Root Knot Nematodes on Vegetables

Severe root-knot nematode symptoms on Swiss chard roots

Updated: February 20, 2023

Appearance

Root-knot nematodes are very small (0.5 to 0.75 mm), colorless roundworms.
The most common root infecting nematodes of vegetable crops are two root-knot nematode species, Meloidogyne hapla and Meloidogyne incognita.

They 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).
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).
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.
Some nematodes also serve as vectors for plant virus diseases such as tomato ring spot and tobacco ringspot.

Swellings or nodules on plant roots can indicate root-knot nematodes.
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.

On left stunted and forked carrots.
Photo: S.A. Johnson, Rutgers
Yellowing of plants in patches in a field infested with root-knot nematode.
Edward Sikora, Auburn University, Bugwood.org

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.

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 the 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.