AHDB-funded research has provided information on the biology of the diseases as well as helping to produce guidelines for their effective management.
Smoulder is a fungal disease caused by Botryotinia narcissicola that in cool, wet seasons can spread through a crop, resulting in rapid premature leaf dieback and greatly reduced bulb yields. Initial symptoms are dark-brown/black leaf tips on emerging shoots in the spring.
White mould, which is caused by the fungus Ramularia vallisumbrosae, appears initially as small, slightly sunken grey-green or yellowish spots or streaks near the leaf tip. These increase in size to form yellowish-brown oval lesions.
Although cultivar choice greatly affects the risk of damaging white mould attacks, foliar fungicide sprays are the cornerstone of management for both diseases. Where a high risk of disease has been assessed from cultivar history, preventive foliar sprays have been shown to be beneficial.
Importantly, the fungicides that are used should be from at least two different fungicide groups to minimise the risk of selecting fungicide-resistant strains. Fungicide product choice and spray interval choice should be informed by monitoring the occurrence of foliar diseases.
More information, including example guideline fungicide programmes for management of narcissus leaf diseases, is available in new AHDB Horticulture fact sheet 30/16 "Control of narcissus leaf scorch, smoulder and white mould".
Narcissus growers' workshops will be held in Cornwall (17 May) and Lincolnshire (25 May). For more information and to book places, visit the AHDB Horticulture website.
For details on all AHDB Horticulture activity, see horticulture.ahdb.org.uk.