Assessing the resistance risks associated with systemic fungicide seed treatments and the effectiveness of risk modifiers

Project number
Lead scientist
Neil Paveley
CRD/Defra, Rothamsted Research
Start Date
End date
HGCA funding

The challenge

Systemic seed treatments based on the new generation of SDHI fungicides are being developed for use on cereals, targeting foliar disease control as well as seed-borne diseases. These treatments have the potential to improve disease control and raise yields. However, disease control causes selection for fungicide resistance and the strength of selection determines how rapidly resistant strains dominate pathogen populations and erode control. Hence, there are potential risks associated with the same mode of action being used for both seed and foliar treatments.

The crop protection industry advocate that a foliar-acting SDHI seed treatment need not be counted as one of the restricted number of SDHI applications permitted per crop, provided certain resistance risk ‘modifiers’ are in place. But there is insufficient evidence to judge whether this guidance is appropriate to the degree of resistance risk or whether the proposed modifiers are likely to be effective. A precautionary approach may be used in the absence of evidence but may be unnecessary.

The project

- Quantify the effect of foliar-acting seed treatments on selection for fungicide resistance.

- Relate effective product life to disease control through its effects on resistance selection, so that the resistance risk associated with future seed treatments can be assessed using efficacy data.

- Test the extent to which risk ‘modifiers’ (anti-resistance strategies) are effective for combined seed-treatment and foliar-fungicide programmes.

Field experiments will measure selection for fungicide insensitive pathogen strains in the presence/absence of foliar-acting seed treatments, and with/without risk modifiers.

Mathematical models of fungicide resistance, developed and tested previously in CRD/Defra funded work, will be extended to incorporate seed treatment effects and validated against the experimental data. The models will then be used to: (i) explore the resistance effects of a wider range of seed treatment foliar fungicide combinations than can be tested experimentally, (ii) quantify the rate of selection for fungicide insensitivity, and the resulting effect on effective lives for modes of action, and (iii) interpret the findings for a range of pathogens.

The benefits

Quantification of the fungicide resistance risk associated with the use of foliar-acting seed treatments and the effectiveness of ‘risk modifiers’ to ameliorate resistance risks will enable more sustainable use of fungicides, extending their effective lifetimes.


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