Wheat fungicide performance data released for a new SDHI option

As the fungicide performance trial series enters its thirtieth year, we examine the latest efficacy data, including results for a new SDHI option in wheat.

This article includes conclusions from the latest fungicide performance results for the control of septoria tritici in winter wheat. It is based on a fungicide performance presentation delivered by ADAS’ Rebecca Joynt at the online AHDB Agronomy Conference (7 December 2023).

Running since 1994, our fungicide performance work provides high-quality, independent information on the efficacy of fungicides against key diseases in wheat, barley and oilseed rape.

Fungicides faced a tough septoria tritici test in 2023. A relatively wet March and cool April boosted septoria disease levels in many areas – as observed in fungicide performance trials, Recommended Lists (RL) trials and commercial crops.

In RL trials, despite the use of a robust fungicide programme, the disease was commonly seen on the most susceptible varieties. In some trials, it looked like the disease could run out of control. However, the hot, dry spell in June helped to curb disease development.

As RL disease ratings are normally based on a three-year data set, ratings did not reduce across the board in the latest RL (2024/25), released on 27 November 2023. This is good news, as varietal resistance is the foundation of disease control, helping to underpin less intensive fungicide programmes.

To maximise treatment differences in the fungicide performance trials, the project uses:

• Relatively high-risk sites for the target disease
• Highly susceptible varieties to the target disease
• One spray timing

Septoria tritici is the most damaging foliar disease on UK winter wheat. Its economic importance is reflected in the number of fungicide performance trials. In 2023, septoria tritici efficacy data was generated at seven trial sites (across England, Wales, Ireland and Scotland) – as shown in the table below.

Fungicide performance site information

*Trials were considered as having either protectant (P), eradicant (E) or mixed (M) activity. **Septoria tritici disease rating (in brackets) as published in RL 2023/24, except KWS Barrel (RL 2022/23). Note: Sometimes cover sprays (not active against the target disease) are used to control other diseases.

The team follows project ground rules to help produce the most valuable data possible. For example, they compare new (pre-registration) active ingredients against established standards. This allows the rapid release of efficacy data when new products hit the market.

For the first time, the 2023 presentation included information on a new SDHI-based product called Vimoy (from Bayer), which has isoflucypram as the active ingredient.

The table, below, shows the products used in the 2023 septoria trials.

Treatment details

*Arizona and Proline 275 only tested at full dose against septoria.

A further six unregistered products were tested in 2023, which will allow the data to be released upon registration.

The trials test most fungicides at four doses, which allows the classic ‘dose-response’ curves to be created. These show how much more disease control or yield uplift is associated with higher doses.

For the cereal trials, the doses are quarter, half, full and double the recommended label rate (the latter improves the ‘fit’ of curves, but these results are not published online).

Like the RL trials, over-year data helps deal with seasonal effects and provides a good indication of average performance (across leaf layers).

For example, the figure (below) shows the average performance against septoria in a protectant situation over three years (2021–23) and 17 trials.

The main conclusions for fungicide performance for septoria were:

• Of the approved actives tested (straights), fenpicoxamid (Peqtiga) gave the highest level of septoria control
• Isoflucypram (Vimoy) and mefentrifluconazole (Myresa) also provided good activity (especially as protectants)
• Mixtures (Univoq, Revystar XE) gave more robust control than the straights
• No major shifts in fungicide sensitivity detected in septoria pathogen populations in 2023

The final point is particularly welcome news. However, it remains important to check labels and follow resistance management guidance to continue to protect efficacy. This includes combining septoria-active-fungicide mode of action groups across the programme and protecting straights in mixtures.

The main conclusion for wheat rusts were:

• Good yellow rust control from isoflucypram and mefentrifluconazole, but benzovindiflupyr (Elatus Plus) and mixtures (Univoq, Revystar XE) were the most effective
• Isoflucypram and mefentrifluconazole were both highly active against brown rust

The active ingredient Isoflucypram is marketed as ‘Iblon’ by Bayer. It demonstrated broad-spectrum activity against the diseases evaluated in these trials. Using it in conjunction with prothioconazole is a good resistance management tactic and may improve overall control, although no data on this was presented at the Agronomy Conference.

The full presentation includes fungicide performance data for the following crops and diseases:

• Wheat: septoria tritici, yellow rust, brown rust and fusarium
• Barley: rhynchosporium, net blotch, ramularia
• Oilseed rape: phoma stem canker and light leaf spot