Several viruses cause disease in daffodils. Narcissus yellow stripe virus (NYSV) is the most common.
Symptoms
Symptoms are most easily seen in February and March. NYSV
causes yellow streaks on the leaves and flower stems, and
flower ‘breaking’ - streaking or mottling of the
petals. Other viruses cause white streaking, distortion and
curling of leaves and stunted growth.
Biology
NYSV and some other viruses are spread by aphids. Some viruses are spread by soil-inhabiting eelworms, or by rough handling of plants, which spreads the infected sap.
Control
Buy bulbs from a reputable supplier to ensure the disease is not introduced in infected bulbs. There are no cures for virus diseases and diseased plants should be removed and destroyed to limit spread of the disease to neighbouring plants in the garden.