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Fungicide mixtures key to maintaining disease control

Performance of plant protection products and getting the most out of barley was the focus of the HGCA Agronomists’ Conference

The performance of plant protection products as well as advice for getting the most out of barley was the focus of the morning session of the HGCA Agronomists’ Conference, staged at the East of England Showground prior to the Christmas break. Dominic Kilburn reports on some of the detail.High disease pressure in 2014 has provided researchers with good fungicide protectant and eradicant data for septoria, and other diseases, in trials across seven different sites in the UK and Ireland. And, kicking off a number of technical presentations at the HGCA Agronomists’ conference was NIAB director of crops and agronomy, Stuart Knight, (left) who summarised findings from NIAB TAG, ADAS and SRUC research funded by HGCA and from TEAGASC in Ireland.Protectant activity
Referring to septoria protectant trials, Mr Knight began by highlighting that Bravo (chlorothalonil) was still doing a very good job of protecting wheat crops, out-performing the azole standard Ignite (epoxiconazole) under high disease pressure in Hereford.Straight SDHI fungicides in the trial included Imtrex (fluxapyroxad) and Vertisan (penthiopyrad), which provided improved protection over Bravo and Ignite, although delegates were reminded that straight SDHIs should only be used in a mixture with at least one fungicide with an alternative mode of action and effective against the target disease. “SDHIs should always be applied in a mix but here we were testing them as straights to evaluate their strengths and weaknesses,” Mr Knight pointed out.
SDHI/azole mixtures of Aviator (bixafen + prothioconazole), Adexar (fluxapyroxad + epoxiconazole) and Vertisan + Ignite were all very close in terms of their performance levels, he added.
Looking at the mean of six septoria protectant trials in 2014, according to Mr Knight, multisite product Phoenix (folpet) gave reasonable protection but it was not as effective as chlorothalonil. Solo SDHIs Imtrex and Vertisan gave improved protection, as did the SDHI mixtures. “Proline (prothioconazole) showed an advantage over Ignite in 2014 in terms of protectant activity but this has varied from year to year. The differences are likely to be seasonal effects rather than relative shifts in sensitivity,” he commented.When considering over-year data (2012-2014) Mr Knight highlighted that the azoles Proline and Ignite were more closely matched, but were not up to the solo SDHIs or SDHI/azole mixtures’ level of performance, the latter two groups all performing relatively closely.Septoria eradicant
Turning to trials looking at septoria eradicant performance (four trial mean in 2014) there was no difference in performance between the two azoles Proline and Ignite, however SDHI solo products Imtrex and Vertisan were again more effective than the azoles and the three closely-matched SDHI/azole mixtures were better still.Where a fourth SDHI fungicide Seguris (isopyrazam + epoxiconazole) was included (in over-year 2012-2014), it was weaker in a septoria eradicant situation compared with the other three SDHI mixtures mentioned above, but its performance as a protectant was comparable to the others.Confirming that 2014 was a good year for fungicide performance data, Mr Knight said that as much as a 4t/ha yield response over untreated had been seen in the wheat trials this year from a single spray, adding however that, as not representative of multi-spray programmes, yield differences should be treated with “caution”.Yields across all seven 2014 trials demonstrated that solo SDHI Imtrex out yielded Vertisan, while azole Proline yielded higher than Ignite due to its better protectant activity in 2014.
“There was a good performance from chlorothalonil – better than the azoles – but not as good as the solo SDHIs.”SDHI/azole mixture Vertisan + Ignite did not match Aviator or Adexar for yield in 2014,” he added, “despite achieving the same level of septoria control.”Wheat rust trials
The brown rust trial (Cambridge 2014), which was inoculated with the disease to ensure an adequate level, offered a good test of products, said Mr Knight, with good control from Imtrex and Vertisan, however strobilurin Comet (pyraclostrobin) was the star performer against brown rust with very strong control, he suggested.”The same SDHI mixtures did well, however Aviator was slightly off the pace from the other three, probably because it contains prothioconazole, while the others have epoxiconazole in their mixtures.”
