As featured in Arable Farming Magazine
Testing times for fungicides
by Arable Farming Magazine March issue
The annual review of AHDB’s fungicide performance trials helps inform disease control toolkit decisions for the coming season. Teresa Rush reports.
Last season provided a tough test for fungicides, with products challenged by late infection events in wheat crops in particular.
What then did the AHDB fungicide performance trials reveal? ADAS tested a range of products for their activity against septoria tritici at seven high risk sites: Rosemaund and Sutton Scotney in the south west of England, East Lothian, and Dundee in Scotland, Carlow in the south east of Ireland, Telford in the West Midlands and Cardigan in west Wales.
Applications were made at a range of spray timings at quarter, half and full rate doses to assess curative and protectant activity; multisite folpet was tested at a single rate.
Azoles Proline and Imtrex looked a fraction stronger than multisite Arizona in a protectant scenario at the full label rate, says ADAS principal research scientist and project leader Jonathan Blake, while solo azole Myresa performed well on septoria.
“Better than the performance we have seen from prothioconazole of late,” adds Mr Blake.
Mixtures Turning to mixtures, Revystar XE and Univoq were performing well and hard to separate, he says.
Curative data is available from four sites, but Mr Blake advises care is required with interpretation.
“Everything tends to perform less well in the curative situation and that is exactly what we see, with Imtrex and Proline not providing a huge amount of curative activity last year; Myresa certainly looking better and Univoq and Revystar are almost inseparable in terms of their activity.
Infection events “Be careful with interpreting curative data though; there are often numerous infection events which will have occurred on leaves prior to them being sprayed.
“On many occasions they have a level of septoria that is beyond control, so there may be 10-15% (level of infection) that no fungicide will control, so it is not an absolute value, it is more of a measure of how products will compare.”
But looking at protectant data over three seasons (2019-2021), everything looks better, he says.
“It was a tough test last year in the protectant scenario, with a lot of late infection events that will have challenged products applied some time prior to those infection events occurring, and 2020 was the opposite; a much easier protectant scenario, when everything performed very well.”
Fungicides applied as protectants, including Arizona, Imtrex and Proline, are giving around 50% control of septoria.
Among the mixtures, now including Ascra Xpro, which was not tested last year, but was tested in the previous two years, the performance of Revystar and Univoq are very similar, while, dose for dose, Ascra is a small step behind, says Mr Blake.
The curative data pattern over three seasons is very similar.
“Imtrex and Proline, over a three-year average, were not providing a huge amount of curative activity but the mixtures containing the new modes of action certainly are looking quite strong and Ascra is again a little bit off the pace in a curative scenario compared to the new products when compared dose for dose.
In terms of yield, Univoq and Revystar are looking similar; probably on the three-year average you would just give it to Univoq.”
How the performance of azoles, SDHIs and SDHI + azoles is changing over time is a key question and with the fungicide response trials running since 1994 – starting life as the Appropriate Dose Network – the data set gives a feel for where things are now, relative to where they have been.
Taking as an example the activity obtained from a full dose of prothioconazole over 20 years (2001-2021) applied in a protectant situation, Mr Blake highlights the 80-100% level of control obtained from a full label rate dose at the beginning of that period to the 20% control seen in 2021.
“It was working incredibly well, but gradually over a period of time its activity has declined.
We do see variation from one season to the next.
There are some years – 2010 – where it suddenly looked quite weak; 2021 was clearly quite a tough test and we saw poor control from prothioconazole when applied alone in a protect ant scenario in these trials.”
SDHI efficacy The much newer active, mefentrifluconazole from BASF is performing at levels similar to those seen with prothioconazole 10 or 15 years ago, he adds.
SDHIs are also showing a change in efficacy.
Back in 2016/17 the SDHI Imtrex was doing a fantastic job, says Mr Blake.
“It was giving us 75-80% control from a half or full label rate; last year that half or full label rate was giving us 30-40%, approximately half of what it was doing four or five years ago.
“There is clearly a change in efficacy there and quite a range of efficacy between sites; at one site it was performing very well, at another it was hardly giving us anything, so we are seeing it as a less robust and reliable tool, but it is still adding to efficacy and still helping.
“Fortunately, the mixtures are still holding up quite well.
It was a tough test last year but even with that it is difficult to pick out a decline.
