The swellings on the roots of vegetable plants are caused by the root-knot nematode, Meloidogyne hapla or M. incognita. This tiny nematode (microscopic worm), or eelworm, causes root swellings on many vegetable and ornamental crops. Carrot roots and potato tubers may be lumpy, while fibrous-rooted plants will have swellings up to 1/4 inch in diameter.

Gently remove infected plants with galls from the garden and bury or burn them. Rotate with non-susceptible garden crops such as sweet corn. Plant nematode-resistant varieties such as VFN tomato types (the N signifies resistance to nematodes). If parts of the garden are contaminated with this nematode, move the garden and replant the contaminated areas with tall fescue grass for two or three years before going back in with vegetables. Crop rotation using some marigold (Tagetes) species is known to give good control of nematodes, especially Pratylenchus spp. and Meloidogyne spp.