The following points highlight the six main types of management of nematodes pests. The types are: 1. Cultural Management 2. Biological Management 3. Regulatory Management 4. Regulatory Management 5. Integrated Management of Nematodes.
Nematode Pest: Type # 1. Cultural Management:
The affectivity of cultural method depends upon the proper knowledge of life history, population dynamics host range of the plant parasitic nematodes infesting crops. The cultural practices include crop rotation, fallowing, flooding, sanitation, ploughing during summer season, mulching, organic manure, spacing of plants in the field, time of sowing, resistant varieties etc.
Nematode management through inter cropping and crop rotation is based on the fact that some species of nematodes are able to feed and multiply only on host crop. Rotation is a very old practice for reducing soil borne problems. Rotation to non-host crops may cause many of those pests to cease reproduction and allow natural mortality factors to reduce their numbers.
Flooding or fallowing may be used to help reduce numbers of nematode pests. The period of flooding appears to vary with several factors such as kind of soil, season etc. Warm conditions are said to reduce the period of time required for control. Juveniles (larvae) are more easily killed by flooding than eggs.
The period of flooding needs to be worked out for each condition. Fallow periods in cropping sequences can also reduce nematode populations. The summer ploughing 2-3 times during hottest period of the year help to expose nematodes to the drying action of sun and wind and reduce the population.
Haque and Prasad (1982) reported drastic reduction of plant parasitic nematodes and significantly increased the yield with three deep ploughing. The intensity of symptoms was directly related to the inoculum levels.
Sanitation terms covers a wide range of cultural practices, including weed control, crop residue destruction and disinfestations of farm equipment before moving it from heavily infested fields to uninfected fields.
In monocultures, eliminating the weed hosts can be important in reducing the populations of plant parasitic nematodes. Soil temperature plays crucial role in the activities of plant parasitic nematodes, the time during which crop is planted is important.
The addition of inorganic fertilizers alone without organic manure usually increases the nematode population and disease intensity. NH4-N reduces the disease incidence while NO3-N may increase the same.
Particular forms as well as dose and proportion of NPK may also reduce or increase the incidence of disease. Use of tolerant/ resistant varieties is most practical approach for the management of nematode diseases.
Crop cultivars resistant to phytonematodes can be the most useful and cheapest means of nematode control for the small-scale farmers. Nematicidal plants with roots containing nematicidal substances have been investigated.
These toxic substances reduce the population level of some nematode species. African marigolds (Tagetes spp.), asparagus, crotalaria, mustard and several cruciferous plants have been reported to produce toxic substances.
Soil amendments with green manure, compost, oil cakes of neem, mahua, mustard, groundnut, cotton, linseed, karanj and saw dust etc. have been found to reduce nematode populations. Neem, karanj and groundnut cakes incorporated into soil at the rate of 1,500 kg/ha give good control of plant parasitic nematodes and could be practiced wherever possible.
Apart from encouraging the multiplication of natural enemies like nematode trapping fungi, the decomposition products of these organic amendments are toxic to nematodes. Use of organic manures is of great value since the decomposition products and promotion of natural enemies decrease nematode populations.
The amount of oil cakes or any organic matter to be incorporated depends on various factors like, soil type and texture, crop to be planted, the predominant nematode fauna of the soil and the amount of soil moisture present in the soil.
In trap crops when grown in infested soils, the nematodes penetrate into the root system and start multiplying. Before the nematodes complete its life cycle the plants are uprooted and destroyed.
Applications of botanicals are easy, environmentally safe, and having no phytotoxic effect on crops. The inhibition of root-knot development may be due to the accumulation of toxic by products of decomposition to increased phenolic contents resulting in host resistance, or to changed physical and chemical properties of soil inimical to the nematodes.
One of the most economical and effective ways to control plant parasitic nematodes is the growing of nematode resistant plant cultivars. The identification of a dominant Mi gene importing resistance to the root- knot nematodes and its linkage to an acid phosphates gene is a major break through in this area of research.
Nematode Pest: Type # 2. Biological Management:
Use of biocontrol agents in nematode management of vegetables are increasing. Application of natural enemies of plant parasitic nematodes for controlling nematode population is an essential component of eco-friendly management.
Nematologists in all over the world are working very hard to identify and lean to manipulate natural enemies of nematodes so they can be used as biological control agents. Nematodes have many natural enemies including fungi, bacteria and predacious nematodes.
Certain fungi capture and kill nematodes in the soil. Arthrobotrys spp., Dactylaria spp., Dactylella spp., Catenaria spp., and Trichothecium spp., are the genera most commonly represented. The biological control of root knot nematode on tomato under green-house condition by using predaceous fungi has been reported Singh 2001; Bandyopadhya 2001.
Some fungi capture nematode by adhesion, but many employ specialized devices that include networks of adhesive branches, stalked adhesive knobs, non-constricting rings and constricting rings. The surface of the nematode is penetrated and the fungus hyphae grow throughout the nematode body, digesting and absorbing its contents.
Under favorable conditions, large numbers of nematodes may be captured, and killed especially by those fungi that form adhesive net-works or hyphal loops. Trichoderma harzianum, Trichoderma virens, Aspergillus niger, Paecilomyces lilacinus, Pochonia chlamydosporia are found promising biocontrol agents.
Davide and Zorilla (1985) while investigating the biocontrol potential of P. lilacinus against M.incognita on okra found the fungus to be quite effective and economically better than nematicides. According to Shahzad and Ghaffar (1984) carbofuran at the rate 1 kg a.i/ha was less effective than P. lilacinus against M. incognita.