Referring to yellow rust trials, he said that Ignite offered very good control, with good control also from Comet, while others including Imtrex and Vertisan all contributed. As with brown rust, Aviator offered less control than Adexar, Vertisan + Ignite and Seguris SDHI mixtures.With the mixtures more robust on rusts, across wheat yield and disease, overall they clearly had an advantage over solo SDHI products.Barley performance
Barley fungicide trials in 2014, for example at Lanark, demonstrated good protectant activity still from Proline against rhynchosporium, with Imtrex outperforming Zulu (isopyrazam) when comparing the solo SDHIs, continued Mr Knight.Of the SDHI mixtures Siltra Xpro (bixafen + prothioconazole) and Adexar offered the best protection against rhynchosporium and were closely matched. Vertisan + Proline was slightly “off the pace”, giving less improvement over Proline on its own.Over the 2012-2014 period for rhynchosporium protectant activity; Zulu didn’t perform to the level of Proline or Imtrex while the three SDHI mixtures (Siltra Xpro, Adexar and Vertisan + Proline) provided very good and evenly matched control.In an eradicant situation for the same disease in 2014, for example at Cardigan, Imtrex was again better than Zulu, while Vertisan + Proline provided less control than the other two SDHI mixtures. “But when comparing SDHI mixtures over the 2012-2014 period all have performed well,” added Mr Knight, confirming that multisite product Phoenix was ineffective against rhynchosporium in 2014 but had shown limited activity previously.In 2014 net blotch trials at High Mowthorpe, protectant activity of the solo SDHIs Imtrex, Zulu and Vertisan was as good as, or better than Proline, and while Comet was still showing “useful activity”, it was not as good as the solo SDHIs or Proline.All the SDHI mixtures were as good as or better than the solo SDHIs, and results for eradicant activity at the same location were similar, with Imtrex performing slightly better than the other solos, added Mr Knight.Over-year (2012 and 2014) analysis of net blotch eradication included SDHI mixture Bontima (isopyrazam + cyprodinil) and, although the product doesn’t contain an azole, it matched the other SDHIs mixtures in terms of performance, he noted.A brown rust trial in barley (Caythorpe 2014) demonstrated that Imtrex, Zulu and Comet all gave very good levels of control, as did the mixtures Siltra Xpro, Adexar and Vertisan + Proline.To conclude Mr Knight pointed out that, when considering yield results from the barley brown rust trial, the SDHI/azole mixtures had (in 2014) delivered up to a 0.5t/ha yield advantage over the solo products Imtrex, Zulu, Comet and Proline.”In addition, brackling data from the 2014 trial showed that all products gave a good reduction confirming that they can provide more than disease control and yield increases.”Maintaining control
Pesticide regulation and resistance issues with wheat fungicides are a potential ‘car crash’ waiting to happen and avoiding action needs to be taken, stressed ADAS head of crop protection, Dr Neil Paveley, who posed the question as to whether wheat crops should be treated in a similar way to potatoes to maintain the required level of disease control. “The number of fungicide applications is increasing and the question is whether we should continue that trend and end up treating every 7-10 days as we do against potato blight?”Dr Paveley explained that, according to the Defra winter wheat disease survey, both the number of spring fungicide timings in wheat, and the percentage of crops treated at each timing, had increased significantly since the early 1990s, despite the fact that, although disease pressure has varied greatly from year to year since, the overall septoria pressure had not increased.He pointed out that back then, a standard triazole such as propiconazole, at half dose, gave useful activity against septoria while a full dose provided similar disease control effects comparable with SDHI fungicides today.”T1 and T2 timings were driven by the understanding that we could get protection or eradication over the full extent of the upper leaves, and that remains true now. But threats such as the yellow rust Warrior race made the gap between T1 and T2 seem longer, while legislative reasons for T3 protection against mycotoxins have combined to drive the number of treatments up.”The consequence of this is that a higher number of treatments are now applied, which has led to a decline in product performance,” he added.According to Dr Paveley, although the decline in performance of azoles has been obvious for some time, new strains of septoria pathogen are likely to have resistance to SDHI and most single-site fungicides at some point in the future, albeit not immediately. “We get new broad-spectrum fungicide chemistry about every 20 years and it will probably be several more years before we see another broad-spectrum mode of action, and even then it’s got to get through the regulatory authorities.
“New septoria strains will overcome SDHIs eventually but for the moment we have to look after what we’ve got,” he added. Dr Paveley listed the options for increasing the robustness of fungicide programmes with current chemistry: increasing dose rates, increasing the number of spray timings, splitting dose rates, and adding in different chemistry as a mixing partner in the programme.However, presenting data from a global study of the consequences of these courses of action on fungicide resistance, he pointed out that adding in a mixture partner to the programme with a different mode of action, was found to be the only option that decreased resistance selection pressure substantially, while the others all led to a significant increase.”It’s clear that treatment decisions determine fungicide resistance and so the advice to growers should be to build mixture products in from the start; maximising the use of multisite products throughout the spray programme and limiting the number of azole treatments where possible.”Azole efficacy is worth maintaining for their own contribution to disease control as well as helping to protect SDHIs and they should be used robustly at T1 and T2, when mixing with SDHIs, but alternatives to azoles should be considered when targeting septoria or rusts at T0 or T1.5.”Varietal resistance
Disease resistance in varieties should also be considered as another ‘mode of action’, commented Dr Paveley and, despite the fact that the most resistant of the RL varieties tended to be towards the lower end of the yield spectrum, this shouldn’t put off growers selecting them.Research in 2014 demonstrated that when comparing the more disease resistant varieties across low and moderate fungicide programmes, with higher input programmes on less resistant but higher yielding varieties, gross margins were very similar.”While this was taken from one year’s data, and so should be treated with caution, it’s clear that variety resistance makes the overall intensity of the spray programme less critical,” he added.
