

That’s the view of nationwide agronomy business, Zantra’s, technical director, Chris Bean, who says that it is the key to getting on top of increasingly problematic yellow rust and also Septoria.

He points out major changes to yellow rust disease resistance ratings, which were only confirmed after growers had selected and drilled varieties, will necessitate a change in strategy for many.

“A wide range of varieties will be under increased pressure from new and existing yellow rust races in 2017 and growers should consider the disease a potential threat to all wheats this spring,” he stresses.

“Our experience is that the new strains now being found – usually in mixture with older strains of yellow rust – produce more pustules leading to an increased numbers of spores and are adapted to survive under more extreme conditions.

“So, don’t be fooled into thinking that recent frosts will have helped check yellow rust development in your crops. A few years ago, a week of sub-zero winter temperatures may have helped, but this is unlikely to be the case now.

“Furthermore, while we used to view yellow rust as a spring/early summer disease, it can now occur at any point during the season. For example, where it was commonplace for brown rust to take over from yellow rust as temperatures warmed up, yellow rust can now be found post flag leaf and on the glumes of wheat ears in a high risk season sporulating happily alongside brown rust.

“Therefore, it is essential that growers factor yellow rust control in to all spray programmes, starting early in the season, especially on those varieties that have dropped two points or more in terms of inherent resistance to the disease and those with resistance ratings of 5 or less,” he says.

Mr Bean says that of the 32 varieties on the AHDB Recommended List, seven have disease ratings that have dropped by two points or more. “While a one point drop would have been considered par for the course in previous years, a two point drop is very unusual and a three or more point fall represents a major breakdown in resistance.”

He points out that as a result of the more aggressive new strains, Spyder and RGT Conversion are now rated 6; JB Diego and Zulu 5, Britannia and Myriad have both dropped 4 points to 4 and the popular feed wheat Reflection is now rated just 3 for yellow rust resistance. “And from what we saw in both trials and the field, the fact that the long-time favourite, Claire only dropped one point to a 5 is something of a surprise.

“These wheats – particularly those where the ratings have dropped to 5 or below – will need closer attention, particularly if we get a season when yellow rust rears its head. Having seen what happened in 2016, we must also be very aware that with new races of rust appearing much more frequently than in the past, we can’t take anything for granted. The way that Zulu and Reflection broke down last spring, caught many of us by surprise.”

The good news though is that a decent Septoria control strategy should also control yellow rust and it need not cost the earth. “So, it is simply a case of getting the T0 timing right and then maintaining your guard through the T1 and T2 applications,” says Mr Bean.

While SDHI fungicides give a level of control, Zantra trials confirm they need back up from effective triazoles and strobilurins when the rust pressure is high at T1 or T2. “When Oakley was the dominant wheat variety, and its yellow rust resistance was on the wane, we found that adding a level of strob to the programme significantly improved control and yield performance and this is still the case today with newer wheat varieties.”

In Zantra variety trials in Shropshire last year – in what was a relatively benign Septoria season – the T0 gave a 0.66t/ha mean benefit across all wheats. However, in varieties such as Santiago and Reflection where yellow rust is a particular problem, failure to use a T0 resulted in a 1.8 and 1.2t/ha yield loss respectively, despite a belt and braces follow-up programme. Similarly, in Zantra’s trials in Kent, plots of Zulu that only had a T0 spray were clear of yellow rust compared to the virtually dead, 1.8t/ha lower yielding, untreated plots.

In Zantra replicated small plot trials, also in Shropshire, a triazole + chlorothalonil mix was a useful T0 base treatment providing a 0.3t/ha extra yield over chlorothalonil on its own. “This approach should be the starting point for 2017,” says Mr Bean. The benefit of a T0 in varieties such as Cordiale, Solstice and Zulu were very evident in farm situations where poorly timed applications, spray misses, or poor T0 product choice, led to yellow rust developing rapidly post T1 application.

Post T0, growers do need to take care that they then keep on top of follow-up spray timings. “An extended, 5 week gap between T1 and T2 last year meant that yellow rust escaped in poorly resistant varieties, compromising green leaf area and consequent yields.”

For the future, he points out that even though there are some good new varieties in the pipeline, many have Hereford in their parentage – including 7 of the newly recommended wheats. In continental Europe another new race of yellow rust which affects Hereford as variety has been isolated and so it will be important to monitor these newer varieties for signs of yellow rust infections. “Given the speed at which new races of yellow rust have been developing recently, extra vigilance is needed with all varieties” he says. “Nothing should be taken for granted”.

“Going forward, I firmly believe that the T0 will remain as a very important step in supporting a strong T1 and T2 programme that keeps the yield-building portion of the crop canopy going.”

Zantra has expanded its nationwide wheat variety, crop nutrition and fungicide trials programme to three regional sites in Kent, North Somerset and Shropshire and has a number of sites dedicated to replicated trials looking at a range of issues including fungicide development in various areas including Yorkshire and the Cotswolds. Growers interested in attending site visits or open days, should contact their local Zantra agronomist or ring the company’s technical support manager, Paul Beech on 07530 646078.

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