Eelworms of a large variety of species attack a wide range of plants, especially chrysanthemums, onions, strawberries, potatoes and tulips. The species are specific to the host plant in most cases, or a narrow range of hosts.
The tiny, microscopic worms get into the leaf, stem and root tissue of plants and feed in the sap, the plants often taking on a swollen or ‘bloated’ look, especially bulbous plants. Affected plants fail to flower, crop poorly and should be lifted and destroyed. Eelworms often spread virus diseases.
Potato cyst eelworm is the most common and troublesome garden pest. The eelworms feed on the roots and attach themselves. The pregnant females swell to form white or yellow spheres, just visible to the naked eye, or with a hand lens, standing out from affected potato roots. The symptoms are severe stunting of the potato plants and the production of small tubers. There are two kinds, white and yellow, the latter more in the south.
The problem builds up year after year and eventually no crop is obtained. The cysts remain in the soil, infecting new potato plants as soon as they begin to grow. The only remedy is to cease growing potatoes for at least five years, or grow resistant varieties. ‘Sante' and ‘Valor' are notably eelworm resistant, carrying resistance to both kinds of eelworms.