Despite recent dry, cool conditions and well-timed T0 and T1 sprays in winter cereals, key diseases such as septoria and rhynchosporium remain a threat to wheat and barley crops.

With the lack of frosts adding further pressure, even the hardiest barley varieties, are showing signs of rhynchosporium at the SRUC’s Bush and Cauldshiel sites.
 
The big worry now, according to agronomists attending last week’s CropDoctor North meeting, is that a return to wet and humid conditions will kick start disease again.
 
Agrii agronomist, Greig Baird, said he will be looking at robust prothioconazole mixtures with strob and CTL at the T2 timing, in such situations and will also consider an SDHI where disease pressure is high or potential warrants it. 
 
“Many growers have already applied an SDHI but where the disease pressure is high or crop potential is promising, I would consider a second SDHI. At this moment some of these crops have the potential for 10t/ha – it all depends on the weather.”
 
The good news is mildew, net blotch and rust has all but dried up in crops. But the situation with septoria in wheat is broadly similar to that of rhynchosporium. Disease is still present in the lower leaves and untreated plots have high levels, with some of the more resistant varieties showing plenty of the disease.
 
“The cool spell has checked disease but also plant growth. If we get favourable weather now the disease hasn’t got far to go to get into the upper canopy. 
 
“At the T1 timing another 2014 looked possible. The pressure has slipped back, but as temperatures rise and plants ‘gain ground’ there is an increased risk of the disease spreading up the canopy via rainsplash or leaf rubbing. A few rain events could get easily it going again,” he said
SRUC’s Dr Fiona Burnett said there can be no compromise with T2 applications, regardless of T0 and T1 sprays. “What growers cannot
compromise on is T2 timing or product choice. In some situations, we have seen growers forced into applying T1s a little early and the danger is that any extended delay to T2 sprays will allow septoria to become established. 
 
“Full protection of the flag leaf is essential and growers need to adhere to the GS39 timing – full emergence of the flag leaf – even if the gap from T1 is short. As much as 60% of your yield response can come from this timing.”
 
She also pointed out that the 80% dose recommendation for azole/SDHI co-forms is just that – a recommendation. 
 
“Where growers are concerned that the gap could be stretched, a higher dose may be welcome to provide the greatest ‘kick back,” she adds.
 
Yellow rust was also still visible on some the more commercial crops and Dr Burnett advised growers to think ‘disease spectrum’. 
 
“I have received reports of eyespot in some areas – perhaps not surprising given our propensity for early drilling, coupled with the warm autumn and min-till cultivations. Ideally, the T1 is the best control opportunity but some growers might need to factor it in for flag leaf sprays,”
she noted. 
 
However, she added there is much uncertainty regarding the latest yellow rust outbreak in Aberdeenshire and that adult plant resistance could kick in.
 
Instead, Mr Baird said a good septoria programme should manage the disease spectrum. 
 
“We’re having to front-load programmes because of milder winters but this is helping us stay in a protective situation. Azoles have largely lost their curative septoria properties but are still good protectants across the disease spectrum when used at robust rates. 
 
"I’m seeing some stem-based disease, especially eyespot in the prone areas, such as East Lothian and will need to be incorporate this in to T2 sprays where maximum plant coverage will be essential.”
 
His T2 sprays are likely to be based on BoogieXpro or Brutus + Imtrex but a strob might be added to provide some additional kick-back against yellow rust. The decision to go prothioconazole or epoxiconazole is driven by T1 azole choice but he acknowledges that spiroxamine in
BoogieXpro does make it a very good Septoria + yellow rust choice. Yellow rust he said, is not causing too much concern, but he recognises its ‘visualness’ can be impactful. 
 
“It does cycle faster than most diseases and if it gets in it can look dramatic. That is why the gap between sprays is so important.”
 
For SDHI T2 rates Mr Baird is keen to see rates maintained. “The SDHIs are the only curative septoria active we have. If we lose them, there would be no way of eradicating any established infection. It begs the question about how many sprays might be needed to keep the disease out if we saw a repeat of 2012 or 2014 in the future.”
 
Bayer’s Neil Thomson also worries about timing and added that many varieties favoured in Scotland have poor ratings against septoria. 
 
“Most of the soft feed wheats get a five against the disease which means that growers can’t use varietal resistance to buy a bit of time with applications.”
 
As a result, he prefers Xpro fungicides held back for that all-important T2 timing. “One of benefits of the Leafshield formulation in products such as Aviator235Xpro is its leaf adhesion. Research with the Silsoe Spray Applications Unit has shown that on dry leaves, Leafshield formulated fungicides are dried within a minute in most situations. That is a big comfort if catchy conditions are forecast.”
 
Looking at spring barley, plots had established well in both areas but many commercial crops were in a different situation. 
 
With early drilled crops going into poor seedbeds, many had suffered with the result, tillers could be reduced, and growers may be tempted into ‘cheap 'n' cheerful’ T1s as a result. 
 
Dr Burnett warned: “That could pose a risk of disease getting established, prompting a potential increase in T2 spend. I would rather growers adopt a risk management approach and protect crops accordingly. That doesn’t necessarily mean moving to an SDHI but just sticking with robust rates of prothioconazole mixes,” she cautioned.
 
Mr Baird will consider SDHIs at the T1 timing in an attempt to help boost tiller numbers. “Azole + strob + CTL will give you good disease control but doesn’t offer the same physiological boost as an SDHI.”
 
A good establishment at Bush and Cauldshiel meant that spring crops were showing few signs of disease but all warned against the potential threat of ramularia. 
 
Dr Burnett did however remind growers that most varieties have ‘tolerance’ rather than ‘resistance’ and the disease is often ‘under the radar’.
“It’s a disease that comes from all angles – seed borne, trash, transfer from winter barley. That’s why best practice is so important.”
 
It’s also another reason to avoid ‘cheap n cheerful’ T1s, she said, pointing out that a severe outbreak could take around 1.0t/ha off a spring crop and impair grain quality.