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Caligula, a new fungicide from Bayer containing 125g/L fluopyram and 125g/L prothioconazole in a suspo-emulsion (SE) formulation, has demonstrated a level of protection against early blight (Alternaria spp.) that is set to secure it one of the highest ratings of any product on the Euroblight early blight league table.

News of a product with strong activity will likely be welcomed by growers given the withdrawal of mancozeb after the 2021 season.

While late blight (Phytophthora infestans) is regarded as the bigger threat to crops, early blight is a disease of increasing significance in the UK. The reasons for its increased prevalence are not fully understood, but it is thought to be due to a combination of factors including the introduction of more susceptible varieties, the spread of A. solani isolates less sensitive to QoI fungicides, and more favourable weather in the early spring supporting sporulation.

The damage Alternaria inflicts on crops varies according to the season – measured losses in unprotected crops vary enormously from 5 to 78% – depending on the extent of canopy defoliation.

In registration trials spanning six seasons between 2013 and 2018, Caligula was compared directly with programmes featuring Narita (difenoconazole), Amistar (azoxystrobin), or Signum (boscalid + pyraclostrobin). 

Applied in a preventative sequence at 14-day intervals, Caligula delivered 84% control of early blight in the susceptible phase of the crop. Comparable treatments with Signum achieved 47% of control, whereas Amistar delivered 68% control and Narita 80%. Caligula demonstrated this higher-level control with an average yield benefit of 3% over all other treatments.

Trials also considered its incidental control of Sclerotinia compared with Signum (fluazinam). A preventative sequence of Caligula treatments delivered a 30% reduction of stem infection by Sclerotinia, whereas a similar sequence with Shirlan resulted in an 11% reduction. The Caligula sequence resulted in significantly lower incidence of sclerotia within stems (94% control, recorded in one trial), compared with a 40% reduction for fluazinam.

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