University of Maryland Extension

Root-Knot Nematodes - Vegetables

roots covered with nodules

Back to Common Problems - Vegetables

Publication: (PDF) HG 72 Root Knot Nematodes

Swelllings or nodules on plant roots can indicate root knot nematodes. The most common root infecting nematodes of vegetable crops are two root knot nematode species- Meloidogyne hapla and Meloidogyne incognita. Root knot nematodes are very small (0.5 to 0.75 mm), colorless roundworms that dwell in the soil, enter plants roots as tiny larvae, and cause swellings (root knots) that can be easily seen (distinguishable from the nitrogen-fixing nodules found on legumes because the latter can be easily rubbed off the roots whereas root-knots are firmly attached). The root system may be reduced in size and prone to injury from soil pathogens. Plants fail to establish, are stunted, wilt in hot weather and decline. Affected plants produce fewer and smaller fruit. Root crops such as carrots may be deformed (forked carrots) or have hairy roots with nodules. Symptoms spread through a site as the season progresses and succeeding generations of juveniles hatch out.

forked rootssweet potato
Stunting and forking of carrots from root knot nematode.Nematode damage to sweet potato.

Most vegetable crops may serve as host plants. Both species thrive in a wide variety of soil types but are more commonly found on light textured soils (those with a high percentage of sand.) Soil and tissue testing is the only accurate method to determine that nematodes are the cause of plant injury. Microscopic examination is required to identify these tiny worms. Some nematodes also serve as vectors for plant virus diseases such as tomato ring spot and tobacco ringspot.

Biology of Root-knot Nematodes: The root knot nematode takes about 27 days to grow from egg to adult under normal growing season temperatures. The immature root knot nematode molts once in the egg, emerges as the infective larval stage and enters plant roots. The female nematode remains inside the root for the rest of her life, causing the swelling or "root knot" to be formed around her body, which swells into a spherical shape. At maturity, the female extrudes her eggs into a tan gelatinous mass that can be seen on the root knot surface. Each female can produce one egg mass containing from 300 to 500 eggs.

tomato with root-knot nematode damage
Plants fail to establish, are stunted, wilt in hot weather and decline.

Management:  Prevention and biological control are the keys to success in managing this pest. There are no chemical treatments available to home gardeners. Plant only resistant varieties of susceptible plants. Resistant tomato cultivars will have an "N" after the cultivar name (usually VFN for tomato). Keep weeds down and rotate susceptible crops or avoid planting them for a few years. Pull up and remove badly infested plants. Some "green manure" crops (cover crops), such as mustard and rape, produce compounds that suppress root-knot nematodes. Enhancing the biological activity of the soil, through incorporation of compost, can also help suppress root-knot nematode populations.

Dig up suspect plants, wash soil off the roots and carefully inspect for swellings. If root-knot is strongly suspected have your soil tested and follow recommendations.

Maintained by the IET Department of the College of Agriculture and Natural Resources. © 2017. Web Accessibility