Cause Ditylenchus dipsaci. Infected bulbs are mostly responsible for carrying over infestations and establishing new ones. Stem nematodes infect aboveground plant parts and also are in soil. Can destroy a bulb stock in as little as 3 years. Although they can move short distances on their own, they can be spread passively by moving soil or water. Spread down rows in the direction of soil cultivation is common. The life cycle can be completed within the bulb in storage or in the field. Adults can lay up to 500 eggs, which go through 4 larval stages with the fourth stage being infective. Can also be a problem on tulip, hyacinth and phlox. Different races or biotypes occur with the tulip race highly pathogenic while the hyacinth race causes only minor lesions. The narcissus race can breed slowly in onions, beans, peas and strawberries.
Symptoms Foliage is distorted and off-color, yellow to brown depending on time of year. Sometimes, planting zones are severely stunted or rows have barren areas. Infected plants seldom produce satisfactory flowers, and blooming may be delayed or absent. Leaves have localized thickened areas called spikels. These are small, broken, roughened, swollen, yellow patches that usually occur along the leaf margin or the keel of the flower stalk. Infected bulbs have poor root development. Bulb cross-sections show brownish areas in the concentric rings of bulb tissue. Many infected bulbs soften, rot, and disintegrate in storage. Infected bulbs may dehydrate resulting in a survival structure exuding from around the base plate. These pinhead-sized blobs of off-white wool-like material will rehydrate with nematodes becoming active. Roots are not attacked.
Sampling Take soil samples before planting. If this nematode is suspected in an established plant, submit only the affected bulbs for testing.
Cultural control
- Discard heavily infected plants and bulbs. Remove healthy appear plants for up to 3 feet from infected plants.
- Harvest infected stocks early, before tops die completely.
- Disinfect used work areas, trays, cases, tools, and equipment by steam or hot water (185°F).
- Rotate 5 years out of bulbs and remove volunteer plants from previous bulb crops.
- Soak lightly infected stocks in properly designed equipment, when bulbs are fully dormant. Soak 4 hours in water at 110°F to 111°F. The treatment can distort flowers and leaves and spreads basal rot disease from infected to healthy bulbs; therefore, do not treat basal-rot-infected stock with hot water.
- Soon after digging bulbs, soak 4 hours in 111°F water.
- Bulbs allowed to cure require an additional 2-hour presoak at 75°F. Presoaking activates nematodes from the resting stage (when they are resistant to treatment) to a more susceptible stage.
Chemical control Soak clean bulbs for 4 hours in hot water plus formalin.
- Aldesan Microbiocide at 2 fl oz/gal of water and heat to 110°F to 111°F for 4 hours. Change dip tank water when it becomes discolored or when sediment is present. Dip dank wastewater may be applied to bulb fields when rain is not expected for 24 hours. Washington only. SLN WA-160001b. Formaldehyde Solution 37 is also registered with SLN WA-160001.
Reference Qiu, J., Westerdahl, B.B., Giraud, D. and Anderson, C.A. 1993. Evaluation of hot water treatments for management of Ditylenchus dipsaci and fungi in daffodil bulbs. Journal of nematology. 25:686-694.