Managing Plant-Parasitic Nematodes in Vegetable Production

Plant-parasitic nematodes, particularly root-knot nematodes (Meloidogyne spp.) and root-lesion nematodes (Pratylenchus spp.), cause significant yield losses in vegetable production across Southern Africa. Losses of 20–30% are common, and severe infestations can make commercial vegetable production non-viable.

Root-Knot Nematodes (Meloidogyne spp.)

The most important nematode pests in vegetable production. The four main species (M. incognita, M. javanica, M. arenaria, M. hapla) affect virtually all vegetable crops.

Symptoms:

• •Galls (knots) on roots of varying sizes
• •Stunted, chlorotic plants
• •Plants wilt readily in dry weather
• •Symptoms appear in patches in the field

Crops most affected: Tomato, pepper, carrot, potato, beans, cucurbits

Root-Lesion Nematodes (Pratylenchus spp.)

Symptoms:

• •Brown lesions and necrosis on roots
• •No galls
• •Stunted growth and yellowing
• •Patches of poor crop growth

Chemical Control (Nematicides)

Application Methods

Preplant soil incorporation: Apply nematicides 1–2 weeks before planting and incorporate to 20–30 cm depth. Allow off-gassing before planting.

In-furrow at planting: Apply nematicide granules or liquids directly into the planting furrow at seeding or transplanting.

Drip irrigation (chemigation): Apply systemic nematicides through drip tape for in-season suppression.

Cultural Practices

• •Rotation: Rotate with non-host or poor-host crops (cereals, onions)
• •Resistant cultivars: Use Meloidogyne-resistant tomato rootstocks or cultivars (Mi gene)
• •Solarisation: Cover moistened soil with clear polythene for 4–6 weeks in summer
• •Green manures: Incorporate Tagetes (marigold) or crotalaria into the soil
• •Sanitation: Clean equipment thoroughly; avoid moving contaminated soil

Scouting

Take soil samples before planting (top 30 cm) for nematode extraction and identification. Repeat-sample mid-season from the root zone. Action thresholds vary by crop and species.