UK: Narcissus leaf scorch, smoulder and white mould
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 which 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 is caused by the fungus Ramularia vallisumbrosae and 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 choice of cultivar greatly affects the risk of damaging attack from white mould, foliar sprays of fungicides are the cornerstone of management for both diseases.
Where a high risk of disease risk has been assessed from cultivar history, preventative foliar sprays have been shown to be beneficial.
Importantly, fungicides 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 are available in a new AHDB Horticulture factsheet 30/16 ‘Control of narcissus leaf scorch, smoulder and white mould’.
Two narcissus growers’ workshops will be held in May 2017 in Cornwall (17) and Lincolnshire (25).