Potato Review

36 POTATO REVIEW MARCH/APRIL 2021 CONFERENCE REPORT “ e two species are virtually indistinguishable in the eld, but A. solani is the more damaging as it produces bigger lesions and can infect crops without rst needing an entry point caused by an unrelated event. Most varieties have good tolerance to A. solani, but Markies, Ramos, Lady Christl and Aveka have been found to su er problems, other varieties might be a ected too.” As with programmes for late blight (Phytophthora infestans), interventions should be timed before the disease pressure begins to build. Achieving this in practice is often di cult as predicting the onset of disease is notoriously hard. “Developing more accurate decision support systems will be essential to promoting protection against both early and late blight. e early systems lack the capacity to consider crop development, crop stress, and the presence of other diseases which can hinder protection practices, so further work is needed,” said Bert. Production practices, especially nutrient availability, have been found to have an impact on disease development, but more work is needed to fully understand this relationship. “We have seen that crop health is a factor in disease onset, especially where nitrogen availability is restricted. is can be through low application rate or low soil reserves. is is another reason to favour split applications to keep promote canopy growth and delay senescence, but beware that too much, too late can impair tuber quality,” he said. Caligula launched to battle Alternaria Caligula, a new fungicide from Bayer containing 125g/L uopyram and 125g/L prothioconazole in a suspo-emulsion (SE) formulation, was launched by Bayer at the conference. In trials, Caligula 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 signi cance in the UK,” said Grant Reid, Bayer Commercial Technical Manager for central Scotland. e reasons for its increased prevalence are not fully understood, but it is thought to be down 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. e damage Alternaria in icts on crops varies according to the season – in the published research, 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),” said Grant. 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%. e average extra yield from Caligula over all other treatments, delivered by this higher-level control, was 3%. “Trials also considered its incidental control of Sclerotinia compared with Signum ( uazinam). 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. e Caligula sequence resulted in signi cantly lower incidence of sclerotia within stems (94% control, recorded in one trial), compared with a 40% reduction for uazinam,” he added. “Early blight is a disease of increasing significance in the UK.” Grant Reid, Commercial Technical Manager for central Scotland “It is how the elements of a programme are combined that defines the chances of success.” Jack Hill, Roots and Horticulture Commercial Manager Amy King, Market Development Representative for roots and horticulture. Bert Evenhuis of Wageningen University & Research. Jack Hill, Roots and Horticulture Commercial Manager. Grant Reid, Commercial Technical Manager for central Scotland.