Winter Wheat T1 Fungicide Strategy

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Madeline Heath
5 years ago
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Spring 2019 Agronomy Date: 05/4/19 Ella Crawford ella.crawford@bayer.

biomass than expected. This means the disease risk on these varieties could be higher than you might expect from their RL scores.

1 Spring 2019 Agronomy Date: 05/4/19 Ella Crawford Winter Wheat T1 Fungicide Strategy Key points Despite later drilling in many situations, the warm winter has allowed even late October drilled crops to accumulate significantly more biomass than expected. This means the disease risk on these varieties could be higher than you might expect from their RL scores. Aim the T1 timing for when the majority of main tillers have final leaf 3 at least ¾ emerged. T1 sprays should contain robust doses of prothioconazole or epoxiconazole as a base. A multisite product should be added in almost every occasion. There is a lot of debate in the press at the moment about the decision to include an SDHI or not at T1. This should be based on drilling date, variety, your attitude to risk, whether a T0 was applied, spring weather conditions, your ability to apply T1 and T2 fungicides on time, phases of the moon, your mother s maiden name YOU SHOULD GO WITH WHAT YOU FEEL COMFORTABLE WITH! A non SDHI strategy can be effective at T1 but does require the timing to be spot on. If T1 is delayed by bad weather then only SDHI chemistry provides the kickback that may be required. Alongside their variable foliar disease scores, a large number of the current RL varieties have poor eyespot ratings (5 or below). Recommendations SDHI based options l/ha Aviator 235 Xpro + multisite or l/ha AscraXpro + multisite AscraXpro is a stronger Septoria option than Aviator 235 Xpro at T1 but lower PTZ loading (see triazole loading section of this update) means Aviator 235 Xpro would be better on stem based disease. The 1 l/ha dose of AscraXpro or Aviator 235 Xpro would be suitable in all but the very highest Septoria pressures (early drilled, very poor Septoria scored varieties with no T0 applied may require 1.2 l/ha AscraXpro or 1.25 l/ha Aviator 235 Xpro). If active rust is present in crops at T1 then the addition of 100g tebuconazole (0.4 l/ha of a 250 g/l formulation) for very little extra cost is worthwhile. Tebuconazole is also available in co-form with CTL and this could be the cheapest way to buy them to mix if required. CTL should only ever be removed from the T1 spray if rampant rust has taken off in the crop in this case spend the CTL money on a high dose of tebuconazole or a strobilurin to add to the mix. Strobilurin fungicides can be added into Aviator 235 Xpro or AscraXpro to give additional rust activity. Pyraclostrobin or azoxystrobin would be the obvious candidates or alternatively look at the cost of 1.35 l/ha Firefly mixed with a straight SDHI (eg. Imtrex or Ceratavo) + multisite.

2 Non SDHI based options (for late drilled crops of Septoria resistant varieties) l/ha Proline + multisite Delivers 75% prothioconazole dose to cover foliar disease and give stem based activity. Will need addition of tebuconazole or a rust active strobilurin if there is active rust in the crop at T1. Alternatively consider swapping to Firefly below l/ha Firefly + multisite 66 75% PTZ loading (at these dose rates) with strong rust strobilurin. Depending on prices, you could add a straight SDHI (eg. Imtrex or Ceratavo) into this mix as an alternative to Aviator / Ascra + Comet + multisite. Triazole Loading The Big Difference Between T1 Products Bixafen, fluxapyroxad and benzovindiflupyr are all excellent SDHI actives and any programme based on products containing these is likely to be robust enough in most disease scenarios assuming they are used at sensible doses. However one area where they do differ greatly is in the amount of triazole partner supporting and protecting the SDHI component. The table below shows the triazole dose in the common T1 options. The lower the triazole dose in the T1 mix, the harder the SDHI component has to work to maintain efficacy. Ideally we should be giving the SDHI the minimal workload as this is a far better anti-resistance strategy. Aim for as high a triazole dose as possible to give good efficacy and to assist with protection of the SDHI component of a mix. 4 years out of the last 5 prothioconazole has performed better than epoxiconazole in the AHDB appropriate fungicide dose trials. Unfortunately straight metconazole is not tested against Septoria in this work. Remember that to get effective activity against eyespot and Fusarium with prothioconazole then a minimum of 75% dose is required. Triazole Prothioconazole Epoxiconazole Metconazole Product Aviator Ascra Elatus Era Adexar Seguris Keystone Librax Product Dose Triazole Dose 1 80% % 1 65% % % % 1 50% % % 1 72% % 1 79% 1 50% %

cross resistance to each other i.e. if one stops working, then they all will.

