Ditylenchus dipsaci Stem and bulb nematode Damage to vegetables. Ditylenchus dipsaci attacks the bulbs and cloves of onions, garlic, and ornamentals. Hosts include onion, garlic, carrots, peas, potatoes, strawberry, apples and peaches.  Biology.  Stem and bulb nematodes are commonly classified as migratory endoparasites, completing their life cycles within the tissues of bulbs, stem, and leaves (but rarely in roots). They penetrate the base of stems or the bulb scales and feed on cell juices, injecting toxic substances which produce necroses and distortion of the plant tissues.  An economically important feature of the stem and bulb nematode is its ability to survive repeated desiccation or drying.  Dry nematodes can be reactivated by moisture when infested material is replanted or when a new crop is planted in soil containing old, infested material. Ecology.  Stem and bulb nematodes are widely distributed, especially in temperate regions. Symptoms.  Ditylenchus dipsaci causes twisting, distortion, and discoloration of stems and foliage of ornamentals, and  distorted and cracked bulbs. Plants can be stunted, fail to bloom, and die prematurely.  In strawberries, leaves are small and distorted, and the foliage dries out and falls off.  Damage to other crops. D. dipsaci also attacks field crops, including alfalfa, oats, and clover, in which young buds are attacked, preventing normal stem elongation. Control.  Cutural control (preventing introduction and/or dispersal of the nematode) is recommended. Links and References.  Stem nematode in phlox.   Nematode management in onions.