First report of white mould (Ramularia vallisumbrosae) on daffodils (Narcissus) in eastern England

Abstract

White mould (Ramularia vallisumbrosae) is a common and damaging foliar disease on daffodils (Narcissus cultivars) in the south-west of England that in some years causes epidemics in commercial Narcissus crops in Cornwall and the Isles of Scilly. Outside of this region the disease has previously been identified in Warwickshire, central England (Anonymous, 1929), on Anglesey, Wales (Baker, 1972), and in southern Scotland (Dennis & Foister, 1942). However, there appears to be no previous confirmation of the disease in eastern England (J.B. Briggs, E. Roberts, A. Inman, personal communication) where Narcissus has been grown on a large scale for over 100 years (Dobbs, 1983). White mould was identified in May 2001 on Narcissus cv. Carlton in Holbeach Marsh, Lincolnshire, in a crop being monitored for foliar diseases at c. 14-day intervals from January. Lesions occurred on leaves and stems and typically were pale brown, oval, c. 10–30 × 5–10 mm in size and contained numerous minute black, sclerotiumlike bodies. Microscopic examination revealed amerospores and phragmospores characteristic of R. vallisumbrosae (Moore, 1979). The disease was subsequently confirmed in crops of Narcissus cvs Spellbinder and Dutch Master on other farms in Lincolnshire (Holbeach Marsh and Kirton). Plant Health inspectors reported similar symptoms affecting various cultivars on several farms in the Spalding, Holbeach and Kirton area in 2000 and 2001 (E. Roberts, personal communication), however, the pathogen was not confirmed in these cases. In Cornwall, sporulating lesions of white mould are often seen in February before flowering, whereas in these newly reported instances in Lincolnshire, the lesions were seen after flowering, from May onwards. Although there is commercial interchange of bulbs between south-west and eastern England, the major bulbgrowing regions in the UK, the disease is not believed to be bulb–borne (Moore, 1979). In spring, no white mould was observed on plants grown from severely affected Narcissus cv. Carlton bulbs, harvested in July 1999 in Cornwall and grown under humid glasshouse conditions or in a polythene tunnel at Kirton (Lincolnshire) and Mepal (Cambridgeshire), respectively. This report suggests that there may now be an increased risk in eastern England, where c. 60% of UK Narcissus are grown, of outbreaks of this potentially epidemic disease with consequent early foliage die-down and associated reductions in bulb yield.