How two changes can triple the lifespan of SDHI fungicides
© GNP Winter wheat growers are being advised to utilise the four main groups of fungicides to help fight any build-up of disease resistance and prolong the life of newer products.
This advice is based on new Adas modelling work that shows replacing a SDHI fungicide with a picolinamide at the T1 or T2 timing and adding a multisite in the fungicide programme will treble the lifespan of SDHIs.
For septoria in wheat, farmers are heavily reliant on azole and SDHI chemistry to manage the disease.
See also: Two new generation SDHI fungicides at risk of cross-resistance
However, there is a risk of resistance build up with the repeated use of an SDHI/azole. Over the years, there has been a steady decline in efficacy of both groups.
Back in December 2025, experts at the AHDB Agronomists conference also warned that there were early signs that two new-generation SDHI fungicides – Miravis Plus (pydiflumetofen) and Vimoy (isoflucypram), can develop cross-resistance.
Laboratory analysis, funded by AHDB, found isolates that were less sensitive to Miravis Plus and Vimoy following solo SDHI treatments.
Protecting newer SDHI fungicides
Septoria in wheat © Blackthorn Arable
So how can farmers protect these newer SDHI fungicides?
Adas principal consultant for crop disease management Michael Grimmer points to Fungicide Resistance Action Group (Frag-UK) resistance management guidance.
It lists a number of actions including integrated strategies, such as varietal choice and controlling volunteers, which may harbour disease (see panel).
One key area is the use of effective fungicides with different modes of action in mixtures or as alternate sprays.
To investigate how making changes to a fungicide programme will affect resistance build-up, Adas used a model to track resistance development in wheat in a number of different scenarios.
Michael says modelling is a valuable tool as researchers can test many situations, such as different product combinations and doses.
The latest AHDB fungicide dose-response curve data was used to determine effectiveness, and the model predictions have been validated in field trials.
The starting point was a typical disease programme based on using an SDHI fungicide plus azole mixture at both the T1 and T2 timings.
He looked at three scenarios, replacing one of the SDHIs with a different mode of action (fenpicoxamid) along with the addition of a multisite at the T1 and T2 timings.
SDHI fungicide plus azole mixture at T1 and T2 timings |
||
|
|
T1 |
T2 |
|
Scenario 1 |
1.12 litres/ha Vimoy + azole |
1.46 litres/ha Miravis + azole |
|
Scenario 2 |
1.2 litres/ha Univoq |
1.46 litres/ha Miravis + azole |
|
Scenario 3 |
1.12 litres/ha Vimoy + azole |
1.2 litres/ha Univoq |
|
Source: Adas |
||
When replacing Vimoy (isoflucypram) with Univoq (fenpicoxamid + prothioconazole) at the T1, the model predicted a 0.8 times increase in the lifespan of the SDHI.
The effect was greater when replacing Miravis (pydiflumetofen) at T2, effectively doubling its lifespan.
Michael says the reason is because Miravis is more effective than Vimoy at controlling septoria, so disease resistance built more quickly in the model simulations.
Adding the multisite folpet at both T1 and T2 gave a 50% longer lifespan, thereby tripling the life of the SDHI.
In conclusion, Michael says replacing one SDHI with Univoq reduces that selection pressure and helps extend the effective life of SDHIs.
Adding a multisite further strengthens resistance management and underlines the value of diversified fungicide strategies.
Four main groups of fungicide for septoria control |
|
|
Group |
Fungicide |
|
Single site |
Azoles including prothioconazole and mefentrifluconazole |
|
Single site |
SDHIs including pydiflumetofen and isoflucypram |
|
Single site |
Picolinamide fenpicoxamid |
|
Multisite |
Folpet |
Good resistance management limits the level of exposure of the pathogen to the fungicide
Use integrated pest management (IPM) measures to control disease
- Use disease-free seed lots, good hygiene through disposal of crop debris
- Control volunteers which may harbour disease
- Select varieties exhibiting resistance to diseases known to be prevalent in your area
- Avoid growing large areas of any one variety, particularly in areas of high disease risk
Use fungicides according to need
- Only use fungicides in situations where the risk or presence of disease warrants treatment
-
Use a dose that will give effective disease control
Use fungicide application strategies that slow resistance development
- Use effective fungicides with different modes of action in mixtures or as alternate sprays
- Avoid repeated applications of the same product or mode of action
Corteva’s view
SDHI plus azole chemistry at the T1 and T2 timings have been the backbone of fungicide programmes for the last decade.
As a result of this, there are strains of septoria that are less sensitive to azoles and SDHI chemistry.
As these populations already exist, Corteva Agriscience’s fungicide marketing manager Mike Ashworth warns that as the new SDHI fungicides arrive, they will select further being the same mode of action.
The newer SDHIs are also much stronger than previous generations and this “moves the selection pressure up a notch.”
He acknowledges that there has been no failure of control with SDHI and azole fungicides.
“However, we have seen a long-term reduction of efficacy and there will come a time at which effective control will be lost,” he warns.
From a resistance point of view, there is a need for all the other modes of action to remain effective.
