NEW yellow rust races coupled with widespread growing of wheat varieties with lower resistance ratings are putting Scottish crops at increased risk from the disease, growers are being warned, but a recently-launched SDHI fungicide could have arrived at an opportune time.

According to Syngenta Southern Scotland area manager, Iain Lindsay, Septoria tritici is a known threat with the wet Scottish climate, but yellow rust is much less predictable, and changes over the last few years have seen it increase.

“You pretty much know that you’re going to have to manage Septoria tritici so people correctly make this the starting point of their fungicide programmes," said Mr Linsday.

"Yellow rust can catch you out. Several catalysts over recent years have made it worse. For a start, new yellow rust strains have appeared. So, although you may start off growing a variety with good resistance, that can change.

“Also, the Scottish market is heavily geared to wanting soft distilling wheats, and some of the popular varieties have lower yellow rust resistance ratings. Because they are grown over a wide area, there’s little varietal diversity, so if yellow rust isn’t suitably managed, it can run like wildfire,” he added.

On top of these factors, Mr Lindsay said we haven’t had the cold winters we used to have, so overwinter development of the disease hasn’t been restrained.

“That said, we have had a harsher winter this season,” he pointed out, adding that that climate could help but even so, it's important not to be complacent.

“Geographically, crops in coastal areas are at greatest risk of yellow rust, due to the damp air. The problem can be found in counties stretching from Northumberland up to Fife.”

Independent plant disease expert, Prof Fiona Burnett of SRUC, agrees that yellow rust has been common in the last couple of seasons, and says yellow rust can even extend further north.

“In the last two years we’ve seen quite a bit in Aberdeenshire,” notes Prof Burnett. “It cycles faster than Septoria tritici.”

When it comes to management, Iain Lindsay suggests control needn’t be expensive, but it is important to ensure that fungicides used against Septoria are also strong against yellow rust – and to get on top of over-wintered infection early, for example with a suitable T0 fungicide, and then to maintain a preventative approach.

“You can control it cost-effectively by tailoring the fungicide dose to the variety,” explained Mr Lindsay. “But I’d say with any disease, prevention is better than cure.

“If you are concerned about yellow rust, build it into your fungicide programme. Results on the new SDHI-based fungicide, Elatus Era (solatenol + prothioconazole), from its launch year last season have backed-up previous findings – showing that Elatus Era was as good or better than similar treatments tested against Septoria, and superior against yellow rust.

“In addition, independent AHDB fungicide dose curves have backed-up its strong yields in trials. In a Scottish situation, applying Elatus Era at T2 as part of the programme, rather than T1, is probably the better option, because you want to use its strengths to help crops hold on to green leaf area for the best benefit for yield. Maintaining green leaf area near the end of the season can increase yield by 0.15 t/ha/day, so an extra three days can be worth an extra £60-£70/ha.”

Prof Burnett also has had an experience of Elatus Era in trials, and welcomes the fact it is a pre-formulated SDHI + azole mix. “I’m a fan of pre-mixtures, of which Elatus Era is one. It is among the best of the newer SDHI-based mixture products. The fact it contains prothioconazole gives an opportunity to mix and match different azoles through the programme. If you use one azole at one time and another at another time, it makes it harder for Septoria tritici to adapt.”