Advice
RHS Help & Advice
Phlox eelworm (Ditylenchus dipsaci)
Plants affected
Perennial, alpine and annual phlox. Other potential host plants are listed below.
Symptoms
Stems are stunted and swollen, with leaves at the shoot tips much reduced in width. Such shoots die back early, having failed to flower. Cold weather in the spring or aphid infestations can also cause distorted foliage, but this is usually less severe and there is no abnormal thickening of the stems or early dieback. On alpine-type phlox there can be extensive dieback of the shoots without any obvious signs of distorted growth.
Cause
Microscopic eelworms or nematodes living within the stems and foliage are responsible for the damage. This pest overwinters on the plant inside the basal buds.
Control
None of the pesticides available to home gardeners will control eelworms.
Bin or burn affected plants. Avoid replanting the site with phlox and other susceptible plants for at least 12 months. Host plants include Aubrieta, Campanula persicifolia, Dianthus barbatus (sweet William), Gladiolus, Gypsophila, Helenium, Oenothera spp (evening primrose), Primula species, and Solidago (golden rod). Some weeds, such as shepherd's purse, hairy bitter cress, broad-leaved willow herb, mayweed and procumbent speedwell, are also potential host plants. As the eelworm only infests the leaves and stems of phlox, new healthy plants can be propagated from root cuttings taken in autumn or spring.