Now mycorrhiza is not restricted to its use only as biofertilizers, its potential role in the biological control of plant parasitic nematodes is reported by many workers. Sikora (1979) found that prior presence of VAM fungi Glomus mosseae has resulted into an increase in plant resistance against Meloidogyne spp.
A bacterial parasite of nematodes Pasteuria penetrans, has received much attention and research effort in recent years, P. penetrans is probably the most specific obligate parasite of nematodes, with a life cycle remarkably well adapted to parasitism of certain phytonematodes.
It directly parasitizes juvenile nematode, thus affects penetration and reproduction. Pasteuria penetrans can survive several years in air dried soil apparently without loss of viability.
Seed bacterization, soil drenching and bare root dip application with Pseudomonas fluorescens, Pasteuria penetrans, Bacillus subtilis, B. polymyxa effectively controls plant parasitic nematodes was also reported by many workers. Among the predatory nematodes, monarchs may be proved efficient predators because of stronger predatory potential, high rate of predacity and high strike rate.
Nematode Pest: Type # 3. Chemical Management:
Many of the nematicides are broad spectrum volatile soil fumigants that are active against not only nematodes but also insects, fungi and bacteria living in the soil. Two major groups of nematicides are distinguished by the manner in which they spread through the soil. Soil fumigants are gases in cylinders or liquids which spread as gases from the point where they are infected into the soil.
Non fumigant nematicides include a variety of water soluble compounds which are applied to the soil as liquid or granular formulations. Most belong to the carbamate or organophosphate families of pesticides. These distributions in the soil depend on physical mixing during application and moving in solution in soil water.
There are no perfect nematicides for all purposes. Nematicides vary in their effectiveness against different kinds of nematodes, ease to handling, cost effect on other classes of pests (weeds, disease organisms, and insects) behavior in different soils, toxicity to different plants and availability.
The performance of the nematicides will depend on soil conditions, temperatures and rainfall. A yield benefit is not guaranteed and nematicides are expensive. The older nematicides are mostly fumigants which are applied in soil. These are seldom recommended because of their hazardous nature and high toxicity to non-target organisms.
Recently, large number of non-fumigant and systehiic nematicides are available which are safe on plant. DBCP (nemagon) has been found very effective for standing crops against root-knot nematodes but its use has been suspended due to adverse effect on human beings.
Carbofuran 3G (furadon), phorate 10G (thimet), fenamiphos (nemacur), fensulphothion (dasanit) have been recommended for a variety of vegetable crops by several workers.
The development of the H. cajani nematode was also delayed in pot condition experiment which was treated with carbofuran, phorate and aldicarb nematicides. The dose and method of application would vary with crop.
Chemicals and Phytoalexins that have implications in the nematode control, synthetic pheromones to disrupt nematode reproduction and chemicals that directly interfere with nematode chemoreceptors should be exploited for nematode population management.
Prasad (1990) studied the control by seed pelleted with carbofuran, aldicarb, sulfone at the rate 3 and 6% w/w. Application of carbosulfan nematicides reduced root-knot nematodes in vegetables and seed treatment was more effective than soil application.
Nematode Pest: Type # 4. Regulatory Management:
Numerous attempts have been made to prevent the introduction of nematodes into countries or provinces by means of quarantine. Quarantines are established by legislative action in parliament, etc., and usually give quarantine authorities power to make and enforce regulations to accomplish the purpose.
Such regulations usually prohibit bringing infected seeds into protected areas where similar crops might become infected.
Nematode Pest: Type # 5. Physical Management:
The scientific principle involved in thermotherapy is that the pathogens present in soil and plant materials are inactivated or eliminated at temperatures non-lethal for the host tissues.
Physical means of nematode control includes heat treatment of soil, solar drying, steam sterilization, hot water treatment and soil solarization. Soil solarization with transparent polyethylene sheet has been attended as a means of raising the soil temperature to lethal levels to control soil pathogens.
Soil solarization, a method of pasteurization can effectively suppress most species of nematode along with other microbes and weeds under field conditions. Generally, sheets of 50-100 pm thickness are most suitable for raising the soil temperature.
The use of transparent polyethylene had yielded better results than black sheets, since transparent sheet transmit most of the incident radiation to soil. Additions of salt, sugar, charcoal etc. create osmotic stress on nematodes and can be used for controlling nematodes.
Nematode Pest: Type # 6. Integrated Management of Nematodes:
Integrated nematode management is based upon the system approach, follows location specific principle and is environment specific.
Utilization of the best combination of available management strategies for the pest complex at hand (nematodes, insect pests, disease organisms, weeds etc.) constitutes an integrated crop protection system. Resistant-cultivars, crop rotation, pesticides, and sanitary and cultural practices can all be employed to the best possible advantage.
An integrated management strategy prevents the excessive build up any single nematode, insect, or disease population and minimizes the development of pest resistance to any single tactic. Integrated pest management systems require flexibility and depend upon the specific pest problem and locally available management options.
A fixed set of recommendations may keep a pest complex in check for a limited period of time, but as the pest population shifts, recommendations will have to change also.
Therefore, system development takes into account many factors including the species and race of pests present, the availability of resistant host plants, the longevity of the pest, and the crops, cropping systems, and climate of the geographical region. The end result is a management strategy tailored to fit the unique circumstances of each pest situation.