3 Aviator vs Ascra and What s This Fluopyram All About? Most of the modern SDHI actives (bixafen in Aviator 235 Xpro and AscraXpro, fluxapyroxad in Adexar and Librax and benzovindiflupyr in Elatus Era) are pyrazole carboxamides and therefore have complete cross resistance to each other i.e. if one stops working, then they all will. Fluopyram (the other SDHI in AscraXpro) is a benzamide SDHI and so is slightly different to the other SDHIs in its Septoria selectivity profile. Fluopyram is less intrinsically active on Septoria than bixafen but its inclusion does contribute to the improved efficacy seen with AscraXpro. Despite it looking as if there is a very high overall amount of SDHI in AscraXpro (65g/l bixafen + 65g/l fluopyram) compared to other products, the mixed SDHI approach in AscraXpro is less of a resistance concern because o o Fluopyram has lower intrinsic activity on most Septoria isolates compared to bixafen. Simply increasing the dose applied of the stronger SDHIs (bixafen, fluxapyroxad or benzovindiflupyr) would just greatly increase the selection pressure on these pyrazole group actives. As mentioned in the Recommendations section AscraXpro is better on Septoria, Aviator 235 Xpro is better on stem based diseases. Fig 1 from Yamashita & Fraaije (Pest Management Science Vol 74) Comparing the EC50 for Septoria isolates of two pyrazole SDHIs - fluxapyroxad (in Adexar, Librax) and bixafen (in Aviator 235 Xpro) All the isolates are very close to the grey line indicating a high degree of correlation between the efficacies of the two actives. The results in the red circle indicate isolates that are more tolerant to both fluxapyroxad and bixafen. The blue circle results are isolates that are very sensitive to both these SDHIs. There are no results away from the line (purple and green zones) to indicate isolates that are sensitive to one of these SDHIs but more tolerant to the other. The p value is very low (<0.005) showing there is indeed a close correlation between results for fluxapyroxad and bixafen. Fig 2 also from Yamashita & Fraaije (Pest Management Science Vol 74) Comparing the EC50 for Septoria isolates of one pyrazole SDHI - fluxapyroxad (in Adexar, Librax) to that of the benzamide SDHI - fluopyram (in AscraXpro). In this comparison there is a much greater spread of results away from the grey line indicating less of a correlation between the actives than in the previous chart. There are still results in the red and blue circles meaning that, as in Fig 1, there are isolates tolerant (red) and sensitive (blue) to both SDHIs This time however, results can be found in the purple circle indicating more of a sensitivity to fluopyram than to fluxapyroxad, the result in the green circle shows the opposite. The p value here is much higher than in Fig 1 showing there not a close correlation between results for fluxapyroxad and fluopyram, even though a number of results do still fall on the grey line.

T1 Trials Data from 2019 2018 was not a good year for pulling out T1 differences especially on varieties with higher Septoria ratings but the trial series below did get some responses on Santiago and

4 T1 Trials Data from was not a good year for pulling out T1 differences especially on varieties with higher Septoria ratings but the trial series below did get some responses on Santiago and Trinity. Additional Information As previously mentioned in Perspective 6 (WW fungicide programme) there is lots of useful information on resistance management, appropriate doses, one vs two SDHIs etc. in the AHDB / FRAG Fungicide Futures booklet More information on the cross resistance (or otherwise) of the different SDHIs can be found in the paper by Yamashita & Fraaije (Pest Management Science Vol 74) using this link SDHI Cross Resistance Article. I m warning you for this one - brace yourselves and strap in tight!! ANNUAL SUBSCRIPTION FOR BAYER TECHNICAL UPDATES CP/67095/1819/g 2 CP points To register BASIS points please contact: michele@basis-reg.co.uk quoting the above BASIS reference.

5 Small Print Aviator 235 Xpro contains prothioconazole and bixafen. Ascra Xpro contains prothioconazole, fluopyram and bixafen. Proline contains prothioconazole. Firefly contains prothioconazole and fluoxastrobin. Aviator, Ascra, Proline & Firefly are registered Trade Marks of Bayer. All other brands listed may be Trade Marks of other manufacturers and proprietary rights may exist. Use plant protection products safely. Always read the label and product information before use. Pay attention to the risk indications and follow the safety precautions on the label. For further information visit or call Bayer on All information within Perspective is copyright of Bayer Crop Science Limited and may not be reproduced or distributed except with the express written consent of Bayer. The information contained herein has been compiled by Bayer to the best of its belief and for information purposes only. It should not be used as a substitute for specific recommendations and advice from a qualified agronomy professional. To the extent permissible by law Bayer bears no liability for damage or injury resulting from reliance on information given herein. If you no longer wish to receive the Perspective technical bulletins from me then please reply to this stating that you wish to unsubscribe. Crop Science Division, Bayer Crop Science Ltd., 230 Cambridge Science Park, Milton Road, Cambridge, CB4 0WB Bayer Crop Science Limited 2019

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