Employing an extended armoury of agronomic tools alongside the best available chemistry has become every bit as essential
Employing an extended armoury of agronomic tools alongside the best available chemistry has become every bit as essential in cost-effective septoria control in wheat as it is in tackling the scourge of black-grass, attendees to a research briefing heard recently.
Just like black-grass, wheat growers can no longer afford to rely solely on the ‘can’ to counter the country’s biggest cereal disease threat. Gone are the days when simple epoxiconazole and chlorothalonil programmes would deal with septoria tritici as effectively as Atlantis once controlled black-grass, said Agrii head of R&D, David Langton (left), speaking at a specialist research briefing.
The disease is far more difficult to manage these days with a growing range of strains showing far less susceptibility to even the most powerful azole fungicides, he commented.
“Thankfully, with multi-site protectants and SDHIs alongside azoles, we can still achieve good septoria control. However, we’ve reached the stage where we can no longer count on the level of fungicide ‘kick-back’ we used to. So, rather than eradicating infections, most of our focus has to be on preventing them taking hold in the first place. With the SDHIs that provide the biggest part of this activity known to be at particular risk of resistance development, we also need to do everything we can to safeguard them.”
Recognising this necessity, in recent years Agrii’s wheat disease research programme has been increasingly focused on integrated septoria management strategies incorporating a broad range of agronomic tools – including varietal resistance, drilling date and crop nutrition as well as fungicide timing, stacking and sequencing.
At the same time, Mr Langton and his R&D team have been exploring and developing a number of innovative approaches to improving fungicide choice and spray timing decision-making in several exciting national projects.
“Screening more than 2,000 lines with all the main breeders at our high septoria pressure iFarm in South Wales in the biggest programme of its kind in the country is identifying valuable sources of very much better resistance for UK development,” he explained.
“This is making a big contribution to increasing the number of varieties coming forward with septoria tritici resistance ratings of ‘7’ or more. Alongside it, ‘Co-ordinated Growing System’ (COGS) trials at our research sites across the country testing emerging new varieties to destruction well before their arrival on the Recommended List is providing growers with the most reliable local variety-specific agronomy advice.”
“Two years of trials at our AgriiFocus Technology Centre in Wiltshire have shown the crucial importance of variety selection and drilling date in septoria management,” added Agrii western region trials manager, Syed Shah (left).
“Even with a well-timed T0, septoria pressures in 2014 were so great that the disease proved almost impossible to control on all but the most resistant varieties sown in mid-September. And even with Crusoe – which we rate a 7 for septoria resistance – infections were only kept at bay with a robust fungicide programme.
“In contrast, untreated plots showed a dramatic reduction in infection levels across all varieties from late October sowing. Good septoria control proved possible here on varieties like KWS Santiago with a poor 5 resistance rating.
“Disease pressures were less last season, but we still saw responses of 2t/ha to the best fungicide programmes from Crusoe sown early and well over 1t/ha from later sowing,” he continued.
“This underlines the extent to which the right choice of variety and drilling date can take the pressure off chemistry,” stressed Dr Shah. “In seasons like 2012 and 2014, the wrong choices here could be very costly indeed. After all, the last thing anyone can afford is to spend a large amount on fungicides and still fail to keep on top of septoria.”
Crop health contribution
As well as variety and drilling date, three years of Agrii trials have revealed the substantial contribution improved crop health can make to wheat performance as part of the septoria management programme.
Yield responses ranging from 0.3-1.0t/ha have been recorded at AgriiFocus and other sites from a targeted and highly cost effective T0-T3 programme including quality formulations of foliar copper, zinc and boron. And encouraging results have been secured from the use of specific biostimulants, although the team insists far more work is required here to understand and validate the science.
“While our studies haven’t shown any significant reduction in septoria levels from the trace element programmes, the yield advantage they’re giving is clearly associated with greater green leaf retention,” Syed Shah pointed out. “So it looks like better nutrition is enabling the wheat to tolerate the disease better, helping to overcome the extra physiological stress it imposes. Interestingly, we’ve also been seeing clear varietal interactions in both our trace element and biostimulant trials suggesting their potential value in variety-specific agronomy.”
David Langton accepts that cost-effectiveness of fungicide chemistry to date has overshadowed the value of these other elements of agronomy in the septoria control equation. However, he is adamant that growing concerns over fungicide efficacy and resistance management – not to mention cost – are changing the balance of this equation markedly.
“We know that in most septoria situations these days we cannot afford to be without a T0,” he said. “Quite apart from the average 0.37t/ha response we’ve seen from this treatment in 17 years of trialling, the flexibility a T0 gives in both the intensity and timing of subsequent sprays is invaluable.
“Equally, it has become vital to use multisite protectants, stack and sequence triazoles and, in most cases, include SDHIs at both T1 and T2 for the septoria control we need these days in the face of changing fungicide sensitivity and greater climatic variability.
“So anything we can do to either reduce the pressure we put on the chemistry – in just the same way we’re trying to do with black-grass – or employ it more effectively through a better understanding of local weather, crop and disease conditions is becoming increasingly valuable.
“All the more so with control now so reliant on well-timed and largely protectant sprays,” he concluded.
Strategies to protect against septoria should include:
– Varietal resistance- Drilling date- Crop nutrition- Correct fungicide timing, stacking and sequencing