The declaration of another official race of Bremia lettuce Downy mildew that is now endemic across the UK and Europe, further highlights the risk of evolving strains of disease and reinforces the need for growers’ action to avoid serious losses, warns Syngenta Salads specialist, George Hallam.
The International Bremia Evaluation Board (IBEB) nominated race BL:32 as a new official race, citing its widespread presence across northern Europe and, more recently, its continued spread into Spain and Portugal too.
However, the Board also highlighted that the majority of Bremia isolates identified, over 80%, were of diverse strains of the disease that were locally important and potentially damaging, but unlike previously nominated strains had spread less fast – which it attributed largely to the successful introduction of resistance genes in lettuce varieties.
George Hallam pointed out that the current Syngenta lettuce varieties already possessed the necessary genes for resistance to the newly nominated BL:32, apart from one iceberg variety, Challenge.
“Furthermore, the broad-base resistance bred into today’s Syngenta baby leaf, iceberg and speciality lines provides growers across Europe with valuable insurance against locally developing strains of Bremia,” he added. “Our breeders’ aim is to stay one step ahead of developing Bremia races.”
To further prevent the development of new Downy mildew races, George reinforced the IBEB emphasis on the importance of chemical control and field hygiene measures, alongside the genetic resistance. The Board advocated the importance of fungicide programmes, especially at the early growth stages, along with the removal of crop debris and diseased plants from the field.
“Syngenta trials and growers’ experience has repeatedly demonstrated the effectiveness of Revus for disease protection,” reported George. “In high risk cool, wet conditions a robust seven-day programme remains essential. The use of a range of different modes of actions in the programme to compliant Revus, such as Fubol Gold and Amistar, in mixture with mancozeb, is essential to maintain fungicide effectiveness.
“But good genetic natural resistance is an extremely valuable extra insurance protection for crop health if weather conditions disrupt the spray schedule, or through high disease pressure situations,” he advocated. “It can also help to prevent disease build-up prior to harvest, when fungicide programmes end for pre- harvest interval compliance, and give greater flexibility in harvesting clean leaves with longer shelf-life.”
New Syngenta salad introductions for 2015, include innovative baby leaf varieties, along with new speciality lettuces, will include natural resistance to the full spectrum of nominated Bremia races.
For more information on the role of the IBEB visit http://www.worldseed.org/isf/ibeb.html or contact info@plantum.nl
For UK specific agronomy, seeds and product information go to www.syngenta.co.uk