| Disease (causal agent) | Symptoms | Survival of pathogen and effect of environment | Comments on control | |
|---|---|---|---|---|
| Basal rot (Fusarium oxysporum f. sp. narcissii) |
Infected plants are stunted with distorted and yellow leaves, and usually die. The basal plate is decayed and reddish brown in color. The white to pinkish fungus is sometimes seen at the base between the scales. Eventually the bulb rots. | Fungus survives as chlamydospores in soil for long periods. Short rotations are not effective. Disease is favored by warm soils and is limited below 55°F; disease is favored by high levels of nitrogen fertilization. Potassium fertilizer may decrease disease sensitivity. | Avoid excessive fertilization. Dig up bulbs in diseased areas as soon as possible. Store bulbs below 64°F. Dip bulbs in thiabendazole as soon as possible after digging. Hot water treatment (see stem and bulb nematode) is also effective in reducing the disease. Rotate out of narcissus for at least 3 years. Plant when soil is cool. | |
| Susceptibility of narcissus cultivars to basal rot: | ||||
| Susceptible: Carlton, Golden Harvest | ||||
| Moderately susceptible: Toorak Gold, Dutch Master, Hollywood | ||||
| Moderately resistant: Malvern City, Rijinveld's Early Sensation, White Lion, Soleil d'Or, Dulcimer | ||||
| Resistant: St. Keverne | ||||
| Crown rot or Southern blight (Sclerotium rolfsii) |
A bulb rot that is at first wet and later becomes dry and woody. A white fungus mat and small (0.03–0.125 inch), round, tan to brown sclerotia occur on decaying bulbs and in surrounding soil. | Disease is favored by warm weather. Fungus survives in soil for long periods (10 years). Fungus has a wide host range. Can be spread by infected bulbs. | Avoid infested fields for 4 years or longer. Deep plowing is sometimes practiced to bury sclerotia. Treat bulbs in hot water. (See stem and bulb nematode.) PCNB applied in the furrow at planting can be effective. | |
| Fire (Botryotinia polyblastis) |
Water-soaked areas on petals that become brown and wither. Flowers are attacked first, and later the foliage. Foliage spots are small, elliptical, tan and usually near the tips. Yellow streaking follows the leaf spots. | Fungus survives as sclerotia in leaf debris. Sclerotia germinate in spring to produce fruiting bodies (apothecia), which produce airborne spores (ascospores). Conidia, which are also airborne, cause secondary spread. The disease is favored by mild, humid conditions. | Remove flowers before fungus produces apothecia in March/April. Protect flowers and foliage with a fungicide. | |
| Scorch (Stagonospora curtsii) |
Yellow to brown lesions at leaf tips. Elongate reddish brown leaf spots. Small black pycnidia form in necrotic areas. | The fungus survives in the neck and between scales. Disease is favored by mild, moist conditions. Spores are spread in splashing water. The fungus infects members of the Amaryllidaceae. | Treat bulbs with hot water. Protect plants in the field with fungicides. Make first application as leaves emerge. | |
| Smoulder (Botrytis narcissicola) |
A dark brown lesion first appears on leaf tips. Infected leaves may curl when infection occurs on inner edge. Masses of fuzzy gray spores (conidia) and small black sclerotia form on diseased tissues, especially near soil. | Fungus survives in infected bulbs and as sclerotia in soil. Conidia are airborne. Favored by cool, wet weather. | Rotate with other crops. Dig bulbs early. Dip bulbs in suitable fungicide such as thiabendazole. If disease is severe in field, spray with iprodione, fenhexamid, or thiophanate-methyl. | |
| Stem and bulb nematode** (Ditylenchus dipsaci) |
Leaves are stunted and distorted, and often swollen and thickened near the base. Yellow or brown swellings occur in leaf centers and margins. Severely infected bulbs are unproductive and may rot. | Nematodes survive in infected bulbs and in bulb debris in fields for about 3 years. Optimum temperature for infection and reproduction is 50° to 60°F. (Little activity occurs when soil temperatures are lower than 50°F and greater than 68°F.) Nematodes are spread by irrigation water and equipment. They also survive in weed hosts and can survive desiccation. | Remove infected plants and surrounding plants from the field. Clean equipment after use in diseased fields. Treat bulbs in hot water. Store bulbs at 60° to 64°F before treatment to reduce heat injury. Presoak bulbs 2 to 3 hours or overnight in water plus a wetting agent at 75°F. Increase temperature in morning to 109°F. Once the temperature of the treatment solution reaches 109°F, maintain a constant temperature of 109° to 111°F for 3 to 4 hours. Cool and dry bulbs immediately. CAUTION: Hot water treatment may injure bulbs causing stunting and flower blast or deformation. Obtain expert advice before large-scale treatment. | |
| White mold (Ramularia vallisumbrosae) |
Small, sunken, grey or yellow spots on leaves and green parts. Spots enlarge and darken to a yellow- brown with yellow margins. Masses of white, powdery spores (conidia) occur on leaves under moist conditions. Small, dark sclerotia are produced in older infected tissues. | Fungus survives as sclerotia in dead leaves and on bulbs. Sclerotia germinate to produce conidia as leaves emerge. Disease is favored by warm, moist conditions. | Do not replant for 1 year in fields where the disease has occurred. Protect foliage with mancozeb. Copper fungicides are also helpful. | |
| Virus or viruslike disease | Symptoms | Host range and natural spread | Comments on control | |
| White streak (Narcissus white streak virus) |
Narrow, dark green to purple streaks, which later become white to yellow-white, appear in leaves and flower stalk after flowering. Bulb size and yields are reduced by premature senescence. | Narcissus is the only host of the virus, which is transmitted by aphids. Symptoms do not occur until air temperatures exceed 64°F. | Eliminate infected plants. Control aphids. | |
| Yellow stripe (Narcissus yellow stripe virus) |
Conspicuous light green to yellow streaks and mottling of leaves and flower stalk, which occurs shortly after emergence. Sometimes leaves are distorted and a color-break of flowers occurs. Bulb yields are reduced. | The virus infects only narcissus and is spread by aphids. Symptoms appear early in growing season. | Eliminate infected plants. Control aphids. | |
| Equipment that has come into contact with diseased bulbs should be thoroughly cleaned by heat treatment. | ||||
| Narcissus may become infected by a number of other viruses; some produce inconspicuous symptoms. Narcissus is also susceptible to Stromatinia dry rot (Stromatinia narcissi), black slime (Sclerotinia bulborum), soft rot (Rhizopus stolonifer), bacterial streak (Pseudomonas sp.) and root lesion nematode** (Pratylenchus penetrans). | ||||
| ** For additional information, see section on Nematodes. |