With wheat's most critical disease control timing looming, what is the advice for growers in a year with wildly differing drilling dates and crop development, the arrival of new chemistry, and relatively low spring disease pressure? Martin Rickatson reports.
Low early season septoria pressure this year has been tempered by hugely variable wheat crop development which has made some think twice about product, timing and even whether to apply an early spray.
To throw a further curveball into the mix, rising wheat prices mean some are now reassessing for T2 the cut back investment fungicide investment plans originally made for crops considered from the off to have low potential. But with flag leaf spray time approaching rapidly, how should the spread of drilling dates and growth stages be tackled?
In the West
Shropshire independent agronomist Dale Hardgrave points out the enforced wide drilling window has made accurate timings tricky all the way through fungicide programmes to date and T2 is unlikely to differ.
He says: "At T0 and T1 - where in many cases we chose to cut back on inputs due to low disease pressure and reduced crop potential and sometimes didn't apply a T0 at all - every field required close examination to identify individual crop stages, with earlier-drilled crops in some cases being as challenging as later ones," he says.
"Crop progress has been as much about soil type and topography as drilling date and by mid-April, with lack of rain leaving little surface moisture to help them pick up fertiliser, many wheats weren't looking great, regardless of when they were sown. While some catching up may occur, there's likely to be a knock-on effect in terms of varied flag leaf emergence, requiring prioritisation based on assessing the trade-off between crop potential and disease risk factors.
"However, one upside of the drier spring has been relatively low disease pressure. Yellow rust pressure is actually higher this spring than usual here in the West, while septoria pressure is lower. By T2, though, pressure levels may change and, as the most important disease management timing, it isn't the one at which to be cutting costs.
"That said, it may not be the year to make big investments in new chemistry either. We're likely to try some Revystar XE as it looks to offer a significant advantage over Ascra Xpro, although that judgement is obviously based only on impressions from trials given it's not yet been used widely on a commercial basis. However, few crops this year would appear to have the potential to justify broad investment in the significantly higher product cost."
In the East Midlands
Nottinghamshire-based Peter Brumpton, AICC agronomist with Arable Alliance, believes that while winter wheats in the East Midlands - subject to some of the worst of last year's rainfall - span a huge range of establishment dates, by T2 their development disparity should largely have evened out.
"Within reason, by flag leaf emergence the difference between many crops is likely to have narrowed, and by this stage in the season's fungicide programme things shouldn't be that much different from a ‘normal' year, provided there are no significant weather events," says Mr Brumpton.
"Focus firstly on the most advanced crops and those appearing to have the highest potential, plus those which have been subject to the longest gap since T1 - when stocks of chlorothalonil should ideally have been used up, as many T2 applications further north are likely to be made after the last legal date of May 20."
With wheat growers now having new chemistry available to them, T2 provides the best opportunity to trial its abilities on certain fields, says Mr Brumpton.
"As disease pressure in spring was relatively low, wholesale use at T2 is unlikely to be justifiable, but new technology is worth testing, and investment in the additional costs of new chemistry is best targeted at T2 on those crops with greatest potential where it will give the greatest return."
While septoria remains a concern given its typical continued presence on lower leaves, the dry conditions during early spring mean pressure has been relatively low. However, notes Mr Brumpton, yellow rust's continued adaptation to its environment is arguably of greater importance at this point.
"As long it's monitored, though, and addressed if it develops in the run-up to T2 and beyond, it shouldn't become a big issue."
In the North
Even in northern England, where lower black-grass pressure allows for earlier drilling, the wet weather meant winter wheat was drilled over a wide date range, and much less was sown early, says Nigel Scott, Durham-based northern technical manager for ProCam.
He says: "Development speed is about variety as much as drilling date, with the likes of Extase and Firefly being faster early developers than types like Graham, and there was a vast difference of as much as 10 days in crops at T1. By mid-April, some mid-September-drilled crops were showing leaf 3, while later ones were still mid-tillering.
"While crop stage difference will have narrowed by T2, both drilling date and variety will still have an effect on development stage, and when added to disease pressure and varietal susceptibility, this should influence prioritisation.
"Although the dry spring minimised disease pressure, it's not long since things were very wet, and septoria inoculum which developed in the base of the crop then could still splash up onto higher leaves if we get significant rain events. Despite the variety's high rating, it's visible even in Extase - although largely in crops that probably shouldn't have been drilled so early.
"While reduced yield prospects from the poor start to the season and low disease pressure may have tempted some growers to restrain their spending, rising wheat prices should perhaps encourage them to think again, particularly at T2, where yield response to fungicides is greatest. In 2018, our trials produced a 0.8-0.9 tonnes per hectare response to fungicides, but last year, when it was dry through to June, that jumped to 5t/ha. Low early disease pressure shouldn't make growers complacent.
"Crop potential and disease conditions may not be encouraging significant investment, but higher wheat prices and predicted shortfalls in production perhaps should be. Spending an extra £12/ha to ensure the crop and get the maximum from it could be well worthwhile.
"There may be a T2 place for Revystar in high pressure septoria situations, but don't forget also the value of products from chemical groups other than azoles and the benefits the physiological effects SDHIs and strobilurins can bring about. Over the past two seasons we've run a trial assessing the value of two SDHIs in a programme versus one. While the 2018 growing season started wet and ended dry, the opposite was true last year, leading to different disease pressure levels. However, using two SDHIs gave a 0.6t/ha yield benefit in both years.
"And in wheats in areas of the country where T2 falls within the cut-off date for last applications, there is a final chance to use up chlorothalonil on the flag leaf. It's also worth considering the opportunity to boost backward crops via tank-mixed micronutrients and biostimulants to counter late season stress. Supplementary magnesium and, particularly if dry, potassium, can arrest chlorosis caused by deficiency."
Continue to protect lower leaves
Iain Hamilton, Syngenta technical manager, suggests that, in backward crops, a secondary aim of T2, alongside protecting the flag leaf, should be extending protection of the lower leaves.
He says: "With the winter having been mild as well as wet, septoria developed in the base of many wheats, especially in those drilled pre-Christmas, but those lower leaves will play more of a part in yield-building than usual in backward, open crops."
Syngenta trials work shows coarser spray patterns at higher water volumes achieve the best crop penetration at T2, with 75% reduction nozzles advised at T1 and T2 at either 100 or 200 litres/hectare of water in normal conditions, and 90% drift reduction nozzles and a minimum of 200 litres/ha of water in more challenging ones. At T2, for every day disease control is delayed, wheat yield can decline by 70kg/ha, suggesting nozzle and water rate can make more spraying days available.
"Where expenditure was cut back early or timings were missed, there may be consequences later," warns Mr Hamilton.
"The thought process behind cutting back investment for a crop which appears to have low potential is a self-fulfilling prophecy. Work to a rate rather than a cost, and don't be complacent.
"Much will also depend on what was applied at T0 and T1, and on spraying capacity and how quickly it's possible to get around a farm's fields and varieties as flag leaves emerge. Different businesses have different levels of risk aversion and different areas to cover. And earlier timings which were missed because of the speed of crop development or perceived low disease risk may have an impact down the line - events such as last June's rainfall after T2 show the dangers.
"As the weather can't be predicted and there is more protective activity than curative from currently available chemistry, it's best to be insured. Protection, persistency and timing will be important.
"Adapt to individual situations by variety, location, weather and risk aversion policy. Situations which get out of hand can't be rescued, even with new chemistry, and protection is still easier - and cheaper - than cure. And remember, multisites remain important, particularly for septoria management. Consider CTL use at a T1.5 timing - leaf 2 emerged - if GS39 will be after May 20."
