Epoxiconazole: How to fill the fungicide gap
© Tim Scrivener Epoxiconazole has been a familiar component in the disease control programmes of cereal and sugar beet crops for almost 20 years.
First registered in 1993 by BASF, an EU ban in April 2020 and the subsequent decision by the Chemicals Regulation Division that products containing epoxiconazole can’t be used or stored after 31 October 2021 in the UK, means that it is now in its last season.
Without it, growers are reliant on the remaining azoles – not all of which have the same strengths or price tag as epoxiconazole does – with alternative solutions based on other chemistry also being sought.
See also: Tackling rust and chocolate spot in beans post chlorothalonil
Preventing the over-application of the most obvious replacement, prothioconazole, is a key aim, as growers and agronomists work together to protect remaining chemistry.
While existing products containing epoxiconazole can still be used for another six months, the reality is that supplies are almost non-existent.
Unless stocks went on to farm last autumn, there’s little chance of getting hold of any this year.
Yellow rust control
The loss of epoxiconazole leaves a definite hole, says Chris Bean, technical director of Zantra, who believes that it wouldn’t be such a blow if the yellow rust situation was less dynamic.
“New strains of yellow rust are making the disease much more of a feature,” he says.
“We can’t rely on variety resistance ratings anymore, which means we don’t know where yellow rust is going to strike next. So that’s a concern without epoxiconazole.”
Epoxiconazole was very good on yellow rust and it didn’t do a bad job on septoria, so it had an established place in cost-effective cereal disease control programmes, he adds.
While prothioconazole can plug the septoria gap, it is less effective on yellow and brown rust than epoxiconazole was.
The SDHIs also have some activity on yellow rust, as do some of the new materials such as Revystar.
“What we have still got will need some assistance,” says Mr Bean.
“Remember that fenpropimorph has also gone and that was useful where rust was concerned.”
Alternative actives
One obvious replacement is tebuconazole, he highlights. “It’s pretty good on yellow rust, but less so on septoria.
“There’s also metconazole, but it hasn’t got the edge on septoria either and comes in at a similar cost to prothioconazole – making it more expensive than tebuconazole.”
Another route is to consider a prothioconazole/tebuconazole co-form, of which there are a few.
“They’re effective and were widely used when we had varieties such as Oakley, which were very susceptible to yellow rust,” he advises.
“They really proved themselves then and the trials data showed that you could often get a better overall response to prothioconazole/tebuconazole mixes than with epoxiconazole.”
However, they will be slightly more expensive, adding £5/ha-plus when compared to an equivalent dose of epoxiconazole, but with a higher risk of rust and few other options, then these products could have a place at T1 and T2, depending on the season and disease pressure.
Early sprays
For a T0 treatment to get on top of rust, tebuconazole will go a good job, he continues, but will be lightweight on any septoria present.
“There are also options such as tebuconazole/prochloraz products at this timing.
“Where rust is already being seen and there’s a history of the disease in the area, a T0 is necessary.”
Strobilurins are still effective on yellow rust and are another option at T0, but must only be used twice in a programme, so an azoxystrobin/tebuconazole mix could also feature.
“It will alleviate take-all pressure too, so has a place on second wheats.
“Where Group 1 wheats feature in the rotation, adding azoxystrobin at T1 and T2 could help with both rust control and nitrogen scavenging, to meet protein targets.”
Fenpropimorph, which has also gone, had become less effective on mildew, but was a useful way of dealing with a rust outbreak and allowed short-term eradication when mixed with other actives.
“We’ve lost two active ingredients that wouldn’t have mattered if we weren’t struggling with an ever-changing yellow rust population and if newer chemistry was stronger against it,” concludes Mr Bean.
“Growers and agronomists must remain vigilant.”
Keeping costs in check
Losing active ingredients is becoming the norm and the industry needs to learn to cope without them, believes independent agronomist James Rimmer of CCC Agronomy.
“We knew this was coming so we need to formulate a plan and get on,” he says.
“One of the issues of securing supplies last autumn is that we had no idea what the price of partner products would be. As a result, many didn’t go down that route.”
Although it’s not ideal, there are ways of filling the hole left by epoxiconazole’s departure, but most of them are more expensive, he adds.
“The obvious replacement is prothioconazole. At T1, it adds mildew and eyespot control to the mix, which are useful extras.”
In wheat, both epoxiconazole and prothioconazole control the same strains of septoria, but they do differ when it comes to yellow rust and that’s where its loss will be noticed most, he notes.
“Epoxiconazole was so good at controlling early yellow rust. Providing you put enough on at T1, it did a really decent job.”
As yellow rust is an annual challenge for Mr Rimmer in Kent, he will be looking at the use of tebuconazole at T0 and also at the strobilurins, which are still active on the disease.
In the field, he is seeing plenty of yellow rust in crops already and will be keeping a close eye on its development, after the cold spell in February failed to put a dent in it.
“We know that there are new races around and that variety resistance ratings aren’t reliable, so we are on standby.
“Yellow rust remains easy to control with the right chemistry, even if the options are narrowing.”
Losing chlorothalonil was the bigger blow, he reckons.
Fungicide programmes are going to get more expensive without it, so the emphasis should be on spray timings.
“It might be possible to get away with just one folpet application and save about £9/ha, but if septoria pressure is high then you will need two. The anti-resistance reasons are still valid.”
