Fungicide performance on winter wheat

Between 2011 and 2014, the efficacy of new and existing fungicides was tested in 28 replicated trials in wheat across the UK and Ireland. Products were tested on the major foliar diseases of wheat, and each year there were 4 trials looking at Septoria tritici, and one trial of each targeting yellow rust, brown rust and mildew. The fungicides tested included new active ingredients from the succinate de-hydrogenase inhibitor (SDHI) group, the multi-site folpet, specific mildewicides and new mixtures of existing chemistry, tested alongside core treatments representing current standards. Some new fungicides tested have since been approved and are registered for use, whilst others are yet to be registered. The fungicides were tested by applying single applications at a range of rates ranging from quarter to double the full recommended label rate. Double dose treatments were included in the trials to accurately fit dose response curves (by better estimating the lower asymptote of the curve). Such doses are not legal for use in commercial crops. One of the Septoria tritici trials each year included a new trial design to investigate how the width of the effective spray window differs between fungicides. This was tested by applying half label rate treatments at one of 5 timings during the emergence of the final three leaves, with the efficacy on each leaf being assessed.

Straight products were tested in the trial series to investigate their efficacy, but in practice, fungicides at moderate or high risk of resistance, such as the azoles and the SDHIs, should always be applied in mixture with a partner of a different mode of action at a dose that will provide good efficacy on the target disease.

On Septoria tritici, Bravo (chlorothalonil) continued to provide effective protectant activity. Phoenix (folpet) also gave a useful level of protectant activity, although, when compared at equivalent proportions of label doses it was less effective than chlorothalonil. Products based on epoxiconazole and prothioconazole both gave a similar level of protectant and eradicant activity against Septoria tritici, although efficacy was lower than in previous seasons in both protectant and eradicant situations. The straight SDHI products Imtrex (fluxapyroxad) and Vertisan (penthiopyrad) had more effective protectant and eradicant activity against Septoria tritici than the azoles. Isopyrazam gave a similar level of protectant activity to Imtrex and Vertisan, but appeared to have less eradicant activity. The SDHI mixtures Aviator Xpro (prothioconazole + bixafen), Adexar (epoxiconazole + fluxapyroxad) and Vertisan + Ignite (penthiopyrad + epoxiconazole) all gave a higher level of protectant and eradicant activity than either the SDHI or azole components alone. Seguris (epoxiconazole + isopyrazam) gave a similar level of protectant activity to the other SDHIazole mixtures, but appeared to have less eradicant activity. Results from the new trial design indicated that products may differ in their effective width of spray window. Significant differences between products were identified by the analysis. The spray window for the straight SDHI Imtrex was estimated to be wider than isopyrazam, and the spray window for the SDHI-azole mixtures Aviator Xpro and Adexar estimated to be wider than Seguris. However, isopyrazam and Seguris were at least as effective as the other straight SDHI or mixture products, respectively, when applied at the optimum timing.

Powdery mildew was targeted at Fife for 4 seasons, and relied on natural infection to occur. Despite selection of the highly susceptible variety Claire, levels of powdery mildew were too low to permit assessment. These sites contributed data on Septoria tritici instead.

All products containing epoxiconazole (Ignite, Brutus, Seguris and Adexar) gave highly effective control of yellow rust, even at low doses. Proline (prothioconazole) and Comet (pyraclostrobin) also had good activity on yellow rust but were not as effective as epoxiconazole-based treatments. The straight SDHI products Imtrex and Vertisan had a useful level of activity against yellow rust, which could add to the control of yellow rust when used in mixtures. The SDHI-azole mixtures Adexar, Seguris and Vertisan + Ignite all gave effective control of yellow rust. In two of the four seasons reported here, Aviator Xpro gave less effective control of yellow rust compared to the other SDHIazole mixtures tested.

Although only tested in one of the two brown rust trials reported here, the strobilurin Comet gave highly effective control of brown rust, even at low doses. The straight SDHIs Imtrex, Vertisan and isopyrazam gave effective control of brown rust. Ignite showed good activity against brown rust, and although not as effective as Comet, gave more effective control of brown rust than Proline. The SDHI-azole combinations Adexar, Aviator Xpro, Vertisan + Ignite and Seguris all gave very effective control of brown rust.