Growers are being warned not to ditch multi-site fungicides as the chlorothalonil deadline looms, according to the latest advice from Adama. Charlotte Cunningham reports.

With the final use-up date for chlorothalonil rapidly approaching, arable growers in the UK could benefit from switching to folpet to maintain effective protection against cereal diseases – such as septoria in wheat and rhynchosporium and ramularia in barley – according to Andy Bailey, fungicides technical specialist for ADAMA.

“In recent years, the efficacy of some of the principal wheat and barley ‘single-site’ SDHI, azole and strobilurin fungicides has been eroded by the development of resistant disease strains,” he explains. “Meanwhile, other active ingredients, including chlorothalonil, have been lost to regulatory restrictions, thereby making the effective control of key wheat and barley diseases increasingly difficult to achieve.

“Growers must therefore think carefully about how they structure their fungicide treatments in the second half of the spring to ensure their crops remain properly protected.”

Blow to growers

Chlorothalonil has been the ‘go-to’ multi-site fungicide for many years but can’t be used beyond the 20th May after the EU voted to revoke its license – a huge blow to growers, adds Andy. “As a multi-site fungicide which targets multiple metabolic sites within a pathogen, chlorothalonil has performed two important functions: providing effective disease control and reducing the risk of further resistance.

“With the loss of this popular fungicide there is a danger that, beyond the 20 May cut-off date, growers may choose simply not to replace the multi-site component of their crop protection programmes.”

However, this would be a dangerous backward step, warns Andy. “It would put crops at increased risk of infection and heighten the resistance risk for other modes of action.”

To compensate for the loss of chlorothalonil, Andy is urging growers to switch to folpet as an alternative. “With folpet and mancozeb the only multi-sites currently registered, Arizona (500 g/L folpet) is the most effective option when it comes to replacing chlorothalonil.

“It’s flexible enough to be used at T0, T1 and T2 (at a maximum individual application rate of 1.5 L/ha and a total application rate of 3 L/ha) to protect wheat against septoria and barley against rhynchosporium and ramularia.

Activity against yellow rust

As well as this Arizona also provides some activity against yellow rust in wheat, he adds. “This is either as a standalone active or as a mix partner for straight SDHI fungicides and offers the additional advantage of not interfering with the curative kickback activity of azoles.

“This is an important factor where active rust is present as it’s crucial to maximise the speed of activity and the curative effect of the azole in order to combat infections effectively.”

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