Foliar-acting systemic seed treatments can contribute to pathogen resistance selection, when used in conjunction with a foliar spray programme based on the same mode of action.

Via the Chemicals Regulation Directorate (CRD), and AHDB Cereals & Oilseeds, this is a key conclusion of a 24-month project funded by Defra.

With efficacy against foliar cereal diseases, the ADAS-led work has confirmed current FRAC guidance that SDHI seed treatments, should count as one of the permitted applications made to a crop.

Existing models for predicting the development of fungicide resistance in the pathogen Zymoseptoria tritici (septoria leaf blotch) were extended to incorporate seed treatment effects.

To gauge the impact of each combination on a mode of action’s ability to control septoria and the rate of selection for resistance, systemic seed treatments, with efficacy against septoria, in combination with foliar sprays at a range of doses and timings (T1 and T2) were modelled.

Its maximum effective life when a single mode of action was used, before appearance of resistance, from two foliar sprays or a seed treatment and one foliar spray was equal.

Reduced the maximum effective life of the mode of action, adding a seed treatment to a two-foliar spray programme.

“If the pathogen population is exposed too frequently to a single mode of action, it will become less sensitive. We are now confident that if a seed treatment has foliar activity then, when it comes to resistance management, it should be considered as risky as a spray. These findings add weight to current resistance management guidance, which should be followed to protect SDHI chemistry and products. The results also provide valuable information to help develop guidelines for new modes of action as they are introduced,” said Dr Paul Gosling, who manages fungicide performance work at AHDB.

To provide and promote evidence-based, independent and practical information on resistance management, AHDB has worked with the Fungicides Resistance Action Group (FRAG-UK).

In the UK, there are currently no SDHI seed treatments with efficacy against foliar pathogens approved. Should any such seed treatments be approved, FRAG-UK would advise that these should count as one of the statutory limit of two SDHI applications to a crop. To keep records of seed treatments applied is become necessary.