Mitigate resistance risk with use of different triazoles in early fungicide sprays advises agronomist Mike Thornton of ProCam

    Following a combination of recent milder winters followed by cooler, wet spring weather conditions across much of the UK, both brown and yellow rust are cycling more quickly during the winter period leading to higher levels of rust inoculum in crops at T1 says Mike Thornton, Head of Crop Production, at ProCam UK.

    According to Mike, warmer winter weather and later drilling windows for many growers in order to ease grassweed pressures have exacerbated yellow rust issues and made early season cereal disease control a much greater challenge.

    He says” It’s a difficult conundrum for growers. Later drilling offers them better prospects for septoria control but, conversely creates a greater risk of yellow rust because crops are usually under more stress at that point given their root systems are not as fully developed. Cooler, wetter spring weather often means many growers can struggle to get a T0 fungicide spray onto crops in March. However, for those who are able to spray, I would always recommend the additional investment and security of a T0 spray to get on top of rust and other key diseases earlier to reduce resistance risk and protect yields.

      “With the loss of both epoxiconazole and flutriafol in the last 5 years, chemical options for growers at T0 are certainly more limited than they’ve been in the past. However, there are still a number of good actives out there for early season rust control, with the recommendation that a dual triazole approach is preferable to a single triazole to avoid situations when use of a single triazole can inadvertently select for certain populations of septoria, potentially making disease control much more difficult.

    “Combining 2 different triazoles, for example bromuconazole + tebuconazole in azole-based products such as Soleil, offers a solid option at T0 for combatting rust but also means you don’t select as vigorously for the same septoria strains. This then helps to avoid serious disease scenarios later in the spring – particularly when dealing with a forward crop with septoria present, a variety with low resistance to septoria, or if the grower is in a higher risk septoria area.

    “Different rust populations come with different sensitivities, so developing good resistance management strategies within any fungicide programme comes down to mixing different actives to gain the broadest spectrum of control and reduce risk. Using different azoles at T0, such as bromuconazole and tebuconazole, also takes the pressure off more popular azoles such as prothioconazole that are often being used as either a straight or within mixes at both T1 and T2” concludes Mike.

         Simon Leak, Business Manager Crop Solutions for Sumitomo Chemical (UK), supports Mike’s call for growers to reconsider the use of a T0 spray to hold off the development of rust until the T1 timing.

      He adds” T0 is generally a cost-effective holding spray to control early developing rust and hold back septoria before the first main spray timing at T1. Of the options out there, triazoles are still the most popular in that they are cost-effective and also offer some activity on septoria and eyespot. Soleil (bromuconazole + tebuconazole) is a solid option at T0 for its control of rust and eyespot but can also be applied up to growth stage 65 as it delivers very good Fusarium control at T3. It’s a flexible tank mix option, can be applied in all soil conditions and performs equally well on both winter and spring wheat, rye and triticale.

     “Mike’s point regarding the benefit of changing the triazole mix to improve resistance management is certainly valid given that different azoles are active on different strains of septoria and are preferable to using the same azole actives throughout a fungicide programme – albeit in mixtures with other chemistry.

  “Controlling both brown and yellow rust effectively is a significant challenge and, with the increasing threat from these diseases and the possibility that tebuconazole may disappear from the armoury in the near future, the answer to future control of rust may come from a new active ingredient from Sumitomo Chemical known as Indiflin (inpyrfluxam), currently in the CRD regulatory system. An SDHI, it’s already on the market globally, targeting diseases such as soybean rust.

   “Indiflin will, in general, be used at T1 or T2 for the control of yellow and brown rust. In UK trials, it has excelled, even when up against the severe brown rust infections that many growers experienced during the 2024 harvest season” he concludes.