31-07-2025
Combatting potato blight fungicide resistance key focus for researchers
The continuing work of Teagasc scientists to successfully confront the challenge of potato blight has been highlighted.
This work is taking place against the backdrop of the fast-evolving blight populations that now impact on Irish potato crops.
Details of this research input are contained in the recently published Teagasc Research Impact Highlights in 2024.
In late autumn 2023, a single sample of Phytophthora infestans with resistance to the carboxylic acid amide group of fungicides was detected in Ireland.
Currently, the control of potato late blight caused by P. infestans is almost exclusively reliant on the application of fungicides. This highlights the immediate and significant threat the detection of this strain posed to the Irish potato industry.
To prevent such devastating impacts, it is essential to be able to rapidly detect this strain, devise control strategies to prevent its spread, and effectively communicate this to the industry.
The Teagasc report outlined how a coordinated approach was taken between crops researchers and specialists to develop detection tools, and devise and disseminate field control strategies.
To detect resistance, the team developed a digital droplet polymerase chain reaction (PCR) capable of detecting P. infestans and associated fungicide resistance in a variety of matrices including potato leaves, FTA preservation cards, and spore samples.
This allowed for the rapid and extremely sensitive detection of resistance.
In parallel, control strategies were devised which ensured both the mixing and alternation of fungicides at each application, guaranteeing field control whilst limiting potential selection for the resistant strain.
These strategies were communicated to the industry throughout the season via dedicated workshops, crop walks, and a trials tour.
Whilst the strain was again detected in 2024, its impact on late blight control has been contained.
Potato growers attending a recent Teagasc farm walk in Co. Meath were told that the threat of blight remains very real.
And this despite a continuing spell of dry weather, during which humidity levels remains very low.
Testing carried out last year confirmed that 36A2 was the main strain of blight circulating in Ireland at that time, a strain that is not strongly associated with mutations that bring about resistance to specific fungicide chemistries.
But according to Teagasc plant disease specialist, Dr. Steven Kildea, potato growers should not be lulled into any form of false security.
He explained: 'Last year's survey work tells us one fundamental thing: 36A2 is a very active form of blight. It has imposed itself relative to other blight strains known to be in Ireland.
'This means that A36 has the potential to create serious damage within Irish potato crops if farmers do not take the required preventative steps.'
As was the case last year, Teagasc agronomists have compiled a comprehensive blight spraying programme for 2025.
