Basal rot of Narcissus (daffodils) is a fungal infection which decays the base of the bulb, often during winter storage. If infected bulbs are planted, the resulting growth is yellow and may not flower.
What is daffodil basal rot?
Basal rot is one of the most serious diseases of daffodils and is caused by the soil-borne fungus Fusarium oxysporum f. sp. narcissi. The fungus enters the bulb initially by rotting roots, or directly through weaknesses in the base. Look for symptoms whenever the growing bulbs fail and on lifted, stored bulbs.
The disease is very difficult to detect in its early stages. As the brown, spreading rot develops, the bulb feels slightly soft.
You may see the following symptoms:
- On bulbs in storage: A pinkish-white fungus may be visible between affected scales and on the basal plate. Eventually the bulb rots completely and in storage appears mummified
- If infected bulbs are planted: Foliage may yellow prematurely and the bulb may not flower
- Infection may also occur through the neck of the bulb after flowering has finished, causing neck rot
The fungus Fusarium oxysporum is very common in the soil, where the majority of the population lives as a saprophyte (a harmless organism that feeds by decaying dead organic matter). However it also has a large number of pathogenic strains, which are able to infect different plants.
Fusarium oxysporum f. sp. narcissi only infects Narcissus. It is found in the soil, even where Narcissus have not been grown previously, and can be found on the surface of bulbs even when these are apparently healthy. Infections occur through wounds or weaknesses, such as the point at which young roots grow out into the soil from the base of the bulb.
Neck rot occurs when infection enters around the neck, often after flowering has finished.
Infection is sometimes associated with attack by the stem nematode (eelworm) Ditylenchus dipsaci, but the two problems may also occur independently.