Nematology

Root-knot nematodes (Meloidogyne spp.) are sedentary endoparasites that penetrate plant roots as second-stage juveniles (J2) and induce gall formation (root knots) by triggering giant cells in the vascular tissue. They have the widest host range of any plant parasitic nematode — over 2,000 host species. Major species: M. incognita (most common in India), M. javanica, M. arenaria, M. hapla. Heavily attacked crops: tomato, okra, brinjal, potato, banana, groundnut, and cucurbits. Symptom: wilting, stunting, and visible galls on roots.

Root-knot nematodes (Meloidogyne) induce galls on roots; the female remains soft-bodied and embedded in root tissue. Cyst nematodes (Heterodera and Globodera) form a hardened cyst — the dead, tanned body of the female — which protects eggs for decades in soil. Heterodera avenae attacks wheat and barley; H. cajani attacks pigeonpea; Globodera rostochiensis (golden cyst nematode) attacks potato. Cysts can remain viable in soil for 20+ years, making them harder to eradicate than root-knot nematodes.

Carbofuran (Furadan 3G) is a carbamate nematicidal granule applied to soil at planting — typically at 1 kg ai/ha in furrows or around planting holes. It controls root-knot, cyst, and reniform nematodes by inhibiting acetylcholinesterase. Neem cake (250 kg/ha) is the standard organic alternative — it releases nematicidal compounds (azadirachtin) on decomposition and improves soil biology. Paecilomyces lilacinus is the most widely used fungal biocontrol agent against root-knot nematodes.

Radopholus similis (burrowing nematode) is a migratory ectoparasite / endoparasite that moves through root cortex tissue, causing 'blackhead disease' or 'spreading decline' in banana and citrus. In banana, it causes toppling disease — roots are so destroyed the plant cannot support the weight of a bunch. It is one of the world's most economically damaging nematodes and is a quarantine pest in many countries. Management: hot water treatment of planting material (55°C for 20 minutes) for banana suckers.

Five main strategies: (1) Chemical — carbofuran 3G at 1 kg ai/ha, phorate for soil application; (2) Biological — Paecilomyces lilacinus (fungal), Pochonia chlamydosporia (egg parasitoid), Bacillus firmus; (3) Organic — neem cake 250 kg/ha, FYM enriched with bioagents; (4) Cultural — crop rotation with non-hosts (maize, sorghum), deep summer ploughing to expose cysts, resistant varieties; (5) Physical — soil solarisation using transparent PE film (40–45 days in summer kills nematodes in top 15 cm).

Damage thresholds vary by nematode and crop: Meloidogyne incognita on tomato — 1 egg mass/200g soil; M. incognita on okra — 2 juveniles/g soil; Heterodera avenae on wheat — 5 cysts/250g soil; Rotylenchulus reniformis on cotton — 1,000 juveniles/250g soil. Economic Threshold Level (ETL) concept from IPM is applied to nematodes similarly to insect pests — treatment is warranted only when population exceeds ETL to justify chemical cost.