Bayer hopes to lay waste to early blight in potatoes, with its new fungicide, Caligula.

It contains 125g/L fluopyram and 125g/L prothioconazole in a suspo-emulsion (SE) formulation and has demonstrated a level of yield protection against early blight in trials that looks set to secure it one of the highest ratings of any product on the Euroblight early blight league table.

Available on a limited release in 2020, Caligula will be fully available in 2021. News of a product with strong activity against early blight will likely be welcomed by growers given the uncertain regulatory future facing mancozeb.

“Across Europe, early blight is presenting an increasing threat to potato crops. It has the potential to inflict severe damage to yields with losses in the published literature ranging from 5 to 78% depending on the extent of canopy defoliation. Caligula has demonstrated strong protection against this disease, up to 84% depending on the other products in the programme, and incidental control of sclerotinia,” said Lizzie Carr-Archer, Bayer's root products campaign manager.

The increasing threat posed by early blight has been highlighted recently by news of a novel genotype of alternaria solani, the more significant species of the disease to threaten crops. This was found to be more aggressive than wild relatives and less well controlled by products belonging to the quinone outside inhibitor (QoI) group of fungicides.

Isolates with reduced sensitivity to pyraclostrobin, azoxystrobin and famoxadone were first detected by researchers in Germany and more recently, research elsewhere in Europe has identified reduced sensitivity to some SDHI active substances, namely boscalid.

“Caligula offers protection against all forms of the disease including the less sensitive isolates and with two products each belonging to different mode of action groups, it has in-built resistance management,” said Mrs Carr-Archer.

Aside from reduced sensitivity to some fungicides, the reasons for the increased prevalence of early blight are thought to include the introduction of more susceptible varieties and more favourable weather in the early spring supporting sporulation.

“Data on the incidence of early blight is more limited than that for the late blight, but as every agronomist it is usually present in most seasons. The emergence of strains less sensitive to some products and the possible loss of products known to be effective at controlling it means it is likely to be a greater problem in the future,” she added.

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

“When 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, while Amistar delivered 68% control and Narita 80%. The average extra yield delivered by Caligula from this higher level of control was 3% over the other treatments,” pointed out Mrs Carr-Archer.

“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,” she added.

For best yield protection, Caligula should be applied in programme with other modes of action. Bayer recommend it be applied in a preventative programme with the first application made during flowering (BBCH 61-69), typically at some time in July, and then the second application 10-14 days later, depending on disease pressure.

"The final application should be made only after a product with another mode of action has been applied,” added Mrs Carr-Archer.