Crop Doctor – Septoria low at T2

 

As flag leaves begin to emerge across the country, Crop Doctor travels from west to east to assess disease progression or the lack of it. CPM joins the experts to explore the implications of the cool, wet May on fungicide programmes.

The potential ‘googly’ this season may be grain fill due to later than normal ear emergence.

By Lucy de la Pasture

Farming folklore suggests a cold, wet May brings a barnful of hay (or grain) and it certainly was cooler than average and, in contrast to April, it was much wetter than the norm. On 25 and 26 May, the Bayer ‘Crop Doctor’ team made a slightly abbreviated tour across regions to find out how wheat varieties were looking and how the continued unseasonal weather was affecting disease development.

Cold at Callow

A cold north-westerly was blowing across the slopes at Bayer’s Callow trial site in Herefordshire. With ADAS’s Jonathan Blake, local AICC agronomist David Lines and Bayer’s commercial technical manager (CTM) Gareth Bubb wrapped up in clothing more suited to a winter’s day, it’s fair to say the plots look well, in spite of the weather.

“Having had just 22mm of rain in March and a further 21mm in April, we’ve already had 120mm at Callow this month,” explains Gareth.

A month ago the experts were predicting the universally backward wheat crops would race through their growth stages and the flag leaf would come out as it normally does, on around the 20 May. It was anticipated that this would make the gap between T1 and T2 fungicide applications closer together than usual but what’s actually happened is the complete opposite, he explains.

“The T1 was applied here over four weeks ago and, in some varieties, full flag leaf emergence is still a week away – meaning that the gap between the two main fungicide timings is extended and will be up to five weeks apart,” says Gareth.

David has been seeing the same thing in commercial crops, with the flag leaf emerging over a very protracted period. “Leaf one was starting to emerge a fortnight ago and in some fields is still only 60% emerged. That means some of the leaf has been exposed for three weeks before the T2 spray is applied.”

The differences between the varieties in their spring growth is stark at Callow, with forward-looking KWS Extase proudly displaying its flag leaf and KWS Barrel at the other end of the spectrum, having just reached GS37 with final leaf two 10-30% emerged.

The dry April prompted many discussions about T1 fungicide applications, given the very low levels of disease visible in the crop and absence of latent septoria in qPCR tests on the newest leaf layers.

Jonathan spots some septoria lesions on the tips of leaf three in untreated KWS Barrel, giving him cause for concern that septoria could come back and bite growers who have skimped on early protection. Even so, the results of the Rapid Disease Diagnostic (RDD) testing at Callow are still reporting surprisingly low levels of septoria, even in the untreated plots, and after wet conditions which you may think would have favoured the disease.

Yellow rust is much more easily found, says Jonathan. It’s just beginning to show up in a number of varieties at the Herefordshire site, with the untreated KWS Kinetic looking the worst by far. Brown rust has also been notable by its absence, even on the most susceptible varieties.

“Brown rust is just beginning to appear on Crusoe, which is much later than normal and reflects the season we’ve had so far. April and May have been cool and brown rust development is favoured by warm conditions.”

David is of the view that as soon as the flag leaf is fully emerged, the T2 fungicide should go on. His programmes will be tailored to varieties and situations but will be based around Ascra xPro (bixafen+ fluopyram+ prothioconazole) or Univoq (fenpicoxamid+ prothioconazole).

“The differences between varieties this spring means that getting the timing right for each one is important. If you go too early then not all of the flag leaf will be protected and it may mean a stronger product will be required at T3 to top up the protection.”

Gareth believes there may be a temptation for some to merge the T2 and T3, which he doesn’t believe is a good idea on two counts. “Most crops have already had a five-week gap between fungicides so it would be a mistake to combine the T2 and T3 and compromise the optimum timing for them both. It still makes sense to apply the T3 separately, even if the timing occurs just 10 days after the flag leaf spray goes on.”

In his view, there’s a case for using an SDHI at T3 if only one has been used earlier in the season. This could be driven by an increase in disease risk due to weather or by a compromised earlier spray. He points out the SDHI component boosts septoria and brown rust activity and if using Aviator (bixafen+ prothioconazole), there’s no compromise in fusarium control either.

Jonathan notes that the stem-based browning that was beginning to show in the KWS Extase plots a month ago has continued to develop, with some penetrating eyespot lesions and signs of nodal fusarium infection.

“May has been good weather for stem-based diseases, particularly eyespot which is more prevalent than we’ve seen for a long time.”

In his view the stem nodal and internodal fusarium levels currently visible in Extase, but also evident in some of the other varieties in the demo, means growers should watch out at T3 – the optimum fungicide timing to protect the ear from developing the disease. “The humidity from damp soils and presence of the pathogen on the stems gives a higher chance of fusarium infections on the ear,” he says.

David adds that where crops have had prothioconazole at T1 and T2, it should have reduced fusarium levels.

“But T3 is the critical timing,” highlights Jonathan. “If there’s any fusarium inoculum present and conditions are conducive then the evidence suggests you’ll get fusarium on the ear. I wouldn’t ignore it in a season where varieties appear to have current infection.”

Optimism at Long Sutton

David Hoyles, who hosts the Bayer demonstration site at Long Sutton in South Lincolnshire, says winter wheat crops look to have a lot of potential after 83mm of rain during May, which averaged 9⁰C.

