Potato growers can manage the increasing incidence of blight resistance with effective fungicide mixing strategies, say experts.
Speaking at the Potato Science Live events this spring, Syngenta technical manager Andy Cunningham said a mandipropamid mixing strategy was helping growers in Denmark to control resistant blight.
Incidents of blight strain EU 43 have fallen from over 70% of recorded cases in 2022 to fewer than 20% last season. As a result, recommendations for the use of Revus in Denmark have increased by over 60% for this season.
“UK growers are in a far more fortunate position,” said Mr Cunningham.
Options available
“The EU 43 strain has never been sampled in blight monitoring
programmes, and they have many more options available for mix partners that will enable them to reliably use Revus in this season’s programmes.”
Revus has consistently proven the most potent blight fungicide for protection during the most important early and mid-canopy phase – with news that OXTP has now also been compromised with resistance in the European blight population.
To ensure Revus retains its full efficacy – and to avoid selecting for any resistant strains that do arrive in the UK – Mr Cunningham says it should always be mixed with a complementary blight fungicide with an alternative mode of action.
The partner fungicide must give protection equal in duration to Revus in the blight programme schedule. Suitable partners this season include mancozeb, fluazinam, propamocarb and cyazofamid – and leading contender amisulbrom.
Kick-back activity
“There is potentially a role for cymoxanil to give kick-back activity, in the event of a weather delayed application, but our Eurofins blight trials indicated it may not give the desired duration of protection – so intervals would have to be tightened.”
Mixing fungicides was proven to break resistance, said Mr Cunningham. Even a season-long programme of fluazinam – mixed with a range of partners – maintained full or high control in a trial crop inoculated and infected with resistant strain EU 37.
“With appropriate mixing strategies we can both minimise the risk of resistant blight strains established in the UK, and still get beneficial effects from compromised chemistry should it occur.
“Potato growers and agronomists need to take a responsible approach to planning this season’s blight strategy, and still take full advantage of the benefits of Revus for highly effective foliar blight control.”
