Root-Knot Nematode

Diagnosis relies mainly on digging up roots and looking for characteristic galls or swellings, which can range from small bumps to large, knotted masses depending on the species and level of infestation.

Root gall

A swelling on the root caused by the plant’s reaction to a feeding nematode.

Nodule vs. gall

On legumes such as common bean, nitrogen-fixing rhizobial nodules are typically smaller, more uniform, and detach easily, unlike firmly attached nematode galls.

Juvenile

The motile, infective larval stage that seeks out and penetrates root tips.

Eggs hatch in soil into motile juveniles that seek out and penetrate root tips. Once inside, juveniles become sedentary, establishing a specialized feeding site and inducing gall formation as they develop through several moults to maturity.

Mature females, often pear-shaped, can produce large numbers of eggs in a gelatinous mass on or near the root surface. Generation time is strongly temperature-dependent, with multiple generations possible per season in warm climates.

Galled roots have a reduced capacity to take up water and nutrients, leading to stunting, yellowing, and wilting under moisture stress, along with yield loss. Secondary infection by soil-borne fungi or bacteria through damaged root tissue can compound losses.

The host range is unusually broad, including tomato, carrot, cucumber, and common bean among many other vegetables and field crops.

Soil sampling and laboratory assay for nematode presence and population levels before planting a susceptible crop, combined with digging and inspecting roots of symptomatic plants for galls, are the main monitoring approaches. Field history is also informative, since populations build up under repeated susceptible cropping.

Root-knot nematode management focuses on reducing soil populations and protecting roots rather than direct treatment of established infestations.

• Use resistant or tolerant varieties and rootstocks where available
• Rotate with non-host or poor-host crops to reduce soil population over time
• Maintain soil organic matter and biological activity, which can support naturally suppressive organisms
• Avoid moving infested soil or equipment between fields where practical
• Base planting decisions on pre-plant soil sampling where available