“Crops have come on a lot in the past month and have caught up a bit. Most are now 7-10 days behind normal in terms of their development, compared with the 10-14 days they were behind at the end of April. Jonathan described the demo plots as ‘open’ on his last visit, but we’ve looked after them this month – paying particular attention to micronutrition – so we’ve held on to a lot of tillers and plants have filled out.”

As always, much now depends on the weather during the crucial months of grain fill. “We don’t want another 2012 as low levels of sunlight will produce grains with low specific weight in the better crops on this ground. If June sees temperatures of 20⁰C and if it’s bright and sunny, then the potential of crops is above average this year,” says David.

Jonathan agrees that in many ways the odd spring has worked in the crop’s favour, with low levels of disease, a slowly developing canopy and enough soil moisture to ensure nitrogen uptake. “But the potential ‘googly’ this season may be grain fill due to later than normal ear emergence,” he says.

“September/October sowings this year have had their grainfilling pushed back 7-10 days by the cold spring. They’re now more akin to a November or December sown crop, which on average would have a lower yield due to grainfill period happening later than the optimal period for light capture.”

On the whole, the cold dry northerly winds which have predominated during May have kept disease at bay. Bayer’s James Wilkins says that significant yellow rust has started to creep into untreated KWS Zyatt during the past week (last week of May), with high levels also visible in KWS Kinetic and Skyfall.

Jonathan says he was expecting yellow rust to be much worse at Long Sutton and speculates that the relatively cold May is the reason why it hasn’t taken off. David agrees, adding that there were 15 frosts during April and even some late frosts in May, when temperatures have barely reached 15⁰C during the entire month.

A T1 fungicide was applied to the plots on 30 April, which look generally clean, with a T2 planned for 27 May, says James. “Growth stages are very variable between different varieties so there’s likely to be a long tail to T2 applications this season, which is unusual because generally there’s a concertina effect and varieties are ready to spray at a similar time.”

David says it’s the same in his commercial crops and he reckons there will be at least a week difference in T2 application dates if they’re timed for when the flag leaf is fully emerged. He’s also noticed that drilling date isn’t necessarily a guide to spraying order, with LG Astronomer and LG Prince currently at 70% flag leaf emergence which is behind some varieties which were drilled later.

David is planning to base his T2 fungicide programmes around either Ascra or Revystar (fluxapyroxad+ mefentrifluconazole). He’s finding the results of the rapid disease testing fascinating and it’s helping him pare back product rates.

“If I hadn’t had the information that there was no latent septoria on the top leaf layers then I would have maintained a higher dose of fungicide at T2 this spring. But in light of the disease testing I’ll be cutting back rates according to risk, based on crop density and variety susceptibility, knowing that we’re in a protectant scenario. That has to be good for sustainability,” he says.

There’s an interesting conversation around T3 at Long Sutton, particularly as Jonathan has also spotted nodal fusarium bubbling away in some varieties, as it was at the Callow site. David asks him how he can best target fusarium in crops this season given the variation in growth stages, particularly between ear emergence on the main stem and crops with many tillers.

“The ideal timing for fusarium is early to mid-flowering. The variations in growth stage we’re seeing are likely to continue, so timing T3 is likely to be trickier than normal,” says Jonathan.

He highlights that T3 sprays are around 50% effective, on average, but suggests this could be improved by splitting the application and applying two reduced doses, four to five days apart. It’s not a theory that Jonathan has found growers keen to try out but that may change as David’s eyes lit up at the prospect – late season disease can be a particular problem on his farm, he notes.

qPCR reveals distinct lack of septoria

 

Although it’s only been thrust into the limelight this season, Bayer is now into its eighth year of qPCR testing for septoria and yellow rust. This season alone, 80,000 leaves will be tested across five different countries, providing a big picture for disease development, explains Bayer’s Rosalind Martin.

 

“Rapid disease diagnostics provides another layer of information to help support decision making and is a tool we’ll continue to offer to growers over the next few seasons.”

 

Bayer takes samples from sites across the country to give a national snapshot of disease development, with monthly sampling in January and February increasing to weekly for the rest of the growing season. The latest May snapshot provides information on latent disease present on the top four leaf-layers.

 

“Surprisingly there’s no latent septoria present across the country in leaves two to four but this reflects the cold weather. Most regions haven’t reached 15⁰C, which is critical to push septoria through its latent phase so it can become problematic in the upper leaf layers,” she explains.

 

Bayer’s Ben Giles has been monitoring two sites this season – one at the Hinton Waldrist demo site in Oxfordshire and the other at Russell McKenzie’s farm in Cambridgeshire.

 

“At the moment (last week of May) disease levels are very low in the untreated plots, with septoria only detected on leaf five. At Hinton, there’s been 110mm of rain in the past calendar month, but the temperature has only reached 15⁰C once and that has prevented septoria from ‘kicking-off’,” he explains.

 

“A lot of growers cut back at the T1 timing and Ascra rates were shaved to 0.8 l/ha, which would have been a worry if it were warmer. As it is, we can be confident that even though the fungicide interval between T1 and T2 is being stretched, we’re still in a protectant situation.

 

“Even where septoria is present in the bottom of crops, the chances of it getting to the leaves in the upper canopy in one cycle of the disease are very low. That means we can feel relaxed about the gap this spring.”