Increased threat of SDHI fungicide-resistant septoria in UK

Experts have warned that SDHI fungicides are now at a medium to high risk of developing resistance in cereals.

A statement has been issued by the Fungicide Resistance Action Group-UK (Frag-UK), an organisation of academics and agrochemical firms which works to prevent loss of fungicide efficacy.

It comes after news that strains of septoria with target-site resistance to SDHIs have been found in Ireland.

It stresses the importance of strictly adhering to resistance management guidelines for cereal fungicide programmes.

Last week Irish researchers discovered that samples of some septoria strains could survive 100 times the concentration of SDHI fungicides, compared with the most insensitive strains found previously.

See also: SDHI fungicide-resistant septoria found in Irish fields

This is the first time scientists have detected septoria mutations with target-site resistance to the key fungicide group – which includes actives such as bixafen (in Aviator) and fluxapyroxad (in Adexar) – in the field.

With the efficacy of other fungicides growers use to fight the yield-sapping disease already fading, this is viewed as a worrying development.

The Frag-UK statement says the industry “collectively and individually can and must act to steward these products.”

It adds that the SDHI resistance risk can be “modified and reduced by either mixing or alternating with fungicides with an alternative mode of action, or by reducing the number of applications or dose of the fungicide.”

AHDB research manager Dr Paul Gosling said: “Our trials show that SDHIs remain the most active chemistry against septoria when applied in protectant situations.

“However the new information on SDHI sensitivity once again shows why it is critical to adopt best resistance management practices.”

At this year’s AHDB Cereals and Oilseeds Agronomists’ Conference, Adas senior research scientist Jonathan Blake told delegates that the findings in Ireland reinforced the need for SDHI stewardship. 

Fungicide resistance management guidelines

  • Limit the number of fungicide applications to two SDHI fungicide- containing sprays
  • Always use SDHI fungicides in mixture with at least one fungicide from an alternative mode of action group which has comparable efficacy against the target pathogen(s)
  • Tank mixing two SDHI fungicides is not an anti-resistance strategy. In any tank mix the SDHI should be applied in a balanced mixture with at least one fungicide with comparable efficacy

Read the full Frag-UK statement (PDF) on SDHI fungicides and resistance risk in cereals.

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