Independent trials, carried out in Lincolnshire last season by researchers at Agrochemex, identified extra levels of curative control of ringspot with an Amistar Top programme compared to other strobilurin-based fungicides.
Syngenta technical manager Jon Ogborn said that growers have been tank-mixing Amistar (azoxystrobin) with Plover (difenoconazole) for some years, but the new optimised formulation of the two active ingredients in Amistar Top has proven extremely effective on a broad spectrum of brassica diseases, especially ringspot, powdery mildew and white blister.
He added: "Furthermore, with the intense pressure put on brassica growers to supply exceptional quality at the lowest-possible price, the better value offered by the pre-formulated product is helping to minimise input costs.
"The trials demonstrated to growers that they can successfully now alternate Amistar Top applications with straight Plover to get the highest levels of control under difficult conditions.
"The combination provides extra curative activity to effectively control diseases that threaten the marketable quality of brassica crops close to harvest. This is combined with excellent crop safety."
The trials in Lincolnshire found that an Amistar Top/Plover programme controlled 98 per cent of ringspot in a crop of the cabbage variety Canada, while a tebuconazole + trifloxystrobin/Plover alternation achieved just a 75 per cent reduction in disease level.
In another trial, with Alaska cabbage showing even higher levels of disease incidence (28 per cent in untreated plots), the Amistar Top/Plover achieved nearly 90 per cent control, when pyraclostrobin + boscalid/Plover gave less than 70 per cent reduction in disease. The applications were made at four- to six-week intervals through October, November and December.
John Keer of Agrochemex said ringspot is the most damaging brassica disease in the prime south Lincolnshire region, and can prove especially severe in susceptible savoy cabbage varieties.
"Curative activity is especially important for the control of ringspot at the end of the season, when disease pressure is highest and the incubation period may be prolonged in cooler conditions.
"Amistar Top has a robust rate of difenoconazole for optimum curative action and good protectant disease control."
Syngenta speciality crops manager Bruce McKenzie said Amistar Top has a greening effect that ensures optimal retention of green leaf for visually attractive brassicas. It has been observed that the healthier leaves are also less susceptible to Xanthomonas infection. Better disease control in the field also makes harvesting quicker and more efficient with limited labour available - requiring less selection, trimming and rejection.