Management of nematodes may be approached by using a combination of methods in an integrated pest management system or may involve only one of these methods. Some of the most commonly practiced methods include physical control, cultural management, crop rotation, use of trap crops, use of resistant and tolerant cultivars and chemicals.
Method # 1. Physical Control:
Nematodes in soil may be killed by soil solarisation. Soil is covered with one or two layers of polyethylene film and sun light is used for raising soil temperature. This is very effective for top soil in hot tropical summer months. Eggs and juveniles of nematodes get killed by exposure for 1-24 h at 41-47°C and repeated exposure to lethal temperature for sub lethal period has been observed to have cumulative lethal effect.
Cultural management methods have the advantage of offering low cost options for nematode management without toxicity or residue problems. Cultural practices includes sanitation of field, deep summer ploughing, fallowing, crop rotation with non-host crops, application of organic manures etc.
Age old practice of burning crop residues that lies on field surface should be promoted. It is suggested that root systems of susceptible crop should be removed and destroyed immediately after harvest. Keeping fields weed free is advocated to keep the nematode populations in general under check.
b. Fallowing and Deep Summer Ploughing:
Fallowing is a common practice of keeping the soil free from all vegetations for specific period by occasional ploughing during hot and dry weather. Complete fallow without any plant or weed to grow is the best method. This method invariably ensures that parasitic nematodes will have no host to feed and thereby will not be reproduced.
Hot summer months in India can be utilised profitably for summer ploughing as it is known to be a very effective farm operation in reducing nematode population by exposing the egg and juvenile stages to high temperature.
Control of plant parasitic nematodes by crop rotation is based on the fact that some species of nematodes are able to feed and multiply on certain crop plants but not on others. Hosts on which they cannot feed but can abundantly reproduce but can are referred to as non-host.
The crops to be grown in between the susceptible host crops should be either resistant or immune to nematodes. Rotation with graminaceous poor hosts such as wheat, barley, ragi, maize, sorghum, etc. or dicot like mustard, sesame, asparagus and so on has some antagonistic effects to suppress root-knot nematodes. Haque and Gaur (1985) reported that the incorporation of mustard, sesame, maize, wheat etc. suppressed nematode population in India.
Tomato cv. SL 120, castor cv. A 39-1 and cotton cv. Hy-6 cultivated in Kharif-Rabi followed by summer green gram in summer effectively checked root-knot nematode (13- 17%) and enhanced grain yield of summer green gram cv. Gujarat 2 by 53-76%. In general, the inclusion of Marigold (Tagetes patula), Zinnia (Zinnia elegans), Sugarcane (Saccharum officinalis), Maize (Zea mays) and chilli in cropping sequence reduces reniform nematode population.
Incorporation of organic substances includes organic manures, green manures and soil amendments like oil cakes (neem and castor cake) reduce the population of nematodes. Mojumder and Mishra (1991) reported the nematicidal effects of water soluble portion of oil seed cakes of neem, mustard, karanj and groundnut against M. incognita.
Several species of Crotalaria (C. spectabilis) and Castor (Ricinus communis L.) reported to trap M. incognita and M. javanica and thereby deplete the nematode population. Antagonistic plants such as Marigold (Tagetes erecta and T. patula) and Chrysanthemum proved to be effectively reduces Meloidogyne population. Sannhemp (Crotolaria spectabilis) which traps root-knot larvae can be grown and used as a green manure.
Replacing the susceptible varieties with genetically resistant ones is a convenient option for nematode management. In India, earlier several attempts have been made to screen the available indigenous and exotic crop germplasm to locate resistance sources by many researchers but still work is restricted to evaluation of germplasm against root-knot and reniform nematodes.
Khana and Nirula (1964) reported a potato selection HC 294 resistant to M. ingonita. Similarly, a tomato selection Pusa 120 exhibited resistance to this nematode. Patel et al., (1990) evaluated different tomato cultivars like NT 3, NT 8, NT 12 and SL 120 and proved that cultivar NT 8 and SL 120 were highly resistant whereas NT 3 and NT 12 were resistant to M. incognita. The resistant lines need to be utilised in breeding programme.
Soil incorporation with predatory fungus, Paecilomyces lilacinus reduced the nematode population by egg parasitisation of some nematodes including M. Incognita. Seed treatment (@ 5g-1 /kg seed) as well as soil application (@ 2.5 kg-1/ha) with Pseudomonas fluorescens or Trichoderma viride is effective against most of the nematodes. Soil application with Pseudomonas fluorescens @ 10g-2/m reduced the nematode population in vegetable nurseries.
Nematicides are generally not recommended, particularly in vegetable crops, in view of their high cost and residue problem in fruit. However, intensive cultivation of high-value crops make their use unavoidable.
Following nematicides are recommended for judicious use:
a. Treatment of nursery beds along with carbofuran @ 3kg a.i.-1/ ha (0.3g a.i.-1/ m2) in case of transplanted crops at sowing.
b. Seed dressing of bold seeded crops like okra, cucurbits, cowpea etc. with carbosulfan 25 EC @ 2-3% w/w.
c. Before transplanting of seedlings dipping of root in Thiaonazin 500 ppm for 15 min or carbosulfan 1000 ppm solution for 1 hr.
d. Before sowing or pre-plant soil application of carbofuran @ 1-2 kg a.i.-1/ ha in field crops and @ 50-100g-1/ tree in horticultural crops.