Nematodes has the potential of creating wholesale destruction of crops, especially those grown in regions of wide weather fluctuation. In fact, these plant pests sometimes limit the kinds & varieties of crops that can be grown. The damage they cause may sometimes by mistaken for that caused by unfavorable weather. Epidemics may destroy crops completely. The body of the nematode is elongate without any segment. It is cylindrical tapering at both the ends especially towards the tail. The females may swell to become spherical. The size of plant nematode ranges from 0.2mm to 10mm & commonly 0.5 to 1.5 mm range.
Plant Parasitic nematodes –
The important Parasitic nematodes are –
- Ufra disease of rice – Ditylenchus angustus
- Potato tuber rot nematode – Ditylenchus destructor
- Wheat ear cockle – Auguina tritici
- Potato cyst nematode – Globodera rostochinensis.
- Root knot nematode of cucumber & tomato – Meloidogyne incognita
- Root knot nematode of tobacco, sugarcane, banana & vegetables – Meloidogyne javanka.
- ‘Molya disease’ of wheat & barley – Heterodera avenae.
- Rice white tip nematode – Aphelenchoides besseyi
- Citrus nematode causing slow decline of citrus – Tylenchulus semipenetrans
- Banana rhizome rot, pepper slow wilt – Radopholus similis
- Reniform nematode in cotton, maize, cowpea & black gram & banana – Rotylenchus reniformis.
- Root lesion of coffee – Pretylenchus coffeae
- virus transmitting nematodes –
1. Longidorus macrosoma – transmits prunus necrotic ring spot virus
2. Xiphinema americanum – transmits tabacco ring spot virus.
3. Paratrichadorus teres – transmits pea early browning virus.
4. Trichodorus similis – transmits tobacco rattle virus.
Management of nematode diseases –
- Crop rotation – The susceptible crops should be rotated with non-susceptible crops to eliminate or reduce nematode population. Heterodera, Globodera & Meloidogyne does not survive in soil for long time & hence they can be controlled by proper crop rotation.
- Clean Seed – Angunia tritici galls are found mixed with wheat seed. Seeds should be cleaned & the galls should be eliminated.
- Cleaning of farm implements – Nematodes do not move more than a few inches a year of their own accord & most spread is passive. The infested soil sticking on the farm implements should be cleaned before taking them to new field.
- Selection of healthy propagating material – Banana rhizome rot nematode spreads through suckers. Hence healthy suckers alone should be used.
- Organic Manures – Organic manures enhance nematophagous fungi & antogonistic bacteria & hence reduce the nematode infection.
- Enemy plants – Root exudates of some plants are inhibitory to nematodes. They are called enemy plants. Tagets erecta reduces pratylenchus infection. Asparagus reduces Paratrichodorus, christiei crotoloria reduces Meloidogyne population. White mustard reduces potato cyst nematode. The enemy plants can be grown as an alternate crop or as an intercrop. Intercropping will be more beneficial.
- Trap cropping – Oats is an efficient trap crop for Heterodern avenae which attacks wheat & barley. Oats is ploughed in before the nematodes mature.
- Biological control – Many nematophagous fungi have been reported. Pseudomonas is antagonistic to the nematodes. Virus infection in Meloidogyne incognita has been reported. Amoeboid organisms attack larvae of potato cyst nematode. Huge amount of organic matter is essential to activate these biological agents for control of nematode diseases.
- Physical methods – The infested soil can be sterilized with steam. Potato cyst nematodes are killed by passing the steam into the soil thro’ perforated pipes in western countries. Hot water treatment will be useful to control cyst nematodes in potato tubers. Rice white tip nematode can be eliminated by hot water treatment.
- Chemical control – Many fumigants are available to control nematodes. Methyl bromide (Dowfume MC-2) at 400-900 kg/ha, dichloropropene (Telone) at 500-900 kg/ha, dibromochloro propane, (Nemagon) at 120 kg/ha & metham – sodium (vapam) are useful. Some of the granules also reduce nematode population. Aldicarb (Temik) at 11kg/ha & Oxamyl (vydate) at 11kg/ha. effectively control nematode. Carbofuran 075-1.0 kg/ha also reduces nematodes.
- Resistant varieties have been developed against many nematodes.
- Quarantine – Potato cyst nematode is a quarantine objective & strict quarantine prevents the movement of the nematode from one country to another.