“We’ve got [data for] Univoq and Revystar going back to 2017, although of course they have been registered much more recently than that.
One thing to note is when we initially looked at these products in 2017-2019, of the two products you would have picked Revystar ahead of Univoq.
I think the one thing we have seen in the last couple of years is they perform very much more similarly.”
Reflecting that yellow rust control in wheat is less about the product and more about the timing, Mr Blake says Peqtiga, containing the single active fenpicoxamid, was clearly adding some activity on yellow rust but was perhaps not quite as strong as Imtrex and Myresa.
“The two that have come out best at the lowest dose rates are Elatus Plus and Proline.
Revystar and Univoq came out almost identical in terms of their efficacy.
Mixtures tend to perform well on yellow rust and, if you did have a specific yellow rust problem, I can see Elatus Era might have a role to play.”
Results from three years of trials (2019-2021) show a similar pattern.
“Again, you would probably pick Elatus Era as being a little stronger than some of the others on the mixture side,” says Mr Blake.
“Yields can be an interesting test in such a trial.
A difference in duration of control by a week can make a significant difference in the yield we see.
It is quite hard to separate the products with a single active ingredient but you can see [among the mixtures] that Elatus Era is strong and will probably give you the best control of any of the SDHI/azoles that are out there.”
• On septoria, Univoq and Revystar are showing the highest level of activity
• The field activity of current SDHIs has declined since 2017
• On yellow rust, Elatus Era was particularly effective but all mixtures performed well
• Mefentrifluconazole and SDHIs tested were highly active on brown rust; fenpicoxamid and prothioconazole added useful activity
• Arizona (folpet) provided close to 30% control of septoria, reducing levels from 22% on average across the sites down to 15%
• All diseases were better controlled in protectant situations
• Prothioconazole and fluxapyroxad were both better at controlling rhynchosporium and net blotch
• Mefentrifluconazole adds efficacy on ramularia
• SDHIs bixafen and fluopyram add useful activity on net blotch, particularly in Ascra Xpro
Mixtures better in barley
Following its registration at the end of last season, Ascra Xpro is now available in barley, delivering 65g/litre bixafen + 65g/litre fluopyram + 130g/litre prothioconazole at the full label dose of 1.2 litres/hectare.
Mr Blake says: “One thing to note is it has a different full label rate in barley to that in wheat.
In wheat you can apply up to 1.5 litres per hectare, in barley it is 1.2 litres/ha and you can only apply that 1.2 litres/ha as a total dose.
“We’ve been using prothioconazole-based chemistry for a long time in barley and to give a comparison with Siltra, a combination of prothioconazole and bixafen, Ascra Xpro contains a bit more SDHI, a bit more bixafen in the full label rate and the addition of an extra SDHI in the form of fluopyram but it has got a little bit less prothioconazole.
“What does that bring? On rhynchosporium Proline is the go-to benchmark.
Ascra is performing very similarly to Proline on rhynchosporium.”
Imtrex also has very good activity on rhynchosporium and so it comes as no surprise that Revystar looks very strong as well, Mr Blake adds.
“One thing that comes out when you look at yields in the rhynchosporium trials is the mixtures tend to come out a little bit better, with Ascra and Revystar looking a little bit better than the solos of Imtrex and Proline.
Net blotch “In net blotch, we know Kayak in a protectant scenario will provide us with 30-50% control and can be a useful addition to fungicide programmes and the cyprodinil will add a little bit of mildew activity, so it can be quite useful early season.
“Ascra Xpro, Imtrex and Proline all performed well and similarly in a protectant scenario on net blotch.”
In a curative scenario there is some separation.
Comparing Ascra Xpro with Proline, the addition of the two SDHIs in Ascra improves control of net blotch.
Revystar and Imtrex are performing similarly to prothioconazole.
The toolbox for ramularia control is rather more limited, with Proline and Myresa available as single active products and Revystar XE as a mixture.
“Proline provides a level of control against ramularia, it is not very active; Myresa is clearly more active, although you have to apply quite a high dose of it to get a good level of control.
“Revystar follows an almost identical response to what we see from Myresa, primarily as it is the mefentrifluconazole in both that is driving that.
We don’t think Imtrex is adding much on ramularia protection,” says Mr Blake.