The Agriculture and Horticulture Development Board (AHDB) has released fungicide performance data for a recently authorised cereal fungicide – Plaxium.

The product has shown useful broad-spectrum efficacy in wheat and barley trials and provides a useful option to help manage several major cereal diseases.

Plaxium (from Bayer CropScience Limited) was approved for use in Great Britain by the Health and Safety Executive (HSE) in November 2024. It is a three-way formulation, comprising two succinate dehydrogenase inhibitors (SDHIs) – fluopyram and isoflucypram (also known as iblon) – and the demethylation inhibitor (DMI) prothioconazole. 

The AHDB fungicide performance project has tested the product under code in winter wheat and winter barley trials over several years.

ADAS' Jonathan Blake, who works on the trials, said: "We test products under code and can release independent performance data soon after approval for use has been granted."

To highlight differences between treatments for each target disease, the fungicide performance cereal trials are conducted in high-risk locations, using highly susceptible varieties and a single spray timing.

This approach creates a tough test for fungicides, so disease and yield differences observed in the trials may not reflect those seen in commercial settings.

The main advantage of the trials is that they reveal the relative performance of fungicide products.

AHDB released the annual update to the fungicide dose-response curves for wheat, barley and oilseed rape in December. The AHDB website has now been updated with results that reveal the relative performance of Plaxium.

Plaxium was tested in harvest 2019, 2020 and 2021 trials. The comments (below) are based on average performance over this three-year period.

Recent tests have focused on single active products and two-way mixtures, due to limited resources within the fungicide performance trials.

Wheat fungicide performance

In the wheat trials, Plaxium was evaluated for its efficacy against septoria tritici, brown rust and yellow rust.

Plaxium was highly effective against septoria tritici, in both protectant and eradicant situations, performing comparably to existing standards (such as Revystar XE and Univoq) and ahead of Ascra Xpro. In terms of yield, Plaxium gave a comparable yield response to both Univoq and Revystar XE and about a 0.3 t/ha increase compared to Ascra Xpro at the full label rate.

On yellow rust, Plaxium's activity was above Ascra Xpro and Revystar, comparable to Univoq and close to Elatus Era. These differences carried through to harvest, with Plaxium-treated plots yielding comparably to Univoq.

On brown rust, Plaxium offered superior control in trials compared to the other mixture products tested and was comparable in efficacy to Imtrex and Elatus Plus (two SDHIs that were highly effective solo actives on brown rust at the time of testing). Plaxium achieved a yield response comparable to Revystar and higher than the other products tested. Since 2021, changes in the brown rust population appear to have reduced the field activity of at least one SDHI: benzovindiflupyr (in Elatus Plus). It is currently unclear if other SDHIs have been affected.    

The results highlight the consistency in the performance of Plaxium and its broad-spectrum activity against major foliar pathogens of wheat.

NIAB's Stuart Knight, who also works on the trials, said: "The wheat trials indicate a clear efficacy and yield-response advantage for Plaxium compared to Ascra Xpro. This reflects the boost to foliar disease activity provided by isoflucypram, in place of bixafen, in this three-way mixture."    

Barley fungicide performance

In the barley trials, Plaxium was evaluated for its efficacy against rhynchosporium, net blotch, ramularia and powdery mildew. It showed good efficacy against all four diseases.

SRUC's Fiona Burnett, one the trial partners and chair of the UK Fungicide Resistance Action Group (FRAG), said: "Plaxium adds another robust mixture option for the control of barley diseases and is carefully stewarded to manage resistance risk."

Against rhynchosporium, in both protectant and eradicant situations, Plaxium gave excellent disease control, comparable to or better than Siltra Xpro and Ascra Xpro, and similar to the control provided by the solo active product Miravis Plus.

Similarly, against net blotch, Plaxium showed a very high level of efficacy, even at 50% of the label rate, performing comparably to Miravis Plus and Ascra Xpro.

Control of ramularia with Plaxium matched that obtained with Revystar XE and was slightly better than Ascra Xpro.

Plaxium gave the highest level of protectant activity against powdery mildew of the broad-spectrum products tested, although disease pressure was relatively low in these trials.

Resistance management

Use of Plaxium is limited to one application per crop. As a fungicide comprising two modes of action (a co-formulation of two SDHIs and one DMI), Plaxium supports resistance management strategies. Its use will lower the risk of resistant strains dominating compared to single-active fungicides.

By incorporating multi-mode-of-action fungicides into a well-structured resistance management strategy, growers can effectively manage major cereal diseases and reduce the long-term risk of resistance development. This is in accordance with the FRAG-UK guidelines (ahdb.org.uk/frag).

Plaxium is authorised for use in winter and spring wheat, barley, rye, triticale, spelt and oats. It can be used up to growth stage 61 for all cereal crops. A maximum of 75 g/ha isoflucypram may be applied every two years.

For the latest fungicide performance data, visit ahdb.org.uk/fungicide-performance