So should we treat wheat like potatoes, with multiple sprays? “No,” he concluded. “Because if we use more sprays against septoria, our fungicides will stop working and we will apply more to achieve less.”More from barley
‘Getting the most out of barley’ was the title of a presentation made by ADAS head of crop physiology and principal scientist, Pete Berry (left).He began by saying that although average on-farm winter and spring barley yields had risen over the years (winter 6.6t/ha and spring 5.5t/ha), there was potential to raise yields further.”The record for a crop of winter barley stands at 12.2t/ha and trial yields regularly achieve 12t/ha for winter barley and 10t/ha for spring,” said Dr Berry, who pointed out that feed winter barley yields in Recommended List trials yield the same as second wheats but cost 146/ha less in terms of inputs (Nix).An HGCA review of 25 nitrogen timing experiments, with participation by Syngenta, GrowHow and ADAS, demonstrated that a 0.5t/ha yield increase can be achieved from applying more than 50 per cent of the nitrogen programme before stem extension (GS30) compared with less than 30 per cent being applied earlier.”The mechanism for the improvement in yield is brought about by maximising light interception within the crop – the more light that can be intercepted then the increase in the number of grains per m2,” commented Dr Berry.Other implications of earlier nitrogen applications included a reduction in grain N by 0.1 per cent and an increase in crop height by as much as 10cm, he pointed out, adding that there would be a likely increase in lodging risk.In addition, Dr Berry said that research work looking at optimum nitrogen rates concluded that winter barley crops with a yield potential greater than 8t/ha require more nitrogen input than that recommended by RB209.”The higher the potential of the crop, the optimum N rate also increases and an additional 27kg/ha is required for each tonne above 8t/ha,” he suggested. However, when increasing N rates growers need to be careful to consider implications on grain N content and to comply with NVZ regulations.”Lodging issues
According to Dr Berry, 76 per cent of winter barley grown in the UK receives a PGR treatment, half of which is chlormequat, which only has a small effect on shortening the crop, and shouldn’t be relied upon to reduce moderate or high lodging risks, he noted. “But other gibberellic acid inhibitor actives and Ethephon (2-chloroethylphosphonic acid)-containing products can shorten barley by as much as 8-10cm, with the greatest shortening taking place when applied after GS37.”Only 18 per cent of the spring barley area receives a PGR and not enough crops are treated in many seasons,” he added.He said that on-going work by BASF has shown importance of assessing the size of the crop canopy at the start of stem extension, ie at 30 per cent crop cover (Green Area Index 0.3), as once the crop canopy increases above a GAI 1 then the lodging risk increases rapidly.Varietal lodging scores, the GAI at, or just before, the start of stem extension and the yield potential of a crop are the three main factors that will determine lodging risk, he suggested.Turning to disease control in barley and the physiological response to fungicides, Dr Berry commented that trials work had demonstrated that where disease pressure is high, fungicide treatments applied at T1 (GS25-GS30) and at T2 (GS37-49) will be required to maintain yields.
In the absence of visible disease, a single application of prothioconazole + pyraclostrobin at T2 was likely to give barley a physiological yield benefit of 0.3-0.6t/ha, through greater seeds/m2 and seed size, he concluded.   Septoria conclusions
– Differences between azoles Proline and Ignite were seen only in protectant activity.- Solo SDHIs Vertisan and Imtrex were highly active on septoria.- SDHI/azole mixtures Adexar (fluxapyroxad + epoxiconazole), Aviator Xpro (bixafen + prothioconazole) and Vertisan + Ignite, were closely matched for septoria control and superior to solo SDHIs.- Multisite products Bravo (chlorothalonil) and Phoenix (folpet) remain valuable as protectants.Rust conclusions
– Straight SDHIs Vertisan and Imtrex showed activity on both rusts, but were more effective on brown rust.- Phoenix had no effect on brown rust but low level of activity on yellow rust (neither disease is currently on the label)?- Comet remains highly effective against brown rust, and Ignite most effective against yellow rust.- SDHI/azole mixtures more robust than solo SDHIs across yield and overall disease.


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