Published on 31/07/2025
Foundation for Arable Research monitoring, supported by all major crop protection suppliers, has been tracking the sensitivity of NZ Septoria strains to fungicides with different modes of action for multiple seasons.
“We now have a clear view of the changes happening in the NZ Septoria population,” says Matt Denton-Giles, Corteva field scientist.
Latest data for the 2025 harvest has yet to be finalised and reported, but 2024 results continued to show reductions in sensitivity to Group 3 (prothioconazole and epoxiconazole) and group 7 (fluxapyroxad and benzovindiflupyr) fungicides.
Several SDHI fungicides are exhibiting cross-resistance, where Septoria resistance to one fungicide active transfers to another.
Denton-Giles says the value of such monitoring lies in giving NZ growers early warning of what might lie ahead. Failure of any chemical group to fully control target pathogens because of resistance happens quickly.
“All you have to do is compare today’s cereal fungicide programmes in the United Kingdom and Europe to the programmes those growers were using five years ago.”
Grower awareness of the risks posed by resistance as a whole in the NZ arable sector is increasing, which is great, Denton-Giles says. But it’s very important that they take the next step, if they haven’t already, and adopt programmes that will help protect existing fungicide chemistry, even if it doesn’t seem like they need to right now.
“Some are probably still looking at this in terms of cost only, and others may not realise the full extent of the risk because they’re using a fair bit of chemistry that still works.
“No-one gets too worried when their sprays are still effective, but in fact that’s actually the critical time to review your current programme and make the changes necessary to ensure it remains sustainable in future years.”
UK growers for example no longer have access to some SDHI technology because of resistance. By contrast, the NZ industry has time to protect what it has, but only if change is implemented.
Corteva marketing manager Glen Surgenor says Questar, with its unique active ingredient Inatreq, remains a valuable disease management tool that must be used with care.
The first member of a new class of cereal fungicides, the picolinamides (Group 21), it has a different target site to all other fungicides currently applied for Septoria control in wheat.
Questar is the first naturally-derived fungicide brought to market by Corteva Agriscience; Inatreq is produced by fermentation of a naturally-occurring soil bacterium first discovered at Osaka University in Japan.
It’s been well received since Corteva launched it four years ago, but should be strategically integrated into more programmes as a critical circuit breaker to protect existing chemistry, Surgenor says.
It has no cross resistance to existing fungicides in the wheat market, and is highly efficacious, making it invaluable for resistance management strategies.
It has also been tested by Plant & Food Research since 2020 with Septoria showing no shifts in sensitivity to Questar (fenpicoxamid active).
It’s flexible in terms of application timing - up to T3 – although most applications will be at T1 or T2 which are the most important fungicide timings for Septoria control.
“We’re strongly recommending only one Questar application per season, which will help protect Questar from the development of resistance, and also make the most of this new MOA in slowing resistance to other fungicide groups,” Surgenor says.
“We very much want to be part of a responsible resistance management strategy for all fungicides for Septoria and other cereal disease control.”
Maintaining the efficacy of current fungicides requires careful management, which includes using different modes of action like Questar, applying the correct rates at the right time and growing Septoria tolerant wheat.