A new cereal fungicide boasting greater protection of crops against septoria, as well as providing yield improvement, seems to have arrived just in time for growers and agronomists. Dominic Kilburn reports.
In light of the well-documented decline in triazole efficacy against key cereal disease septoria, the imminent loss of multi-site fungicide chlorothalonil and the evolving picture of SDHI resistance, BASF’s launch of a new cereal fungicide couldn’t have come at a better time for UK growers, believes the company.
Revystar XE has received authorisation on all cereal crops and, according to BASF, offers an “impressive leap” in the control of septoria in wheat over current products, while also delivering improved yields.
Other diseases controlled on its broad-spectrum label include yellow and brown rust, as well as net blotch, rhynchosporium and ramularia in barley.
In addition, BASF believes its product will play a key role in protecting SDHI chemistry for the future.
Revystar XE is based on new active ingredient Revysol (mefentrifluconazole) and Xemium (fluxapyroxad) – the latter already found in BASF’s SDHI portfolio of Adexar and Librax. However, according to the company’s senior principal scientist, fungicide development, Dr Rosie Bryson, Revysol – the first isopropanol azole on the market – is unique in the way it binds to the fungus, providing reliable control of all known strains of septoria. “Revysol has a flexible conformation which allows the molecule to move in lots of directions and adapt to the binding pocket of the fungal enzyme.
“When we have resistant mutations, conventional triazoles can’t ‘fit’ into the fungus, whereas Revysol can with its flexibility,” she explained.
BASF head of business development, Steve Dennis added that Revysol’s binding power, which destroys the target fungus, is, on average, 100 times more powerful than conventional azoles, resulting in stronger efficacy. “There’s a lot of variation between fungicide binding power and Revysol binds five times as much as the nearest fungicide performance, and is a key reason why it is as effective as it is.
“Septoria is an increasing challenge due to eroding triazole efficacy, a loss of actives and a more extreme climate. One thing is clear: we need higher efficacy and the control of varied septoria populations and shifted strains.”
In AHDB septoria protectant trials (2017–2019), Revystar XE at half- and full-label rate demonstrated improved control over other SDHI products Ascra Xpro (bixfen + fluopyram + prothioconazole) and Elatus Era (benzovindiflupyr + prothioconazole), while a jump in yield (2019) was also seen with the same product comparisons.
Trials also demonstrated very good brown rust control and yellow rust control similar to other SDHIs. “We wouldn’t claim yellow rust control with Revystar is as good as its control of septoria or brown rust, but it is as good as other products,” said Mr Dennis.
“Revystar combines the best septoria control with broad-spectrum efficacy against other key diseases in wheat,” he added.
According to Mr Dennis, that broad-spectrum activity is extended to the main barley diseases and importantly, he said, including ramularia. “Ramularia is a disease we need to understand more, but with prothioconazole losing its performance, Revystar, after chlorothalonil, is the best active for ramularia by a long way.”
In addition to a high level of protectant activity against septoria, Mr Dennis pointed out that Reysol shows excellent curative activity against the disease. “To have curative activity the fungicide has to follow the disease inside the leaf and the quicker it can do this the better. Revysol has very rapid leaf uptake – in one hour it equals prothioconazole’s uptake in one day – and the active is taken up quickly and sits just below the leaf surface where it is naturally protected against external conditions like rain, providing excellent rainfastness, or UV sunlight.
“Revysol inner leaf reservoirs are formed resulting in slow and consistent distribution of the product along the leaf length, also leading to long-lasting efficacy,” explained Mr Dennis.
He said that a study of farmer perceptions across the UK and Europe in the run up to the T2 timing in 2019, showed that most thought their crops looked clean as the flag leaf was coming out. “However, after leaf collection and analysis a lot of septoria was in evidence from the latent phase and many crops needed a curative treatment despite well timed sprays.
“It showed that growers at T2 probably don’t realise the level of septoria they have in the crop at the time and that curative conditions are common even if the crop looks healthy,” he added.
In testing (straight) Revysol efficacy in field conditions against natural septoria infestations, as well as high densities of (flag leaf timed) inoculated DMI (triazole)-adapted septoria strains, ADAS principal crop pathology researcher Dr Julie Smith said that the product continued to provide efficacy long after the application (made five days after disease inoculation), compared with Proline. “Where 80 per cent of the flag leaf was covered in septoria, even at these pressures good control was achieved,” she commented.
She added that Revysol also outperformed Proline in ADAS Healthy Area Duration (HAD) trials – a combined measurement of healthy canopy size and duration – resulting in a yield benefit.
When considering the relevance of Revysol when used in combination with wheat varieties with good septoria resistance, Dr Smith confirmed that, irrespective of varietal resistance, disease pressure or septoria populations present, there is a response and benefit in using Revysol. “Yield response in these trials was up in all situations following just one application at the T2 timing, and with nothing applied prior to that.
“It’s an amazing yield response from an azole,” she added.
As part of BASF’s Real Results initiative, Kent grower Richard Budd trialed Revystar at T1 and T2 timings in a 14ha crop of KWS Lili at Stevens Farm, Hawkhurst, in 2019. He compared it with his ‘farm standard’ cereal fungicide programme.
In what was a low disease year, Mr Budd said that, through much of the growing season, there was no obvious difference across the trial compared with the farm standard treatment. However, in late June to mid-July, he reckoned the Revystar trial remained greener for longer – by as much as 10 days.
When it came to yield, the farm standard-treated crop delivered 13.89t/ha while the Revystar-treated plot resulted in an additional 0.99t/ha. “Because it was greener for longer, that translated into an additional 1t/ha over the farm standard,” commented Mr Budd.
“If we haven’t got a green crop then we can’t accumulate yield,” he added.
For 2020, he is going to start with Revystar at T1 – its curative properties able to clean up any septoria that has come through the winter – with a repeat dose at T2 depending on the season. Or, he might drop the T0 and go with an early T1 of Revystar, he suggested.
“If we have a clean crop after T1 then there is the option to go with a cheaper product at T2, or to use Revystar again,” he said.
Use of multi-sites
BASF says that it is fully committed to the responsible stewardship of its new active ingredient Revysol and, as such, it will be sold in formulation with Xemium. The combination of these two different modes of action ensures unique resistance management and maximises the protection of SDHIs, the company states.
BASF recommends Revystar with chlorothalonil while it remains available, and the company will evaluate the ability of other multi-site fungicides, such as folpet, as resistant management tools.