Cereals 2010: Fungicide isopyrazam to be targeted at T1, T2

Carboxamide fungicide, isopyrazam, will be targeted at both T1 and T2 markets in wheat, should it be approved in time for next spring, Syngenta‘s Paul Varney said.

“We cannot guarantee registration for 2011, but we are hopeful.”

Its spectrum of activity with strengths against septoria, rusts with some activity on eyespot and mildew made it suitable for both main timings in wheat, his colleague David Ranner said. “We don’t see it as a T3 product, as it doesn’t have good activity against fusarium.”

Similarly to Bayer’s carboxamide fungicide, bixafen, isopyrazam gives longer lasting disease control than current standards. “Last year we sprayed at GS33 and let it run until disease control broke down. With triazoles plus chlorothalonil that was six weeks, with isopyrazam it was eight weeks.”

That could impact on what growers sprayed at T3, providing rates at flag leaf were kept up. “It will allow you to time your T3 better; there will be no need to rush back in for disease control.”

In-depth biochemical and modelling studies have helped Syngenta optimise isopyrazam’s structure to make sure it fits tightly in the target site of the fungicide and ensure maximum potency.

Knowing the mode of action enabled researchers to develop a test for potency early in development, the firm’s Andy Corran explained. “We could then vary chemical groups around the molecule and test for best potency, and led us to optimise the chemistry.”

Clever modelling of both the fungus and isopyrazam also helped the firm optimise the fungicide, he said.

By X-raying a pure solution of the enzyme protein in the fungus that the active ingredient binds to, the scientists were able to build a 3-D model of the active site, he explained. “Then we could look at how the active ingredient binds into the active site. The more tightly it binds, the more activity and the lower the use rate.”

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